Around 1.8 Billion B.C.T., the Columbia supercontinent was formed.
Columbia, also known as Nuna and Hudsonland, was one of Earth's ancient supercontinents. It is thought to have existed approximately 1.8 to 1.5 billion years ago (1.8-1.5 Ga) in the Paleoproterozoic Era. The assembly of the supercontinent Columbia (Nuna) was completed by global-scale collisional events during 2.1–1.8 Billion B.C.T. It consisted of the proto-cratons that made up the former continents of Laurentia, Baltica, Ukrainian Shield, Amazonian Shield, Australia, and possibly Siberia, North China, and Kalaharia as well. The evidence of Columbia's existence is based upon geological and paleomagnetic data.
Columbia is estimated to have been about 12,900 kilometers (about 8,000 miles) from North to South, and about 4,800 kilometers (about 3,000 miles) across at its broadest part. The east coast of India was attached to western North America, with southern Australia against western Canada. Most of South America spun so that the western edge of modern-day Brazil lined up with eastern North America, forming a continental margin that extended into the southern edge of Scandinavia.
Columbia was assembled along global-scale 2.0 to 1.8 Ga collisional orogens and contained almost all of Earth’s continental blocks. The cratonic blocks in South America and West Africa were welded by the 2.1-2.0 Ga Transamazonian and Eburnean Orogens; the Kaapvaal and Zimbabwe cratons in southern Africa were collided along the 2.0 Ga Limpopo Belt; the cratonic blocks of Laurentia were sutured along the 1.9–1.8 Ga Trans-Hudson, Penokean, Taltson–Thelon, Wopmay, Ungava, Torngat, and Nagssugtoqidain Orogens; the Kola, Karelia, Volgo-Uralia, and Sarmatia cratons in Baltica (Eastern Europe) were joined by the 1.9–1.8 Ga Kola–Karelia, Svecofennian, Volhyn-Central Russian, and Pachelma Orogens; the Anabar and Aldan Cratons in Siberia were connected by the 1.9–1.8 Ga Akitkan and Central Aldan Orogens; the East Antarctica and an unknown continental block were joined by the Transantarctic Mountains Orogen; the South and North Indian Blocks were amalgamated along the Central Indian Tectonic Zone; and the Eastern and Western Blocks of the North China Craton were welded together by the 1.85 Ga Trans-North China Orogen.
Following its final assembly at 1.8 Ga, the supercontinent Columbia underwent long-lived (1.8–1.3 Ga), subduction-related growth via accretion at key continental margins, forming a 1.8-1.3 Ga great magmatic accretionary belt along the present-day southern margin of North America, Greenland, and Baltica. It includes the 1.8-1.7 Ga Yavapai, Central Plains and Makkovikian Belts, 1.7-1.6 Ga Mazatzal and Labradorian Belts, 1.5-1.3 Ga St. Francois and Spavinaw Belts, and 1.3-1.2 Ga Elzevirian Belt in North America; the 1.8-1.7 Ga Ketilidian Belt in Greenland; and the 1.8-1.7 Transscandinavian Igneous Belt, 1.7-1.6 Ga Kongsberggian-Gothian Belt, and 1.5-1.3 Ga Southwest Sweden Granitoid Belt in Baltica. Other cratonic blocks also underwent marginal outgrowth at about the same time. In South America, a 1.8-1.3 Ga accretionary zone occurs along the western margin of the Amazonia Craton, represented by the Rio Negro, Juruena, and Rondonian Belts. In Australia, 1.8-1.5 Ga accretionary magmatic belts, including the Arunta, Mount Isa, Georgetown, Coen, and Broken Hill Belts, occur surrounding the southern and eastern margins of the North Australia Craton and the eastern margin of the Gawler Craton. In China, a 1.8-1.4 Ga accretionary magmatic zone, called the Xiong’er belt (Group), extends along the southern margin of the North China Craton.
Columbia began to fragment about 1.6 billion years ago, associated with continental rifting along the western margin of Laurentia (Belt-Purcell Supergroup), eastern India (Mahanadi and the Godavari), southern margin of Baltica (Telemark Supergroup), southeastern margin of Siberia (Riphean aulacogens), northwestern margin of South Africa (Kalahari Copper Belt), and northern margin of the North China Block (Zhaertai-Bayan Obo Belt).
Thursday, November 29, 2012
Wednesday, November 28, 2012
2.1 Billion B.C.T. - Eukaryotes Arose
By 2.1 Billion B.C.T., eukaryotes (cells with nuclei) were present on this Earth.
A eukaryote is an organism whose cells contain complex structures enclosed within membranes. Eukaryotes may more formally be referred to as the taxon Eukarya or Eukaryota. The defining membrane-bound structure that sets eukaryotic cells apart from prokaryotic cells is the nucleus, or nuclear envelope, within which the genetic material is carried. The presence of a nucleus gives eukaryotes their name, which comes from the Greek eu ("good") and karyon ("nut" or "kernel"). Most eukaryotic cells also contain other membrane-bound organelles such as mitochondria, chloroplasts and the Golgi apparatus. All large complex organisms are eukaryotes, including animals, plants and fungi. The group also includes many unicellular organisms.
Cell division in eukaryotes is different from that in organisms without a nucleus (Prokaryote). It involves separating the duplicated chromosomes, through movements directed by microtubules. There are two types of division processes. In mitosis, one cell divides to produce two genetically identical cells. In meiosis, which is required in sexual reproduction, one diploid cell (a cell having two instances of each chromosome, one from each parent) undergoes recombination of each pair of parental chromosomes, and then two stages of cell division, resulting in four haploid cells (gametes). Each gamete has just one complement of chromosomes, each a unique mix of the corresponding pair of parental chromosomes.
Eukaryotes appear to be monophyletic, and thus make up one of the three domains of life. The two other domains, bacteria and archaea, are prokaryotes and have none of the above features. Eukaryotes represent a tiny minority of all living things; even in a human body there are 10 times more microbes than human cells. However, due to their much larger size their collective worldwide biomass is estimated at about equal to that of prokaryotes.
The origin of the eukaryotic cell is considered a milestone in the evolution of life, since they include all complex cells and almost all multicellular organisms. The timing of this series of events is hard to determine. Some acritarchs are known from at least 1.65 billion years ago, and the possible algae Grypania has been found as far back as 2.1 billion years ago.
Organized living structures have been found in black shales of the Palaeoproterozoic Francevillian B Formation in Gabon, dated at 2.1 billion years old. Eukaryotic life could have evolved at that time. Fossils that are clearly related to modern groups start appearing an estimated 1.2 billion years ago, in the form of a red algae, though recent work suggests the existence of fossilized filamentous algae in the Vindhya basin dating back perhaps to 1.6 to 1.7 billion years ago.
Biomarkers suggest that at least stem eukaryotes arose even earlier. The presence of steranes in Australian shales indicates that eukaryotes were present in these rocks dated at 2.7 billion years old.
A eukaryote is an organism whose cells contain complex structures enclosed within membranes. Eukaryotes may more formally be referred to as the taxon Eukarya or Eukaryota. The defining membrane-bound structure that sets eukaryotic cells apart from prokaryotic cells is the nucleus, or nuclear envelope, within which the genetic material is carried. The presence of a nucleus gives eukaryotes their name, which comes from the Greek eu ("good") and karyon ("nut" or "kernel"). Most eukaryotic cells also contain other membrane-bound organelles such as mitochondria, chloroplasts and the Golgi apparatus. All large complex organisms are eukaryotes, including animals, plants and fungi. The group also includes many unicellular organisms.
Cell division in eukaryotes is different from that in organisms without a nucleus (Prokaryote). It involves separating the duplicated chromosomes, through movements directed by microtubules. There are two types of division processes. In mitosis, one cell divides to produce two genetically identical cells. In meiosis, which is required in sexual reproduction, one diploid cell (a cell having two instances of each chromosome, one from each parent) undergoes recombination of each pair of parental chromosomes, and then two stages of cell division, resulting in four haploid cells (gametes). Each gamete has just one complement of chromosomes, each a unique mix of the corresponding pair of parental chromosomes.
Eukaryotes appear to be monophyletic, and thus make up one of the three domains of life. The two other domains, bacteria and archaea, are prokaryotes and have none of the above features. Eukaryotes represent a tiny minority of all living things; even in a human body there are 10 times more microbes than human cells. However, due to their much larger size their collective worldwide biomass is estimated at about equal to that of prokaryotes.
The origin of the eukaryotic cell is considered a milestone in the evolution of life, since they include all complex cells and almost all multicellular organisms. The timing of this series of events is hard to determine. Some acritarchs are known from at least 1.65 billion years ago, and the possible algae Grypania has been found as far back as 2.1 billion years ago.
Organized living structures have been found in black shales of the Palaeoproterozoic Francevillian B Formation in Gabon, dated at 2.1 billion years old. Eukaryotic life could have evolved at that time. Fossils that are clearly related to modern groups start appearing an estimated 1.2 billion years ago, in the form of a red algae, though recent work suggests the existence of fossilized filamentous algae in the Vindhya basin dating back perhaps to 1.6 to 1.7 billion years ago.
Biomarkers suggest that at least stem eukaryotes arose even earlier. The presence of steranes in Australian shales indicates that eukaryotes were present in these rocks dated at 2.7 billion years old.
Tuesday, November 27, 2012
2.4 Billion B.C.T. - The Great Oxygenation Event Begins
Around 2.4 Billion B.C.T., rising levels of oxygen in the atmosphere provided an environment in which eukaryotes (cells with nuclei) would come to flourish.
The Great Oxygenation Event (GOE), also called the Oxygen Catastrophe or the Oxygen Crisis or the Great Oxidation, was the biologically induced appearance of free oxygen (O2) in the Earth's atmosphere. Geological, isotopic, and chemical evidence suggest this major environmental change happened around 2.4 billion years ago.
Around 2.4 Billion B.C.T., cyanobacteria (see 3.5 Billion B.C.T. - Cyanobacteria Appeared) began producing oxygen by photosynthesis. Before the GOE, any free oxygen they produced was chemically captured by dissolved iron organic matter. The GOE was the point when these oxygen sinks became saturated and could not capture all of the oxygen that was produced by cyanobacterial photosynthesis. After the GOE the excess free oxygen started to accumulate in the atmosphere.
Free oxygen is toxic to anaerobic organisms and the rising concentrations may have wiped out most of the Earth's anaerobic inhabitants at the time. Cyanobacteria were therefore responsible for one of the most significant extinction events in Earth's history. Additionally the free oxygen reacted with the atmospheric methane, a greenhouse gas, triggering the Huronian glaciation, possibly the longest snowball Earth episode. Free oxygen has been an important constituent of the atmosphere ever since.
The Great Oxygenation Event (GOE), also called the Oxygen Catastrophe or the Oxygen Crisis or the Great Oxidation, was the biologically induced appearance of free oxygen (O2) in the Earth's atmosphere. Geological, isotopic, and chemical evidence suggest this major environmental change happened around 2.4 billion years ago.
Around 2.4 Billion B.C.T., cyanobacteria (see 3.5 Billion B.C.T. - Cyanobacteria Appeared) began producing oxygen by photosynthesis. Before the GOE, any free oxygen they produced was chemically captured by dissolved iron organic matter. The GOE was the point when these oxygen sinks became saturated and could not capture all of the oxygen that was produced by cyanobacterial photosynthesis. After the GOE the excess free oxygen started to accumulate in the atmosphere.
Free oxygen is toxic to anaerobic organisms and the rising concentrations may have wiped out most of the Earth's anaerobic inhabitants at the time. Cyanobacteria were therefore responsible for one of the most significant extinction events in Earth's history. Additionally the free oxygen reacted with the atmospheric methane, a greenhouse gas, triggering the Huronian glaciation, possibly the longest snowball Earth episode. Free oxygen has been an important constituent of the atmosphere ever since.
Wednesday, November 21, 2012
2.5 Billion B.C.T. - The Proterozoic Eon Begins
Around 2.5. Billion B.C.T., the Proterozoic Eon began.
The Proterozoic Eon is a geological eon representing the time just before the proliferation of complex life on Earth. The name Proterozoic comes from Greek and means "earlier life". The Proterozoic Eon extended from 2.5 billion years ago to 542 million years ago, and is the most recent part of the informally named "Precambrian" time. It is subdivided into three geologic eras (from oldest to youngest): the Paleoproterozoic, Mesoproterozoic, and Neoproterozoic.
The well-identified events of this eon were the transition to an oxygenated atmosphere during the Mesoproterozoic; several glaciations, including the hypothesized Snowball Earth during the Cryogenian period in the late Neoproterozoic; and the Ediacaran Period (635 to 542 million years ago) which is characterized by the evolution of abundant soft-bodied multicellular organisms.
One of the most important events of the Proterozoic Eon was the gathering up of oxygen (the Great Oxygenation Event) in the Earth's atmosphere. Though oxygen was undoubtedly released by photosynthesis well back in the time of the Archean Eon, it could not build up to any significant degree until chemical sinks — unoxidized sulfur and iron — had been filled. Up until roughly 2.3 billion years ago, oxygen was probably only 1% to 2% of its current level. Banded iron formations, which provide most of the world's iron ore, were also a prominent chemical sink; most accumulation ceased after 1.9 billion years ago, either due to an increase in oxygen or a more thorough mixing of the oceanic water column.
Red beds, which are colored by hematite, indicate an increase in atmospheric oxygen after 2 billion years ago. The oxygen buildup was probably due to two factors: a filling of the chemical sinks, and an increase in carbon burial, which sequestered organic compounds that would have otherwise been oxidized by the atmosphere.
Throughout the history of the Earth, there have been times when the continental mass came together to form a supercontinent, followed by the break-up of the supercontinent and new continents moving apart again. This repetition of tectonic events is called a Wilson cycle. It is at least clear that, about 1.0 billion years ago to 830 million years ago, most continental mass was united in the supercontinent Rodinia. Rodinia was not the first supercontinent; it formed at about 1.0 billion years ago by accretion and collision of fragments produced by breakup of the older supercontinent, called Nuna or Columbia, which was assembled by global-scale 2.0–1.8 B.C.T. collisional events. This means that plate tectonic processes similar to today's must have been active during the Proterozoic Eon.
After the break-up of Rodinia about 800 million years ago, it is possible the continents joined again around 550 million years ago. The hypothetical supercontinent is sometimes referred to as Pannotia or Vendia. The evidence for it is a phase of continental collision known as the Pan-African orogeny, which joined the continental masses of current-day Africa, South-America, Antarctica and Australia. It is extremely likely, however, that the aggregation of continental masses was not completed, since a continent called Laurentia (roughly equivalent to current-day North America) had already started breaking off around 610 million years ago. It is at least certain that by the end of the Proterozoic Eon, most of the continental mass lay united in a position around the south pole.
The fossil evidence for the first advanced single-celled organisms, eukaryotes and multi-cellular life, -- the Francevillian Group Fossils --, roughly coincides with the start of the accumulation of free oxygen. This may have been due to an increase in the oxidized nitrates that eukaryotes use, as opposed to cyanobacteria. It was also during the Proterozoic that the first symbiotic relationships between mitochondria (for nearly all eukaryotes) and chloroplasts (for plants and some protists only) and their hosts evolved.
The blossoming of eukaryotes such as acritarchs did not preclude the expansion of cyanobacteria; in fact, stromatolites reached their greatest abundance and diversity during the Proterozoic, peaking roughly 1.2 billion years ago.
Classically, the boundary between the Proterozoic and the Phanerozoic eons was set at the base of the Cambrian period when the first fossils of animals including trilobites and archeocyathids appeared. In the second half of the 20th century, a number of fossil forms have been found in Proterozoic rocks, but the upper boundary of the Proterozoic has remained fixed at the base of the Cambrian, which is currently placed at 542 million years ago.
The Proterozoic Eon is a geological eon representing the time just before the proliferation of complex life on Earth. The name Proterozoic comes from Greek and means "earlier life". The Proterozoic Eon extended from 2.5 billion years ago to 542 million years ago, and is the most recent part of the informally named "Precambrian" time. It is subdivided into three geologic eras (from oldest to youngest): the Paleoproterozoic, Mesoproterozoic, and Neoproterozoic.
The well-identified events of this eon were the transition to an oxygenated atmosphere during the Mesoproterozoic; several glaciations, including the hypothesized Snowball Earth during the Cryogenian period in the late Neoproterozoic; and the Ediacaran Period (635 to 542 million years ago) which is characterized by the evolution of abundant soft-bodied multicellular organisms.
One of the most important events of the Proterozoic Eon was the gathering up of oxygen (the Great Oxygenation Event) in the Earth's atmosphere. Though oxygen was undoubtedly released by photosynthesis well back in the time of the Archean Eon, it could not build up to any significant degree until chemical sinks — unoxidized sulfur and iron — had been filled. Up until roughly 2.3 billion years ago, oxygen was probably only 1% to 2% of its current level. Banded iron formations, which provide most of the world's iron ore, were also a prominent chemical sink; most accumulation ceased after 1.9 billion years ago, either due to an increase in oxygen or a more thorough mixing of the oceanic water column.
Red beds, which are colored by hematite, indicate an increase in atmospheric oxygen after 2 billion years ago. The oxygen buildup was probably due to two factors: a filling of the chemical sinks, and an increase in carbon burial, which sequestered organic compounds that would have otherwise been oxidized by the atmosphere.
Throughout the history of the Earth, there have been times when the continental mass came together to form a supercontinent, followed by the break-up of the supercontinent and new continents moving apart again. This repetition of tectonic events is called a Wilson cycle. It is at least clear that, about 1.0 billion years ago to 830 million years ago, most continental mass was united in the supercontinent Rodinia. Rodinia was not the first supercontinent; it formed at about 1.0 billion years ago by accretion and collision of fragments produced by breakup of the older supercontinent, called Nuna or Columbia, which was assembled by global-scale 2.0–1.8 B.C.T. collisional events. This means that plate tectonic processes similar to today's must have been active during the Proterozoic Eon.
After the break-up of Rodinia about 800 million years ago, it is possible the continents joined again around 550 million years ago. The hypothetical supercontinent is sometimes referred to as Pannotia or Vendia. The evidence for it is a phase of continental collision known as the Pan-African orogeny, which joined the continental masses of current-day Africa, South-America, Antarctica and Australia. It is extremely likely, however, that the aggregation of continental masses was not completed, since a continent called Laurentia (roughly equivalent to current-day North America) had already started breaking off around 610 million years ago. It is at least certain that by the end of the Proterozoic Eon, most of the continental mass lay united in a position around the south pole.
The fossil evidence for the first advanced single-celled organisms, eukaryotes and multi-cellular life, -- the Francevillian Group Fossils --, roughly coincides with the start of the accumulation of free oxygen. This may have been due to an increase in the oxidized nitrates that eukaryotes use, as opposed to cyanobacteria. It was also during the Proterozoic that the first symbiotic relationships between mitochondria (for nearly all eukaryotes) and chloroplasts (for plants and some protists only) and their hosts evolved.
The blossoming of eukaryotes such as acritarchs did not preclude the expansion of cyanobacteria; in fact, stromatolites reached their greatest abundance and diversity during the Proterozoic, peaking roughly 1.2 billion years ago.
Classically, the boundary between the Proterozoic and the Phanerozoic eons was set at the base of the Cambrian period when the first fossils of animals including trilobites and archeocyathids appeared. In the second half of the 20th century, a number of fossil forms have been found in Proterozoic rocks, but the upper boundary of the Proterozoic has remained fixed at the base of the Cambrian, which is currently placed at 542 million years ago.
Tuesday, November 20, 2012
3.5 Billion B.C.T. - Cyanobacteria Appeared
It is believed that cyanobacteria may have appeared on the Earth as early as 3.5 billion years ago.
Cyanobacteria, also known as blue-green bacteria, blue-green algae, and Cyanophyta, is a phylum of bacteria that obtain their energy through photosynthesis. The name "cyanobacteria" comes from the color of the bacteria (Greek: kyanós = blue).
The ability of cyanobacteria to perform oxygenic photosynthesis is thought to have converted the early reducing atmosphere into an oxidizing one, which dramatically changed the composition of life forms on Earth by stimulating biodiversity and leading to the near-extinction of oxygen-intolerant organisms. According to endosymbiotic theory, chloroplasts in plants and eukaryotic algae have evolved from cyanobacterial ancestors via endosymbiosis.
Stromatolites of fossilized oxygen-producing cyanobacteria have been found from 2.8 billion years ago, possibly as old as 3.5 billion years ago.
The biochemical capacity to use water as the source for electrons in photosynthesis evolved once, in a common ancestor of extant cyanobacteria. The geologic record indicates that this transforming event took place early in our planet's history, at least 2.45-2.32 billion years ago, and probably much earlier. Geo-biological interpretation of Archean Eon sedimentary rocks remains a challenge; available evidence indicates that life existed 3.5 billion years ago, but the question of when oxygenic photosynthesis evolved continues to engender debate and research.
A clear paleontological window on cyanobacterial evolution opened about 2.0 billion years ago, revealing an already diverse biota of blue-greens. Cyanobacteria remained principal primary producers throughout the Proterozoic (2.5 Billion B.C.T. - 543 Million B.C.T.), in part because the redox structure of the oceans favored photoautotrophs capable of nitrogen fixation.
The most common cyanobacterial structures in the fossil record are the mound-producing stromatolites and related oncolites. Indeed, these fossil colonies are so common that paleobiology, micropaleontology and paleobotany cite the Pre-Cambrian and Cambrian period as an "age of stromatolites" and an "age of algae."
Green algae joined the blue-greens as major primary producers on continental shelves near the end of the Proterozoic, but only with the Mesozoic era (251 Million B.C.T. - 65 Million B.C.T.) radiations of dinoflagellates, coccolithophorids, and diatoms did primary production in marine shelf waters take modern form.
Today, the blue-green bacteria remain critical to marine ecosystems as primary producers in oceanic gyres, as agents of biological nitrogen fixation, and—in modified form—as the plastids of marine algae.
Cyanobacteria, also known as blue-green bacteria, blue-green algae, and Cyanophyta, is a phylum of bacteria that obtain their energy through photosynthesis. The name "cyanobacteria" comes from the color of the bacteria (Greek: kyanós = blue).
The ability of cyanobacteria to perform oxygenic photosynthesis is thought to have converted the early reducing atmosphere into an oxidizing one, which dramatically changed the composition of life forms on Earth by stimulating biodiversity and leading to the near-extinction of oxygen-intolerant organisms. According to endosymbiotic theory, chloroplasts in plants and eukaryotic algae have evolved from cyanobacterial ancestors via endosymbiosis.
Stromatolites of fossilized oxygen-producing cyanobacteria have been found from 2.8 billion years ago, possibly as old as 3.5 billion years ago.
The biochemical capacity to use water as the source for electrons in photosynthesis evolved once, in a common ancestor of extant cyanobacteria. The geologic record indicates that this transforming event took place early in our planet's history, at least 2.45-2.32 billion years ago, and probably much earlier. Geo-biological interpretation of Archean Eon sedimentary rocks remains a challenge; available evidence indicates that life existed 3.5 billion years ago, but the question of when oxygenic photosynthesis evolved continues to engender debate and research.
A clear paleontological window on cyanobacterial evolution opened about 2.0 billion years ago, revealing an already diverse biota of blue-greens. Cyanobacteria remained principal primary producers throughout the Proterozoic (2.5 Billion B.C.T. - 543 Million B.C.T.), in part because the redox structure of the oceans favored photoautotrophs capable of nitrogen fixation.
The most common cyanobacterial structures in the fossil record are the mound-producing stromatolites and related oncolites. Indeed, these fossil colonies are so common that paleobiology, micropaleontology and paleobotany cite the Pre-Cambrian and Cambrian period as an "age of stromatolites" and an "age of algae."
Green algae joined the blue-greens as major primary producers on continental shelves near the end of the Proterozoic, but only with the Mesozoic era (251 Million B.C.T. - 65 Million B.C.T.) radiations of dinoflagellates, coccolithophorids, and diatoms did primary production in marine shelf waters take modern form.
Today, the blue-green bacteria remain critical to marine ecosystems as primary producers in oceanic gyres, as agents of biological nitrogen fixation, and—in modified form—as the plastids of marine algae.
Monday, November 19, 2012
3.5. Billion B.C.T. - Photosynthesis Begins
It is believed that photosynthesis began around 3.5 billion years ago.
Photosynthesis (from the Greek photo, "light," and synthesis, "putting together", "composition") is a process used by plants and other organisms to convert the light energy captured from the sun into chemical energy that can be used to fuel the organism's activities. Photosynthesis occurs in plants, algae, and many species of bacteria, but not in archaea. Photosynthetic organisms are called photoautotrophs, since they can create their own food. In plants, algae, and cyanobacteria, photosynthesis uses carbon dioxide and water, releasing oxygen as a waste product.
Photosynthesis is vital for all aerobic life on Earth. In addition to maintaining normal levels of oxygen in the atmosphere, photosynthesis is the source of energy for nearly all life on earth, either directly, through primary production, or indirectly, as the ultimate source of the energy in their food, the exceptions being chemoautotrophs that live in rocks or around deep sea hydrothermal vents. The average rate of energy capture by photosynthesis globally is immense, approximately 130 terawatts, which is about six times larger than the power consumption of human civilization. As well as energy, photosynthesis is also the source of the carbon in all the organic compounds within organisms' bodies. In all, photosynthetic organisms convert around 100–115 thousand million metric tons (i.e., 100–115 petagrams) of carbon into biomass per year.
Although photosynthesis can happen in different ways in different species, some features are always the same. For example, the process always begins when energy from light is absorbed by proteins called photosynthetic reaction centers that contain chlorophylls. In plants, these proteins are held inside organelles called chloroplasts, while in bacteria they are embedded in the plasma membrane. Some of the light energy gathered by chlorophylls is stored in the form of adenosine triphosphate (ATP). The rest of the energy is used to remove electrons from a substance such as water. These electrons are then used in the reactions that turn carbon dioxide into organic compounds. In plants, algae and cyanobacteria, this is done by a sequence of reactions called the Calvin cycle, but different sets of reactions are found in some bacteria, such as the reverse Krebs cycle in Chlorobium. Many photosynthetic organisms have adaptations that concentrate or store carbon dioxide. This helps reduce a wasteful process called photorespiration that can consume part of the sugar produced during photosynthesis.
The first photosynthetic organisms probably evolved about 3.5 billion years ago, early in the evolutionary history of life, when all forms of life on Earth were microorganisms and the atmosphere had much more carbon dioxide. They most likely used hydrogen or hydrogen sulfide as sources of electrons, rather than water. Cyanobacteria appeared later, around 3.0 billion years ago, and drastically changed the Earth when they began to oxygenate the atmosphere, beginning about 2.4 billion years ago. This new atmosphere enabled the evolution of complex life such as protists. Eventually, no later than 1.0 billion years ago, one of these protists formed a symbiotic relationship with a cyanobacterium, producing the ancestor of many plants and algae. The chloroplasts in modern plants are the descendants of these ancient symbiotic cyanobacteria.
Photosynthesis (from the Greek photo, "light," and synthesis, "putting together", "composition") is a process used by plants and other organisms to convert the light energy captured from the sun into chemical energy that can be used to fuel the organism's activities. Photosynthesis occurs in plants, algae, and many species of bacteria, but not in archaea. Photosynthetic organisms are called photoautotrophs, since they can create their own food. In plants, algae, and cyanobacteria, photosynthesis uses carbon dioxide and water, releasing oxygen as a waste product.
Photosynthesis is vital for all aerobic life on Earth. In addition to maintaining normal levels of oxygen in the atmosphere, photosynthesis is the source of energy for nearly all life on earth, either directly, through primary production, or indirectly, as the ultimate source of the energy in their food, the exceptions being chemoautotrophs that live in rocks or around deep sea hydrothermal vents. The average rate of energy capture by photosynthesis globally is immense, approximately 130 terawatts, which is about six times larger than the power consumption of human civilization. As well as energy, photosynthesis is also the source of the carbon in all the organic compounds within organisms' bodies. In all, photosynthetic organisms convert around 100–115 thousand million metric tons (i.e., 100–115 petagrams) of carbon into biomass per year.
Although photosynthesis can happen in different ways in different species, some features are always the same. For example, the process always begins when energy from light is absorbed by proteins called photosynthetic reaction centers that contain chlorophylls. In plants, these proteins are held inside organelles called chloroplasts, while in bacteria they are embedded in the plasma membrane. Some of the light energy gathered by chlorophylls is stored in the form of adenosine triphosphate (ATP). The rest of the energy is used to remove electrons from a substance such as water. These electrons are then used in the reactions that turn carbon dioxide into organic compounds. In plants, algae and cyanobacteria, this is done by a sequence of reactions called the Calvin cycle, but different sets of reactions are found in some bacteria, such as the reverse Krebs cycle in Chlorobium. Many photosynthetic organisms have adaptations that concentrate or store carbon dioxide. This helps reduce a wasteful process called photorespiration that can consume part of the sugar produced during photosynthesis.
The first photosynthetic organisms probably evolved about 3.5 billion years ago, early in the evolutionary history of life, when all forms of life on Earth were microorganisms and the atmosphere had much more carbon dioxide. They most likely used hydrogen or hydrogen sulfide as sources of electrons, rather than water. Cyanobacteria appeared later, around 3.0 billion years ago, and drastically changed the Earth when they began to oxygenate the atmosphere, beginning about 2.4 billion years ago. This new atmosphere enabled the evolution of complex life such as protists. Eventually, no later than 1.0 billion years ago, one of these protists formed a symbiotic relationship with a cyanobacterium, producing the ancestor of many plants and algae. The chloroplasts in modern plants are the descendants of these ancient symbiotic cyanobacteria.
Friday, November 16, 2012
3.5 Billion B.C.T. - The First Primitive Life Forms Emerged
Around 3.5 Billion B.C.T., the first primitive life forms emerged on Earth. The fossil record contains prokaryotes (cells without nuclei) from up to 3.5 billion years ago, and eukaryotes (cells with nuclei) from up to 2.7 billion years ago.
The prokaryotes are a group of organisms whose cells lack a cell nucleus (karyon), or any other membrane-bound organelles. The organisms whose cells do have a nucleus are called eukaryotes. Most prokaryotes are unicellular organisms, although a few such as myxobacteria have multi-cellular stages in their life cycles or create large colonies like cyanobacteria. The word prokaryote comes from the Greek (pro-) "before" + (karyon) "nut or kernel".
Prokaryotes do not have a nucleus, mitochondria, or any other membrane-bound organelles. In other words, all their intra-cellular water-soluble components (proteins, DNA and metabolites) are located together in the same area enclosed by cell membrane, rather than separated in different cellular compartments.
The division to prokaryotes and eukaryotes reflects two distinct levels of cellular organization rather than biological classification of species. Prokaryotes include two major classification domains: the bacteria and the archaea. Archaea were recognized as a domain of life in 1990. These organisms were originally thought to live only in inhospitable conditions such as extremes of temperature, pH, and radiation but have since been found in all types of habitats.
The division to prokaryotes and eukaryotes is usually considered the most important distinction among organisms. The distinction is that eukaryotic cells have a "true" nucleus containing their DNA, whereas prokaryotic cells do not have a nucleus. One criticism of this classification points out that the word "prokaryote" is based on what these organisms are not (they are not eukaryotic), rather than what they are (either archaea or bacteria). Another difference is that ribosomes in prokaryotes are smaller than in eukaryotes. However, two organelles found in many eukaryotic cells, mitochondria and chloroplasts, contain ribosomes similar in size and makeup to those found in prokaryotes. This is one of many pieces of evidence that mitochondria and chloroplasts are themselves descended from free-living bacteria.
The genome in a prokaryote is held within a DNA/protein complex in the cytosol called the nucleoid, which lacks a nuclear envelope. The complex contains a single, cyclic, double-stranded molecule of stable chromosomal DNA, in contrast to the multiple linear, compact, highly organized chromosomes found in eukaryotic cells. In addition, many important genes of prokaryotes are stored in separate circular DNA structures called plasmids.
Prokaryotes lack distinct mitochondria and chloroplasts. Instead, processes such as oxidative phosphorylation and photosynthesis take place across the prokaryotic cell membrane. However, prokaryotes do possess some internal structures, such as prokaryotic cytoskeletons, and the bacterial order Planctomycetes have a membrane around their nucleoid and contain other membrane-bound cellular structures. Both eukaryotes and prokaryotes contain large RNA/protein structures called ribosomes, which produce protein.
Prokaryotic cells are usually much smaller than eukaryotic cells. Therefore, prokaryotes have a larger surface-area-to-volume ratio, giving them a higher metabolic rate, a higher growth rate, and, as a consequently, a shorter generation time than eukaryotes.
In 1977, Carl Woese proposed dividing prokaryotes into the bacteria and archaea (originally eubacteria and archaebacteria) because of the major differences in the structure and genetics between the two groups of organisms. This arrangement of eukaryota (also called "eukarya"), bacteria, and archaea is called the three-domain system, replacing the traditional two-empire system.
The oldest known fossilized prokaryotes were laid down approximately 3.5 billion years ago, only about 1 billion years after the formation of the Earth's crust. Even today, prokaryotes are perhaps the most successful and abundant life-forms. Eukaryotes only appear in the fossil record later, and may have formed from endosymbiosis of multiple prokaryote ancestors. The oldest known fossil eukaryotes are about 1.7 billion years old. However, some genetic evidence suggests eukaryotes appeared as early as 3 billion years ago.
While Earth is the only place in the universe where life is known to exist, some have suggested that there is evidence on Mars of fossil or living prokaryotes; but this possibility remains the subject of considerable debate and skepticism.
Prokaryotes have diversified greatly throughout their long existence. The metabolism of prokaryotes is far more varied than that of eukaryotes, leading to many highly distinct prokaryotic types. For example, in addition to using photosynthesis or organic compounds for energy, as eukaryotes do, prokaryotes may obtain energy from inorganic compounds such as hydrogen sulfide. This enables prokaryotes to thrive in harsh environments as cold as the snow surface of Antarctica, and as hot as undersea hydrothermal vents and land-based hot springs.
*****
A eukaryote is an organism whose cells contain complex structures enclosed within membranes. Eukaryotes may more formally be referred to as the taxon Eukarya or Eukaryota. The defining membrane-bound structure that sets eukaryotic cells apart from prokaryotic cells is the nucleus, or nuclear envelope, within which the genetic material is carried. The presence of a nucleus gives eukaryotes their name, which comes from the Greek eu ("good") and karyon ("nut" or "kernel"). Most eukaryotic cells also contain other membrane-bound organelles such as mitochondria, chloroplasts and the Golgi apparatus. All large complex organisms are eukaryotes, including animals, plants and fungi. The group also includes many unicellular organisms.
Cell division in eukaryotes is different from that in organisms without a nucleus (Prokaryote). It involves separating the duplicated chromosomes, through movements directed by microtubules. There are two types of division processes. In mitosis, one cell divides to produce two genetically identical cells. In meiosis, which is required in sexual reproduction, one diploid cell (a cell having two instances of each chromosome, one from each parent) undergoes recombination of each pair of parental chromosomes, and then two stages of cell division, resulting in four haploid cells (gametes). Each gamete has just one complement of chromosomes, each a unique mix of the corresponding pair of parental chromosomes.
Eukaryotes appear to be monophyletic, and thus make up one of the three domains of life. The two other domains, bacteria and archaea, are prokaryotes and have none of the above features. Eukaryotes represent a tiny minority of all living things; even in a human body there are 10 times more microbes than human cells. However, due to their much larger size their collective worldwide biomass is estimated at about equal to that of prokaryotes.
The origin of the eukaryotic cell is considered a milestone in the evolution of life, since they include all complex cells and almost all multicellular organisms. The timing of this series of events is hard to determine. Some acritarchs are known from at least 1.65 billion years ago, and the possible algae Grypania has been found as far back as 2.1 billion years ago.
Organized living structures have been found in black shales of the Palaeoproterozoic Francevillian B Formation in Gabon, dated at 2.1 billion years old. Eukaryotic life could have evolved at that time. Fossils that are clearly related to modern groups start appearing an estimated 1.2 billion years ago, in the form of a red algae, though recent work suggests the existence of fossilized filamentous algae in the Vindhya basin dating back perhaps to 1.6 to 1.7 billion years ago.
Biomarkers suggest that at least stem eukaryotes arose even earlier. The presence of steranes in Australian shales indicates that eukaryotes were present in these rocks dated at 2.7 billion years old.
The prokaryotes are a group of organisms whose cells lack a cell nucleus (karyon), or any other membrane-bound organelles. The organisms whose cells do have a nucleus are called eukaryotes. Most prokaryotes are unicellular organisms, although a few such as myxobacteria have multi-cellular stages in their life cycles or create large colonies like cyanobacteria. The word prokaryote comes from the Greek (pro-) "before" + (karyon) "nut or kernel".
Prokaryotes do not have a nucleus, mitochondria, or any other membrane-bound organelles. In other words, all their intra-cellular water-soluble components (proteins, DNA and metabolites) are located together in the same area enclosed by cell membrane, rather than separated in different cellular compartments.
The division to prokaryotes and eukaryotes reflects two distinct levels of cellular organization rather than biological classification of species. Prokaryotes include two major classification domains: the bacteria and the archaea. Archaea were recognized as a domain of life in 1990. These organisms were originally thought to live only in inhospitable conditions such as extremes of temperature, pH, and radiation but have since been found in all types of habitats.
The division to prokaryotes and eukaryotes is usually considered the most important distinction among organisms. The distinction is that eukaryotic cells have a "true" nucleus containing their DNA, whereas prokaryotic cells do not have a nucleus. One criticism of this classification points out that the word "prokaryote" is based on what these organisms are not (they are not eukaryotic), rather than what they are (either archaea or bacteria). Another difference is that ribosomes in prokaryotes are smaller than in eukaryotes. However, two organelles found in many eukaryotic cells, mitochondria and chloroplasts, contain ribosomes similar in size and makeup to those found in prokaryotes. This is one of many pieces of evidence that mitochondria and chloroplasts are themselves descended from free-living bacteria.
The genome in a prokaryote is held within a DNA/protein complex in the cytosol called the nucleoid, which lacks a nuclear envelope. The complex contains a single, cyclic, double-stranded molecule of stable chromosomal DNA, in contrast to the multiple linear, compact, highly organized chromosomes found in eukaryotic cells. In addition, many important genes of prokaryotes are stored in separate circular DNA structures called plasmids.
Prokaryotes lack distinct mitochondria and chloroplasts. Instead, processes such as oxidative phosphorylation and photosynthesis take place across the prokaryotic cell membrane. However, prokaryotes do possess some internal structures, such as prokaryotic cytoskeletons, and the bacterial order Planctomycetes have a membrane around their nucleoid and contain other membrane-bound cellular structures. Both eukaryotes and prokaryotes contain large RNA/protein structures called ribosomes, which produce protein.
Prokaryotic cells are usually much smaller than eukaryotic cells. Therefore, prokaryotes have a larger surface-area-to-volume ratio, giving them a higher metabolic rate, a higher growth rate, and, as a consequently, a shorter generation time than eukaryotes.
In 1977, Carl Woese proposed dividing prokaryotes into the bacteria and archaea (originally eubacteria and archaebacteria) because of the major differences in the structure and genetics between the two groups of organisms. This arrangement of eukaryota (also called "eukarya"), bacteria, and archaea is called the three-domain system, replacing the traditional two-empire system.
The oldest known fossilized prokaryotes were laid down approximately 3.5 billion years ago, only about 1 billion years after the formation of the Earth's crust. Even today, prokaryotes are perhaps the most successful and abundant life-forms. Eukaryotes only appear in the fossil record later, and may have formed from endosymbiosis of multiple prokaryote ancestors. The oldest known fossil eukaryotes are about 1.7 billion years old. However, some genetic evidence suggests eukaryotes appeared as early as 3 billion years ago.
While Earth is the only place in the universe where life is known to exist, some have suggested that there is evidence on Mars of fossil or living prokaryotes; but this possibility remains the subject of considerable debate and skepticism.
Prokaryotes have diversified greatly throughout their long existence. The metabolism of prokaryotes is far more varied than that of eukaryotes, leading to many highly distinct prokaryotic types. For example, in addition to using photosynthesis or organic compounds for energy, as eukaryotes do, prokaryotes may obtain energy from inorganic compounds such as hydrogen sulfide. This enables prokaryotes to thrive in harsh environments as cold as the snow surface of Antarctica, and as hot as undersea hydrothermal vents and land-based hot springs.
*****
A eukaryote is an organism whose cells contain complex structures enclosed within membranes. Eukaryotes may more formally be referred to as the taxon Eukarya or Eukaryota. The defining membrane-bound structure that sets eukaryotic cells apart from prokaryotic cells is the nucleus, or nuclear envelope, within which the genetic material is carried. The presence of a nucleus gives eukaryotes their name, which comes from the Greek eu ("good") and karyon ("nut" or "kernel"). Most eukaryotic cells also contain other membrane-bound organelles such as mitochondria, chloroplasts and the Golgi apparatus. All large complex organisms are eukaryotes, including animals, plants and fungi. The group also includes many unicellular organisms.
Cell division in eukaryotes is different from that in organisms without a nucleus (Prokaryote). It involves separating the duplicated chromosomes, through movements directed by microtubules. There are two types of division processes. In mitosis, one cell divides to produce two genetically identical cells. In meiosis, which is required in sexual reproduction, one diploid cell (a cell having two instances of each chromosome, one from each parent) undergoes recombination of each pair of parental chromosomes, and then two stages of cell division, resulting in four haploid cells (gametes). Each gamete has just one complement of chromosomes, each a unique mix of the corresponding pair of parental chromosomes.
Eukaryotes appear to be monophyletic, and thus make up one of the three domains of life. The two other domains, bacteria and archaea, are prokaryotes and have none of the above features. Eukaryotes represent a tiny minority of all living things; even in a human body there are 10 times more microbes than human cells. However, due to their much larger size their collective worldwide biomass is estimated at about equal to that of prokaryotes.
The origin of the eukaryotic cell is considered a milestone in the evolution of life, since they include all complex cells and almost all multicellular organisms. The timing of this series of events is hard to determine. Some acritarchs are known from at least 1.65 billion years ago, and the possible algae Grypania has been found as far back as 2.1 billion years ago.
Organized living structures have been found in black shales of the Palaeoproterozoic Francevillian B Formation in Gabon, dated at 2.1 billion years old. Eukaryotic life could have evolved at that time. Fossils that are clearly related to modern groups start appearing an estimated 1.2 billion years ago, in the form of a red algae, though recent work suggests the existence of fossilized filamentous algae in the Vindhya basin dating back perhaps to 1.6 to 1.7 billion years ago.
Biomarkers suggest that at least stem eukaryotes arose even earlier. The presence of steranes in Australian shales indicates that eukaryotes were present in these rocks dated at 2.7 billion years old.
Thursday, November 15, 2012
3.7 Billion B.C.T. - The Late Heavy Bombardment Ended
Around 3.7 Billion B.C.T., the Late Heavy Bombardment of the Earth came to an end.
The Late Heavy Bombardment (commonly referred to as the lunar cataclysm, or LHB) is a period of time approximately 4.1 to 3.7 billion years ago during which a large number of impact craters were formed on the Moon, and by inference on Earth, Mercury, Venus, and Mars as well. The LHB is "late" only in relation to the main period of accretion, when the Earth and the other three rocky planets first formed and gained most of their mass. In relation to the Earth or to Solar System history as a whole, it is still a fairly early phase. The evidence for this event comes primarily from the dating of lunar samples, which indicates that most impact melt rocks formed in this rather narrow interval of time. While many hypotheses have been put forth to explain a spike in the flux of either asteroidal or cometary materials in the inner Solar System, no consensus yet exists as to its cause. The Nice model, popular among planetary scientists, postulates that the gas giant planets underwent orbital migration at this time, scattering objects in the asteroid belt and/or Kuiper belt on eccentric orbits that crossed those of the terrestrial planets.
The Late Heavy Bombardment (commonly referred to as the lunar cataclysm, or LHB) is a period of time approximately 4.1 to 3.7 billion years ago during which a large number of impact craters were formed on the Moon, and by inference on Earth, Mercury, Venus, and Mars as well. The LHB is "late" only in relation to the main period of accretion, when the Earth and the other three rocky planets first formed and gained most of their mass. In relation to the Earth or to Solar System history as a whole, it is still a fairly early phase. The evidence for this event comes primarily from the dating of lunar samples, which indicates that most impact melt rocks formed in this rather narrow interval of time. While many hypotheses have been put forth to explain a spike in the flux of either asteroidal or cometary materials in the inner Solar System, no consensus yet exists as to its cause. The Nice model, popular among planetary scientists, postulates that the gas giant planets underwent orbital migration at this time, scattering objects in the asteroid belt and/or Kuiper belt on eccentric orbits that crossed those of the terrestrial planets.
3.7 Billion B.C.T. - Life Begins on Earth
Around 3.7 Billion B.C.T., life began on Earth.
Evidence suggests that life on Earth has existed for about 3.7 billion years, with the oldest traces of life found in fossils dating back 3.4 billion years. All known life forms share fundamental molecular mechanisms, reflecting their common descent; based on these observations, hypotheses on the origin of life attempt to find a mechanism explaining the formation of a universal common ancestor, from simple organic molecules via pre-cellular life to protocells and metabolism. Models have been divided into "genes-first" and "metabolism-first" categories, but a recent trend is the emergence of hybrid models that combine both categories.
There is no current scientific consensus as to how life originated. However, most accepted scientific models build on the following observations:
However, since genes and proteins are both required to produce the other, the problem of considering which came first is like that of the chicken or the egg. Most scientists have adopted the hypothesis that because of this, it is unlikely that genes and proteins arose independently.
A possibility, first suggested by Francis Crick, is that the first life was based on RNA, which has the DNA-like properties of information storage and the catalytic properties of some proteins. This is called the RNA world hypothesis, and it is supported by the observation that many of the most critical components of cells (those that evolve the slowest) are composed mostly or entirely of RNA. Also, many critical co-factors are either nucleotides or substances clearly related to them. The catalytic properties of RNA had not yet been demonstrated when the hypothesis was first proposed, but they were confirmed by Thomas Cech in 1986.
One issue with the RNA world hypothesis is that synthesis of RNA from simple inorganic precursors is more difficult than for other organic molecules. One reason for this is that RNA precursors are very stable and react with each other very slowly under ambient conditions, and it has also been proposed that living organisms consisted of other molecules before RNA. However, the successful synthesis of certain RNA molecules under the conditions that existed prior to life on Earth has been achieved by adding alternative precursors in a specified order with the precursor phosphate present throughout the reaction. This study makes the RNA world hypothesis more plausible.
In 2009, experiments demonstrated Darwinian evolution of a two-component system of RNA enzymes (ribozymes) in vitro. The work was performed in the laboratory of Gerald Joyce.
NASA findings in 2011, based on studies with meteorites found on Earth, suggest DNA and RNA components (adenine, guanine and related organic molecules) may be formed extraterrestrially in outer space.
Evidence suggests that life on Earth has existed for about 3.7 billion years, with the oldest traces of life found in fossils dating back 3.4 billion years. All known life forms share fundamental molecular mechanisms, reflecting their common descent; based on these observations, hypotheses on the origin of life attempt to find a mechanism explaining the formation of a universal common ancestor, from simple organic molecules via pre-cellular life to protocells and metabolism. Models have been divided into "genes-first" and "metabolism-first" categories, but a recent trend is the emergence of hybrid models that combine both categories.
There is no current scientific consensus as to how life originated. However, most accepted scientific models build on the following observations:
- The Miller-Urey experiment, and the work of Sidney Fox, show that conditions on the primitive Earth favored chemical reactions that synthesize amino acids and other organic compounds from inorganic precursors.
- Phospholipids spontaneously form lipid bilayers, the basic structure of a cell membrane.
However, since genes and proteins are both required to produce the other, the problem of considering which came first is like that of the chicken or the egg. Most scientists have adopted the hypothesis that because of this, it is unlikely that genes and proteins arose independently.
A possibility, first suggested by Francis Crick, is that the first life was based on RNA, which has the DNA-like properties of information storage and the catalytic properties of some proteins. This is called the RNA world hypothesis, and it is supported by the observation that many of the most critical components of cells (those that evolve the slowest) are composed mostly or entirely of RNA. Also, many critical co-factors are either nucleotides or substances clearly related to them. The catalytic properties of RNA had not yet been demonstrated when the hypothesis was first proposed, but they were confirmed by Thomas Cech in 1986.
One issue with the RNA world hypothesis is that synthesis of RNA from simple inorganic precursors is more difficult than for other organic molecules. One reason for this is that RNA precursors are very stable and react with each other very slowly under ambient conditions, and it has also been proposed that living organisms consisted of other molecules before RNA. However, the successful synthesis of certain RNA molecules under the conditions that existed prior to life on Earth has been achieved by adding alternative precursors in a specified order with the precursor phosphate present throughout the reaction. This study makes the RNA world hypothesis more plausible.
In 2009, experiments demonstrated Darwinian evolution of a two-component system of RNA enzymes (ribozymes) in vitro. The work was performed in the laboratory of Gerald Joyce.
NASA findings in 2011, based on studies with meteorites found on Earth, suggest DNA and RNA components (adenine, guanine and related organic molecules) may be formed extraterrestrially in outer space.
Wednesday, November 14, 2012
3.8 Billion B.C.T. - The Archean Eon Begins
Around 3.8 Billion B.C.T., the Archean Eon began.
The Archean (also spelled Archaean) is a geologic eon before the Proterozoic Eon, before 2.5 billion years ago. The Archean era is generally agreed to have started at 3.8 billion years ago, but this boundary is informal.
If you were able to travel back to visit the Earth during the Archean Eon, you would likely not recognize it as the same planet we inhabit today. The atmosphere was very different from what we breathe today. At that time, it was likely a reducing atmosphere of methane, ammonia, and other gases which would be toxic to most life on our planet today. Also, during this time, the Earth's crust cooled enough that rocks and continental plates began to form.
It was early in the Archean that life first appeared on Earth. Our oldest fossils date to roughly 3.5 billion years ago, and consist of bacteria microfossils. In fact, all life during the more than one billion years of the Archean was bacterial. The Archean coast was home to mounded colonies of photosynthetic bacteria called stromatolites. Stromatolites have been found as fossils in early Archean rocks of South Africa and western Australia. Stromatolites increased in abundance throughout the Archean, but began to decline during the Proterozoic. They are not common today, but they can still be found in Shark Bay, Australia.
The Archean (also spelled Archaean) is a geologic eon before the Proterozoic Eon, before 2.5 billion years ago. The Archean era is generally agreed to have started at 3.8 billion years ago, but this boundary is informal.
If you were able to travel back to visit the Earth during the Archean Eon, you would likely not recognize it as the same planet we inhabit today. The atmosphere was very different from what we breathe today. At that time, it was likely a reducing atmosphere of methane, ammonia, and other gases which would be toxic to most life on our planet today. Also, during this time, the Earth's crust cooled enough that rocks and continental plates began to form.
It was early in the Archean that life first appeared on Earth. Our oldest fossils date to roughly 3.5 billion years ago, and consist of bacteria microfossils. In fact, all life during the more than one billion years of the Archean was bacterial. The Archean coast was home to mounded colonies of photosynthetic bacteria called stromatolites. Stromatolites have been found as fossils in early Archean rocks of South Africa and western Australia. Stromatolites increased in abundance throughout the Archean, but began to decline during the Proterozoic. They are not common today, but they can still be found in Shark Bay, Australia.
Tuesday, November 13, 2012
4.0 Billion B.C.T. - A Meteor Struck Mars
Around 4 Billion B.C.T., conditions for the creation of life on Earth began to be maximized. Also, around this time, a meteor struck Mars.
When a meteor perhaps as large as a hundred miles in diameter smashed into Mars four billion years ago, the force of the impact re-contoured much of the southern Martian hemisphere. The collision punched a hole in the surface 1,300 miles across and 5 miles deep. The fallout of debris, enough to theoretically deposit a mile-thick layer across the continental United States, stretched 2,500 miles from the basin's center.
The Martian meteor impact of four billion years ago has a bearing on life on Earth because the debris from such impacts wound up landing on Earth and may possibly have contributed to the organic chemistry -- the chemistry of life -- that came to exist.
As of 2012, of the over 53,000 meteorites that have been found on Earth, 99 have been identified as Martian. These meteorites are thought to be from Mars because they have elemental and isotopic compositions that are similar to rocks and atmosphere gases analyzed by spacecraft on Mars.
Some planetary scientists think that the impact of asteroids and comets on Mars sent chunks of Martian rock hurtling into space, where they orbited the sun for millions of years. Finally, some of these bits of Mars came crashing down in Antarctica and other places on Earth. However, the impact on Mars some 4 billion years ago may have led to a more direct contribution of Martian materials to the milieu of what was then the nascent terraforming of Earth.
When a meteor perhaps as large as a hundred miles in diameter smashed into Mars four billion years ago, the force of the impact re-contoured much of the southern Martian hemisphere. The collision punched a hole in the surface 1,300 miles across and 5 miles deep. The fallout of debris, enough to theoretically deposit a mile-thick layer across the continental United States, stretched 2,500 miles from the basin's center.
The Martian meteor impact of four billion years ago has a bearing on life on Earth because the debris from such impacts wound up landing on Earth and may possibly have contributed to the organic chemistry -- the chemistry of life -- that came to exist.
As of 2012, of the over 53,000 meteorites that have been found on Earth, 99 have been identified as Martian. These meteorites are thought to be from Mars because they have elemental and isotopic compositions that are similar to rocks and atmosphere gases analyzed by spacecraft on Mars.
Some planetary scientists think that the impact of asteroids and comets on Mars sent chunks of Martian rock hurtling into space, where they orbited the sun for millions of years. Finally, some of these bits of Mars came crashing down in Antarctica and other places on Earth. However, the impact on Mars some 4 billion years ago may have led to a more direct contribution of Martian materials to the milieu of what was then the nascent terraforming of Earth.
Tuesday, November 6, 2012
4.56 Billion B.C.T. - The Hadean Eon Begins
Around 4.56 Billion Years B.C.T., the Hadean Eon began. During this period the Earth-Moon system would be formed.
The Hadean Eon is the first geologic eon of the Earth and lies before the Archean Eon. It began with the formation of the Earth about 4.56 billion years ago and ended roughly 3.8 billion years ago, though the latter date varies according to different sources. The name "Hadean" derives from Hades, the Greek name for the underworld. The name is in reference to the "hellish" conditions on Earth at the time: the planet had just formed and was still very hot due to high volcanism, a partially molten surface and frequent collisions with other Solar System bodies. The geologist Preston Cloud coined the term in 1972, originally to label the period before the earliest-known rocks on Earth.
The Moon is the only natural satellite of the Earth, and the fifth largest satellite in the Solar System. It is the largest natural satellite of a planet in the Solar System relative to the size of its primary, having 27% the diameter and 60% the density of Earth, resulting in 1⁄81 its mass. The Moon is the second densest satellite after Io, a satellite of Jupiter.
The Moon is in synchronous rotation with the Earth, always showing the same face with its near side marked by dark volcanic maria that fill between the bright ancient crustal highlands and the prominent impact craters. It is the brightest object in the sky after the Sun, although its surface is actually very dark, with a reflectance similar to that of coal. Its prominence in the sky and its regular cycle of phases have, since ancient times, made the Moon an important cultural influence on language, calendars, art and mythology. The Moon's gravitational influence produces the ocean tides and the minute lengthening of the day. The Moon's current orbital distance, about thirty times the diameter of the Earth, causes it to appear almost the same size in the sky as the Sun, allowing it to cover the Sun nearly precisely in total solar eclipses. This matching of apparent visual size is a coincidence. Earlier in the Earth's history, the Moon was closer to the Earth, and had an apparent visual size greater than that of the Sun.
The Moon is thought to have formed nearly 4.5 billion years ago, not long after the Earth. Although there have been several hypotheses for its origin in the past, the current most widely accepted explanation is that the Moon formed from the debris left over after a giant impact between Earth and a Mars-sized body. The Moon is the only celestial body other than the Earth on which humans have set foot. The Soviet Union's Luna programme was the first to reach the Moon with unmanned spacecraft in 1959; the United States' NASA Apollo program achieved the only manned missions to date, beginning with the first manned lunar orbiting mission by Apollo 8 in 1968, and six manned lunar landings between 1969 and 1972, with the first being Apollo 11. These missions returned over 380 kg of lunar rocks, which have been used to develop a geological understanding of the Moon's origins, the formation of its internal structure, and its subsequent history.
Although the Moon itself is devoid of air, water, and life, its creation and existence has proven to be essential to the origin of life on Earth. It is, after all, our unusually large moon which exerts a stabilizing influence on the Earth's spin axis that has prevented the planet from wobbling like an out-of-control top -- and has thereby saved the Earth from wild climate fluctuations that would have been hostile to life. Indeed, it is generally conceded that we, the inhabitants of the Earth, are in an exceptional state. We owe our very existence to the terrestrial stability caused by the nightly present Moon.
The tilt of the Earth's spin axis, called the obliquity, is what gives us seasons. If the Earth were spinning like a perfectly upright top, perpendicular to the plane of its orbit around the Sun (an obliquity of zero), there would hardly be any seasons at all because every point on the planet would receive a constant amount of sunlight all year long. However, if the Earth were rolling on its side (an obliquity of 90 degrees), each pole would swing between extreme heat and total darkness every year. Because the Earth's spin axis is only slightly tilted, by about 23.5 degrees, the planet enjoys moderate seasonal variations.
This slight tilt of the Earth's spin axis has been the case for eons and it has been so because of the Moon. Because the Earth spins, the planet bulges at the equator. The Sun and the other planets exert a gravitational pull on this bulge, causing the Earth's axis to rock slowly. As the planets move in their orbits -- and as they deform one another's orbits through their gravitational interactions -- the overall strength of the various forces would cause the Earth's spin axis to oscillate in an inherently unpredictable, chaotic way. Computer modeling indicates that the oscillation could vary anywhere from 0 to 85 degrees -- an amount that would make the possibility of life on Earth very unlikely.
However, with the Moon, chaos is averted and stability is imposed. The Moon packs enough gravitational pull to effectively cancel most of the other forces on the Earth's spin axis. With just a little help from the Sun, the Moon makes the Earth's axis settle into a regular motion, causing it to precess in a small circle every 26,000 years. The tilt of the axis does change over time, but only by 1.3 degrees instead of 85.
It is important to note that a mere one degree change in obliquity is not entirely harmless. Indeed, many scientists think that such a change could trigger an ice age. Given that such a traumatic climatic change could accompany only a minor oscillation, an obliquity that fluctuated by tens of degrees would have played havoc with the world's environment. The climate would have swung between epochs with extreme seasonal variations and epochs with none at all. Eco-systems would not have been able to stabilize long enough for advanced life forms such as humans to evolve.
It is now a generally accepted theory that the stability of the Earth's spin axis is a key to life. And as further proof of the validity of this theory, scientists point to Mars. Even though Mars currently tilts at a comfortable 25 degrees, that situation is probably temporary. Mars has only two Manhattan size satellites. Even together, these moons exert a puny gravitational force -- hardly enough to counteract other planetary influences.
The Hadean Eon is the first geologic eon of the Earth and lies before the Archean Eon. It began with the formation of the Earth about 4.56 billion years ago and ended roughly 3.8 billion years ago, though the latter date varies according to different sources. The name "Hadean" derives from Hades, the Greek name for the underworld. The name is in reference to the "hellish" conditions on Earth at the time: the planet had just formed and was still very hot due to high volcanism, a partially molten surface and frequent collisions with other Solar System bodies. The geologist Preston Cloud coined the term in 1972, originally to label the period before the earliest-known rocks on Earth.
The Moon is the only natural satellite of the Earth, and the fifth largest satellite in the Solar System. It is the largest natural satellite of a planet in the Solar System relative to the size of its primary, having 27% the diameter and 60% the density of Earth, resulting in 1⁄81 its mass. The Moon is the second densest satellite after Io, a satellite of Jupiter.
The Moon is in synchronous rotation with the Earth, always showing the same face with its near side marked by dark volcanic maria that fill between the bright ancient crustal highlands and the prominent impact craters. It is the brightest object in the sky after the Sun, although its surface is actually very dark, with a reflectance similar to that of coal. Its prominence in the sky and its regular cycle of phases have, since ancient times, made the Moon an important cultural influence on language, calendars, art and mythology. The Moon's gravitational influence produces the ocean tides and the minute lengthening of the day. The Moon's current orbital distance, about thirty times the diameter of the Earth, causes it to appear almost the same size in the sky as the Sun, allowing it to cover the Sun nearly precisely in total solar eclipses. This matching of apparent visual size is a coincidence. Earlier in the Earth's history, the Moon was closer to the Earth, and had an apparent visual size greater than that of the Sun.
The Moon is thought to have formed nearly 4.5 billion years ago, not long after the Earth. Although there have been several hypotheses for its origin in the past, the current most widely accepted explanation is that the Moon formed from the debris left over after a giant impact between Earth and a Mars-sized body. The Moon is the only celestial body other than the Earth on which humans have set foot. The Soviet Union's Luna programme was the first to reach the Moon with unmanned spacecraft in 1959; the United States' NASA Apollo program achieved the only manned missions to date, beginning with the first manned lunar orbiting mission by Apollo 8 in 1968, and six manned lunar landings between 1969 and 1972, with the first being Apollo 11. These missions returned over 380 kg of lunar rocks, which have been used to develop a geological understanding of the Moon's origins, the formation of its internal structure, and its subsequent history.
Although the Moon itself is devoid of air, water, and life, its creation and existence has proven to be essential to the origin of life on Earth. It is, after all, our unusually large moon which exerts a stabilizing influence on the Earth's spin axis that has prevented the planet from wobbling like an out-of-control top -- and has thereby saved the Earth from wild climate fluctuations that would have been hostile to life. Indeed, it is generally conceded that we, the inhabitants of the Earth, are in an exceptional state. We owe our very existence to the terrestrial stability caused by the nightly present Moon.
The tilt of the Earth's spin axis, called the obliquity, is what gives us seasons. If the Earth were spinning like a perfectly upright top, perpendicular to the plane of its orbit around the Sun (an obliquity of zero), there would hardly be any seasons at all because every point on the planet would receive a constant amount of sunlight all year long. However, if the Earth were rolling on its side (an obliquity of 90 degrees), each pole would swing between extreme heat and total darkness every year. Because the Earth's spin axis is only slightly tilted, by about 23.5 degrees, the planet enjoys moderate seasonal variations.
This slight tilt of the Earth's spin axis has been the case for eons and it has been so because of the Moon. Because the Earth spins, the planet bulges at the equator. The Sun and the other planets exert a gravitational pull on this bulge, causing the Earth's axis to rock slowly. As the planets move in their orbits -- and as they deform one another's orbits through their gravitational interactions -- the overall strength of the various forces would cause the Earth's spin axis to oscillate in an inherently unpredictable, chaotic way. Computer modeling indicates that the oscillation could vary anywhere from 0 to 85 degrees -- an amount that would make the possibility of life on Earth very unlikely.
However, with the Moon, chaos is averted and stability is imposed. The Moon packs enough gravitational pull to effectively cancel most of the other forces on the Earth's spin axis. With just a little help from the Sun, the Moon makes the Earth's axis settle into a regular motion, causing it to precess in a small circle every 26,000 years. The tilt of the axis does change over time, but only by 1.3 degrees instead of 85.
It is important to note that a mere one degree change in obliquity is not entirely harmless. Indeed, many scientists think that such a change could trigger an ice age. Given that such a traumatic climatic change could accompany only a minor oscillation, an obliquity that fluctuated by tens of degrees would have played havoc with the world's environment. The climate would have swung between epochs with extreme seasonal variations and epochs with none at all. Eco-systems would not have been able to stabilize long enough for advanced life forms such as humans to evolve.
It is now a generally accepted theory that the stability of the Earth's spin axis is a key to life. And as further proof of the validity of this theory, scientists point to Mars. Even though Mars currently tilts at a comfortable 25 degrees, that situation is probably temporary. Mars has only two Manhattan size satellites. Even together, these moons exert a puny gravitational force -- hardly enough to counteract other planetary influences.
It is estimated that the obliquity of Mars has probably varied between 0 and 60 degrees. That suggests a Martian history (and future) of wild climate fluctuations. Indeed, photographs of Mars' polar regions from the twin Viking orbiters reveal layers of ice and dust stacked unevenly like hotcakes -- a possible geologic record of the advance and retreat of the polar ice caps over hundreds of millions of years.
There are two implications of the association of the Moon with life on Earth that are quite profound. While planets like the Earth may well be abundant in the Universe, astronomers now concede that Earth-size planets with moons as large as ours are likely to be extremely rare. Thus, if a large moon is a prerequisite for the evolution of life, beings like us might turn out to be exceedingly rare as well.
The other implication is that the Earth can count on its stable climate only as long as it has a large moon nearby. However, the Moon, as a result of its gravitational interaction with the Earth, is gradually being accelerated into a higher orbit. The Moon is receding from the Earth at a rate of about one inch per year. In about one billion years, the pull of the Moon will be so weak that the Earth's obliquity will begin to fluctuate chaotically. When that happens the Earth's climate will surely undergo wild variations making life on the planet extremely difficult and probably impossible -- at least based upon our current perspective and upon the currently known abilities of the beings known as Homo sapiens.
There are two implications of the association of the Moon with life on Earth that are quite profound. While planets like the Earth may well be abundant in the Universe, astronomers now concede that Earth-size planets with moons as large as ours are likely to be extremely rare. Thus, if a large moon is a prerequisite for the evolution of life, beings like us might turn out to be exceedingly rare as well.
The other implication is that the Earth can count on its stable climate only as long as it has a large moon nearby. However, the Moon, as a result of its gravitational interaction with the Earth, is gradually being accelerated into a higher orbit. The Moon is receding from the Earth at a rate of about one inch per year. In about one billion years, the pull of the Moon will be so weak that the Earth's obliquity will begin to fluctuate chaotically. When that happens the Earth's climate will surely undergo wild variations making life on the planet extremely difficult and probably impossible -- at least based upon our current perspective and upon the currently known abilities of the beings known as Homo sapiens.
4.560 - 4.550 Billion Years B.C.T. – A Proto-Earth formed at the outer (cooler) edge of the habitable zone of the Solar System. At this stage the solar constant of the Sun was only about 73% of its current value, but liquid water may have existed on the surface of the Proto-Earth, probably due to the greenhouse warming of high levels of methane and carbon dioxide present in the atmosphere. The early bombardment began. Because the solar neighborhood is rife with large planetoids and debris, Earth experiences a number of giant impacts that help to increase its overall size.
4.533 Billion Years B.C.T. – The Precambrian, now termed a "supereon" but formerly an era, is split into three geological time intervals called eons: Hadean, Archaean and Proterozoic. The latter two are sub-divided into several eras as currently defined. In total, the Precambrian comprises some 85% of geological time from the formation of Earth to the time when creatures first developed exoskeletons (i.e., hard outer parts) and thereby left abundant fossil remains.
4.533 Billion Years B.C.T. – The Hadean Eon, Precambrian Supereon, and unofficial Cryptic era start as the Earth-Moon system forms, possibly as a result of a glancing collision between proto-Earth and the hypothetical protoplanet Theia (the Earth was considerably smaller than now, before this impact). This impact vaporized a large amount of the crust, and sent material into orbit around Earth, which lingered as rings, similar to those of Saturn, for a few million years, until they coalesced to become the Moon. The Moon geology pre-Nectarian period starts. Earth was covered by a magmatic ocean 200 kilometers (120 miles) deep resulting from the impact energy from this and other planetesimals during the early bombardment phase, and energy released by the planetary core forming. Outgassing from crustal rocks gives Earth a reducing atmosphere of methane, nitrogen, hydrogen, ammonia, and water vapor, with lesser amounts of hydrogen sulfide, carbon monoxide, then carbon dioxide. With further full outgassing over 1000–1500 K, nitrogen and ammonia become lesser constituents, and comparable amounts of methane, carbon monoxide, carbon dioxide, water vapor, and hydrogen are released.
4.5 Billion Years B.C.T. – The Sun entered a main sequence: a solar wind swept the Earth-Moon system clear of debris (mainly dust and gas). The end of the Early Bombardment Phase. The Basin Groups Era begins on Earth.
Basin Groups refers to 9 subdivisions of the lunar Pre-Nectarian geologic period. It is the second era of the Hadean.
The motivation for creating the Basin Groups subdivisions was to place 30 pre-Nectarian impact basins into 9 relative age groups. The relative age of the first basin in each group is based on crater densities and superposition relationships, whereas the other basins are included based on weaker grounds.[1] Basin Group 1 has no official age for its base, and the boundary between Basin Group 9 and the Nectarian period is defined by the formation of the Nectaris impact basin.
The age of the Nectaris basin is somewhat contentious, with the most frequently cited numbers placing it at 3.92 Ga, or more infrequently at 3.85 Ga.[2] Recently, however, it has been suggested that the Nectaris basin could be, in fact, much older and might have formed at ~4.1 Ga.[3] Basin Groups are not used as a geologic period on any of the United States Geological Survey lunar geologic maps. Basin Groups 1-9 and the earlier (informal) Cryptic era together make up the totality of the Pre-Nectarian period.
Since little or no geological evidence on Earth exists from the time spanned by the Pre-Nectarian period of the Moon, the Pre-Nectarian has been used as a guide by at least one notable scientific work[4] to subdivide the unofficial terrestrial Hadean eon. In particular, it is sometimes found that the Hadean eon is subdivided into the Cryptic era and Basin Groups 1-9 (which collectively make up the Pre-Nectarian), and the Nectarian and Lower Imbrian. The first lifeforms (self replicating RNA molecules, see RNA world hypothesis) may have evolved on earth around 4 bya during this era.
- c. 4,450 Ma – 100 million years after the Moon formed, the first lunar crust, formed of lunar anorthosite, differentiates from lower magmas. The earliest Earth crust probably forms similarly out of similar material. On Earth the pluvial period starts, in which the Earth's crust cools enough to let oceans form.
- c. 4,404 Ma – First known mineral, found at Jack Hills in Western Australia. Detrital zircons show presence of a solid crust and liquid water. Latest possible date for a secondary atmosphere to form, produced by the Earth's crust outgassing, reinforced by water and possibly organic molecules delivered by comet impacts and carbonaceous chondrites (including type CI shown to be high in a number of amino acids and polycyclic aromatic hydrocarbons (PAH)).
- c. 4,300 Ma – Nectarian Era begins on Earth.
- c. 4,250 Ma – Earliest evidence for life, based on unusually high amounts of light isotopes of carbon, a common sign of life, found in Earth's oldest mineral deposits located in the Jack Hills of Western Australia.[4]
- c. 4,100 Ma – Early Imbrian Era begins on Earth. Late heavy bombardment of the Moon (and probably of the Earth as well) by bolides and asteroids, produced possibly by the planetary migration of Neptune into the Kuiper belt as a result of orbital resonances between Jupiter and Saturn.[5] "Remains of biotic life" were found in 4.1 billion-year-old rocks in Western Australia.[6][7] According to one of the researchers, "If life arose relatively quickly on Earth ... then it could be common in the universe."[6]
Monday, November 5, 2012
4.6 Billion B.C.T. - The Kuiper Belt Forms
By 4.6 Billion Years B.C.T., the Kuiper Belt was formed.
The Kuiper Belt extends from just beyond the orbit of Neptune to a distance of about 50 astronomical units (4.65 billion miles) from the Sun. The Kuiper Belt is named for a Dutch-American astronomer, Gerald Kuiper, who predicted its existence in 1951, and it is the Kuiper Belt that has begun to provide the clues to answering the riddle of the solar system.
Astronomers had long theorized that many icy bodies orbit the sun beyond the planets. Astronomers predicted the existence of such objects based on a widely accepted theory that the planets in our solar system were formed from a rotating disk of gas and dust surrounding the infant sun. Theoretical models of solar system formation showed that beyond Neptune, small bodies, representing debris from the formation of the main planets, should exist. In addition, the motions of comets indicated that these small icy bodies originate far beyond the known planets.
Shortly after the beginning of the second millennium of the Christian calendar, many astronomers began to reassess the status of Pluto, the distant body that had been designated as the ninth planet. Astronomers noted that Pluto is more closely related to the Kuiper Belt objects than to the other planets. Pluto is far smaller than any other planet, and physically it is much more like a Kuiper Belt object or a large moon than a planet. Additionally, the orbit of Pluto is different from the other planets but is similar to other Kuiper Belt objects.
The reassessment of Pluto eventually led to it being "demoted" from being a planet. Indeed, other Kuiper Belt discoveries has led to the listing of Pluto with fellow Kuiper Belt objects, Haumea and Makemake, as being dwarf planets. Indeed, since the belt was discovered in 1992, the number of known Kuiper Belt objects (KBOs) has increased to over a thousand, and more than 100,000 KBOs over 100 km (62 mi) in diameter are believed to exist. The Kuiper Belt was initially thought to be the main repository for periodic comets, those with orbits lasting less than 200 years. However, studies since the mid-1990s have shown that the classical belt is dynamically stable, and that comets' true place of origin is the scattered disc, a dynamically active zone created by the outward motion of Neptune 4.5 billion years ago. Scattered disc objects such as Eris have extremely eccentric orbits that take them as far as 100 AU (9.3 billion miles) from the Sun.
Today, Pluto is the largest known member of the Kuiper belt. Originally considered a planet, Pluto's status as part of the Kuiper Belt caused it to be reclassified as a "dwarf planet" in 2006. It is compositionally similar to many other objects of the Kuiper Belt, and its orbital period is characteristic of a class of KBOs known as "plutinos".
Astronomers are fascinated by Kuiper Belt objects because they are cosmic leftovers, material that is virtually unchanged from the time when the sun and planets formed, about 4.6 billion years ago. By studying the Kuiper Belt, astronomers expect to learn much about the early solar system and how it came to be.
The Kuiper Belt extends from just beyond the orbit of Neptune to a distance of about 50 astronomical units (4.65 billion miles) from the Sun. The Kuiper Belt is named for a Dutch-American astronomer, Gerald Kuiper, who predicted its existence in 1951, and it is the Kuiper Belt that has begun to provide the clues to answering the riddle of the solar system.
Astronomers had long theorized that many icy bodies orbit the sun beyond the planets. Astronomers predicted the existence of such objects based on a widely accepted theory that the planets in our solar system were formed from a rotating disk of gas and dust surrounding the infant sun. Theoretical models of solar system formation showed that beyond Neptune, small bodies, representing debris from the formation of the main planets, should exist. In addition, the motions of comets indicated that these small icy bodies originate far beyond the known planets.
Shortly after the beginning of the second millennium of the Christian calendar, many astronomers began to reassess the status of Pluto, the distant body that had been designated as the ninth planet. Astronomers noted that Pluto is more closely related to the Kuiper Belt objects than to the other planets. Pluto is far smaller than any other planet, and physically it is much more like a Kuiper Belt object or a large moon than a planet. Additionally, the orbit of Pluto is different from the other planets but is similar to other Kuiper Belt objects.
The reassessment of Pluto eventually led to it being "demoted" from being a planet. Indeed, other Kuiper Belt discoveries has led to the listing of Pluto with fellow Kuiper Belt objects, Haumea and Makemake, as being dwarf planets. Indeed, since the belt was discovered in 1992, the number of known Kuiper Belt objects (KBOs) has increased to over a thousand, and more than 100,000 KBOs over 100 km (62 mi) in diameter are believed to exist. The Kuiper Belt was initially thought to be the main repository for periodic comets, those with orbits lasting less than 200 years. However, studies since the mid-1990s have shown that the classical belt is dynamically stable, and that comets' true place of origin is the scattered disc, a dynamically active zone created by the outward motion of Neptune 4.5 billion years ago. Scattered disc objects such as Eris have extremely eccentric orbits that take them as far as 100 AU (9.3 billion miles) from the Sun.
Today, Pluto is the largest known member of the Kuiper belt. Originally considered a planet, Pluto's status as part of the Kuiper Belt caused it to be reclassified as a "dwarf planet" in 2006. It is compositionally similar to many other objects of the Kuiper Belt, and its orbital period is characteristic of a class of KBOs known as "plutinos".
Astronomers are fascinated by Kuiper Belt objects because they are cosmic leftovers, material that is virtually unchanged from the time when the sun and planets formed, about 4.6 billion years ago. By studying the Kuiper Belt, astronomers expect to learn much about the early solar system and how it came to be.
4.57 Billion Years B.C.T. – A supernova explosion (known as the primal supernova) seeds our galactic neighborhood with heavy elements that will be incorporated into the Earth, and results in a shock wave in a dense region of the Milky Way galaxy. The Ca-Al-rich inclusions, which formed 2 million years before the chondrules, are a key signature of a supernova explosion.
4.567 Billion Years B.C.T. – A rapid collapse of hydrogen molecular cloud h, forming a third-generation Population I star, the Sun, in a region of the Galactic Habitable Zone (GHZ), about 25,000 light years from the center of the Milky Way Galaxy.
4.566 Billion Years B.C.T. – A protoplanetary disc (from which Earth eventually forms) emerges around the young Sun, which is in its T Tauri stage.
Saturday, November 3, 2012
5 Billion B.C.T. - Our Solar System Begins to Form
Around 5 Billion B.C.T., our solar system began to take shape.
One of the great beauties of all creation -- one of the great beauties of the universe -- is the solar system in which we live. By the end of the second millennium of the Christian calendar, scientists had begun to marvel at the unique quality of our solar system. Although other worlds have been discovered, and while other solar systems have been examined, none of the planets or solar systems matches the delicate machinery that is associated with our Earth and our solar system.
What makes our solar system so unique is that instead of having the planets orbit the sun in egg-shaped orbits much like the comets do, the planets of our solar system orbit the sun in neatly stacked, circular orbits. Scientists generally acknowledge that the presence of a circular orbit made possible the existence of life, as we know it, on this Earth. The relatively circular orbit of our Earth provided nearly equal temperatures all year round. In other words, it was the unique circular orbit of our earth that created a stable temperature and climate which facilitated the development of life.
Temperatures and climate would be much more volatile and life as we know it could not have survived if the Earth had had an elliptical orbit. Indeed, if the Jupiter of our solar system did not itself have a relatively circular orbit, it is doubtful that our Earth itself would even exist.
In the "light" of this precious realization, today, there is much, so very much to be thankful for, not the least of which is the fact that, on any given night, we can look up and view the beauty of the planets of our solar system; we can marvel at the mystery of how the planets and the solar system came to be; and we can feel blessed that the planets and their unique motion continue to watch over us all.
One of the great beauties of all creation -- one of the great beauties of the universe -- is the solar system in which we live. By the end of the second millennium of the Christian calendar, scientists had begun to marvel at the unique quality of our solar system. Although other worlds have been discovered, and while other solar systems have been examined, none of the planets or solar systems matches the delicate machinery that is associated with our Earth and our solar system.
What makes our solar system so unique is that instead of having the planets orbit the sun in egg-shaped orbits much like the comets do, the planets of our solar system orbit the sun in neatly stacked, circular orbits. Scientists generally acknowledge that the presence of a circular orbit made possible the existence of life, as we know it, on this Earth. The relatively circular orbit of our Earth provided nearly equal temperatures all year round. In other words, it was the unique circular orbit of our earth that created a stable temperature and climate which facilitated the development of life.
Temperatures and climate would be much more volatile and life as we know it could not have survived if the Earth had had an elliptical orbit. Indeed, if the Jupiter of our solar system did not itself have a relatively circular orbit, it is doubtful that our Earth itself would even exist.
In the "light" of this precious realization, today, there is much, so very much to be thankful for, not the least of which is the fact that, on any given night, we can look up and view the beauty of the planets of our solar system; we can marvel at the mystery of how the planets and the solar system came to be; and we can feel blessed that the planets and their unique motion continue to watch over us all.
8 Billion B.C.T. - The Expansion Speeds Up
Around 8 Billion B.C.T., the expansion of our universe began to speed up.
Friday, November 2, 2012
12.5 Billion B.C.T. - The First Galactic Habitable Zones Were Formed
The "habitable zones" of the first galaxies began to be formed.
The Earth occupies a privileged position within the solar system. If the Earth had been located much closer to the Sun, then, like Venus, it would have been too hot to support life. If the Earth had been located slightly farther from the Sun, then, like Mars, the Earth would have been too cold to sustain life. Our Earth sits in a so-called "habitable zone," a ring around the Sun within which liquid water can exist on a planet. Without liquid water, any kind of life as we know it is highly unlikely.
Scientists now posit that just as our solar system has a "habitable zone" so too do entire galaxies. Although most galaxies contain millions of stars, many of these stars appear to be located in uninhabitable zones. Scientists theorize that the habitable zone of a spiral galaxy (like our own Milky Way) may encircle its center, just as the habitable zone of the solar system encircles the Sun. Inside or outside this band, the galaxy is sterile and life cannot exist.
The question that arises is why? It is easy enough to understand why a single star should have a habitable zone, but it is not so easy to understand why a galaxy should have a habitable zone.
In response, scientists note that it is a delicate matter to make a planet like our Earth. To make an Earth, you need the right materials: heavy, rock-forming elements like silicon and aluminum, and iron for the core. At our location in the Milky Way, these elements are fairly abundant, but farther out, these elements become scarcer, and corollarily any existing rocky planets would tend to be smaller. These planets would also be cooler because there would be less of the heavy radioactive elements, that in the case of the Earth, warm up the interior by radioactive decay.
Without a warm interior, an Earth-like planet cannot have plate tectonics -- the gradual movement of the planet crust. This means that the planet cannot keep water circulating through its atmosphere, and so it is likely to run down to a frozen state. That is what happened to Mars. Mars is actually within the solar system's habitable zone, but Mars froze because, being smaller than Earth, it cooled down too quickly and lost the ability to maintain plate tectonics.
In contrast, further in towards the center of a spiral galaxy -- such as our Milky Way -- other factors frustrate the development of life. Stars are more densely crowded together, and so conditions would be stormier. Exploding stars -- "super novae", for instance -- may bathe nearby planetary systems in hazardous radiation. Additionally, planets are likely to suffer heavier bombardment by comets, which are sent charging through a star's planetary system by the gravitational pull of other stars. On Earth, the deadly effects of gigantic comet collisions may have choked life several times, thereby delaying the evolution of complex organisms. If this bombardment had been more frequent, life might never have taken hold at all, or it may have been constantly prevented from evolving into complex forms.
Based on these observations and conjectures, scientists suggest that most galaxies might have only limited regions where Earth-like planets could both form at all and be able to support life. Indeed, it may be that because many galaxies have less heavy elements than the Milky Way, their habitable zones might shrink out of existence, leaving no room for life.
In the final analysis, it may be that all that glitters is not gold -- that the Universe is likely filled with millions of galaxies with billions of solar systems, ... all of which are as barren and sterile as our Moon.
The Earth occupies a privileged position within the solar system. If the Earth had been located much closer to the Sun, then, like Venus, it would have been too hot to support life. If the Earth had been located slightly farther from the Sun, then, like Mars, the Earth would have been too cold to sustain life. Our Earth sits in a so-called "habitable zone," a ring around the Sun within which liquid water can exist on a planet. Without liquid water, any kind of life as we know it is highly unlikely.
Scientists now posit that just as our solar system has a "habitable zone" so too do entire galaxies. Although most galaxies contain millions of stars, many of these stars appear to be located in uninhabitable zones. Scientists theorize that the habitable zone of a spiral galaxy (like our own Milky Way) may encircle its center, just as the habitable zone of the solar system encircles the Sun. Inside or outside this band, the galaxy is sterile and life cannot exist.
The question that arises is why? It is easy enough to understand why a single star should have a habitable zone, but it is not so easy to understand why a galaxy should have a habitable zone.
In response, scientists note that it is a delicate matter to make a planet like our Earth. To make an Earth, you need the right materials: heavy, rock-forming elements like silicon and aluminum, and iron for the core. At our location in the Milky Way, these elements are fairly abundant, but farther out, these elements become scarcer, and corollarily any existing rocky planets would tend to be smaller. These planets would also be cooler because there would be less of the heavy radioactive elements, that in the case of the Earth, warm up the interior by radioactive decay.
Without a warm interior, an Earth-like planet cannot have plate tectonics -- the gradual movement of the planet crust. This means that the planet cannot keep water circulating through its atmosphere, and so it is likely to run down to a frozen state. That is what happened to Mars. Mars is actually within the solar system's habitable zone, but Mars froze because, being smaller than Earth, it cooled down too quickly and lost the ability to maintain plate tectonics.
In contrast, further in towards the center of a spiral galaxy -- such as our Milky Way -- other factors frustrate the development of life. Stars are more densely crowded together, and so conditions would be stormier. Exploding stars -- "super novae", for instance -- may bathe nearby planetary systems in hazardous radiation. Additionally, planets are likely to suffer heavier bombardment by comets, which are sent charging through a star's planetary system by the gravitational pull of other stars. On Earth, the deadly effects of gigantic comet collisions may have choked life several times, thereby delaying the evolution of complex organisms. If this bombardment had been more frequent, life might never have taken hold at all, or it may have been constantly prevented from evolving into complex forms.
Based on these observations and conjectures, scientists suggest that most galaxies might have only limited regions where Earth-like planets could both form at all and be able to support life. Indeed, it may be that because many galaxies have less heavy elements than the Milky Way, their habitable zones might shrink out of existence, leaving no room for life.
In the final analysis, it may be that all that glitters is not gold -- that the Universe is likely filled with millions of galaxies with billions of solar systems, ... all of which are as barren and sterile as our Moon.
12.7 Billion B.C.T. - The Cosmic Dark Ages End
The Cosmic Dark Ages came to an end as the first stars were formed. After a billion years of darkness, there was light.
13.2 Billion B.C.T. - The Galaxies Begin to Form
The galaxies began to form out of gaseous clouds of hydrogen and helium.
Thursday, November 1, 2012
13.8 Billion B.C.T. - The Big Bang or the Great Creation?
At the beginning of the third millennium of the Christian calendar -- at the beginning of the 21st century -- it was believed by most of the scientific community that our universe began some 13.8 billion years ago with the "big bang."
The commonly accepted model of the universe suggests that it began in an infinitely compact and singular state, enclosing a space even smaller than an atomic particle. The beginning of our universe then occurred when the compact particle -- the singularity -- grew not in a violent explosion (a "big bang") but rather through an incredibly rapid expansion -- an expansion so rapid that one could almost envision it as being a "creation."
While today scientists may feel relatively secure with the notion that the incredible expansion did occur, what they are not so secure about are some of the more troubling aspects surrounding the "scientific" explanations for how the incredible expansion occurred. Although the basic framework of the incredible expansion model has achieved wide acceptance, along with this acceptance has come an increased sophistication with regards to its shortcomings. As the potential for actually obtaining answers has improved, the questions have evolved from the "whats" and "wheres" to the "hows" and "whys".
Time, as we know it, began.
Up to 10–43 seconds after the Big Bang, the Planck Epoch began.
The Planck epoch is an era in traditional (non-inflationary) big bang cosmology in which the temperature is high enough that the four fundamental forces -- electromagnetism, gravitation, weak nuclear interaction, and strong nuclear interaction -- are all unified in one fundamental force. Little is understood about physics at this temperature, and different theories propose different scenarios. Traditional big bang cosmology predicts a gravitational singularity before this time, but this theory is based on general relativity and is expected to break down due to quantum effects. Physicists hope that proposed theories of quantum gravitation, such as string theory, loop quantum gravity, and causal sets, will eventually lead to a better understanding of this epoch.
In inflationary cosmology, times prior to the end of inflation (roughly 10−32 seconds after the Big Bang) do not follow the traditional big bang timeline. The universe before the end of inflation is a near-vacuum with a very low temperature, and persists for much longer than 10−32 second. Times from the end of inflation are based on the big bang time of the non-inflationary big bang model, not on the actual age of the universe at that time, which cannot be determined in inflationary cosmology. Thus, in inflationary cosmology there is no Planck epoch in the traditional sense, though similar conditions may have prevailed in a pre-inflationary era of the universe.
Between 10–43 seconds and 10–36 seconds after the Big Bang, the Grand Unification Epoch began.
As the universe expanded and cooled, it crossed transition temperatures at which forces separated from each other. These were phase transitions much like condensation and freezing. The grand unification epoch begins when gravitation separates from the other forces of nature, which are collectively known as gauge forces. The non-gravitational physics in this epoch would be described by a so-called grand unified theory (GUT). The grand unification epoch ends when the GUT forces further separate into the strong and electroweak forces. This transition should produce magnetic monopoles in large quantities, which are not observed. The lack of magnetic monopoles was one problem solved by the introduction of inflation.
In modern inflationary cosmology, the traditional grand unification epoch, like the Planck epoch, does not exist, though similar conditions likely would have existed in the universe prior to inflation.
Three forces began operating: electromagnetic, strong nuclear, and gravitational.
Weak interaction and electromagnetic force separated.
Between 10−36 seconds after the Big Bang to sometime between 10−33 and 10−32 seconds, the universe inflated at a rate faster than the speed of light.
The creative expansion of the universe was not an explosion in the classic sense. In our human experience with explosions, shrapnel like objects fly through a pre-existing space. However, with the expansion of the initial singularity, space itself was being created at the same time that time, matter, and even gravity were being formed. Indeed, at its beginning, the expansion of the singularity caused space to expand at speeds that, at times, exceeded the speed of light. This was possible because while light, energy and matter cannot exceed the speed of light, the expansion (the "creation") of space itself was not so restricted.
In physical cosmology, cosmic inflation, cosmological inflation or just inflation is the theorized extremely rapid exponential expansion of the early universe by a factor of at least 1078 in volume, driven by a negative-pressure vacuum energy density. The inflationary epoch comprises the first part of the electroweak epoch following the grand unification epoch. It lasted from 10−36 seconds after the Big Bang to sometime between 10−33 and 10−32 seconds. Following the inflationary period, the universe continued to expand, but at a slower rate.
The term "inflation" is also used to refer to the hypothesis that inflation occurred, to the theory of inflation, or to the inflationary epoch. The inflationary hypothesis was originally proposed in 1980 by American physicist Alan Guth, who named it "inflation". It was also proposed by Katsuhiko Sato in 1981.
As a direct consequence of this expansion, all of the observable universe originated in a small causally connected region. Inflation answers the classic conundrum of the Big Bang cosmology: why does the universe appear flat, homogeneous, and isotropic in accordance with the cosmological principle when one would expect, on the basis of the physics of the Big Bang, a highly curved, heterogeneous universe? Inflation also explains the origin of the large-scale structure of the cosmos. Quantum fluctuations in the microscopic inflationary region, magnified to cosmic size, become the seeds for the growth of structure in the universe.
While the detailed particle physics mechanism responsible for inflation is not known, the basic picture makes a number of predictions that have been confirmed by observation. Inflation is thus now considered part of the standard hot Big Bang cosmology. The hypothetical particle or field thought to be responsible for inflation is called the inflaton.
Quarks combined to form particles, including the "God" particle.
The Higgs boson or Higgs particle is an elementary particle initially theorised in 1964, and tentatively confirmed to exist on March 14, 2013. The discovery has been called "monumental" because it appears to confirm the existence of the Higgs field, which is pivotal to the Standard Model and other theories within particle physics, where it explains why some fundamental particles have mass when the symmetries controlling their interactions should require them to be massless, and—linked to this—why the weak force has a much shorter range than the electromagnetic force. Proof of its existence and measurement of its properties is expected to impact scientific knowledge across a range of fields, and should eventually allow physicists to determine whether the final unproven piece of the Standard Model or a competing theory is more likely to be correct, guide other theories and discoveries in particle physics, and—as with other fundamental discoveries of the past—potentially over time lead to developments in "new" physics, and new technologies.
The unanswered question ("Why do particles have mass?") in fundamental physics is of such importance that it led to a search of over 40 years for the Higgs boson and finally the construction of one of the most expensive and complex experimental facilities to date, the Large Hadron Collider able to create and study Higgs bosons and related questions. On July 4, 2012, a previously unknown particle was announced as being detected, which physicists suspected at the time to be the Higgs boson. By March 2013, the particle had been proven to behave, interact and decay in many of the expected ways predicted by the Standard Model, and was also tentatively confirmed to have + parity and zero spin, two fundamental criteria of a Higgs boson, making it also the first known scalar particle to be discovered in nature, although a number of other properties were not fully proven and some partial results do not yet precisely match those expected. As of March 2013 it is still uncertain whether its properties (when eventually known) will exactly match the predictions of the Standard Model, or whether additional Higgs bosons exist as predicted by some theories.
The Higgs boson is named after Peter Higgs, one of six physicists who, in 1964, proposed the mechanism that suggested the existence of such a particle. Although Higgs' name has become ubiquitous with this theory, the resulting electroweak model (the final outcome) involved several researchers between about 1960 and 1972, who each independently developed different parts. In mainstream media the Higgs boson is often referred to as the "God particle", from a 1993 book on the topic.
The nuclei of atoms formed.
The first true, complex atoms formed.
The commonly accepted model of the universe suggests that it began in an infinitely compact and singular state, enclosing a space even smaller than an atomic particle. The beginning of our universe then occurred when the compact particle -- the singularity -- grew not in a violent explosion (a "big bang") but rather through an incredibly rapid expansion -- an expansion so rapid that one could almost envision it as being a "creation."
While today scientists may feel relatively secure with the notion that the incredible expansion did occur, what they are not so secure about are some of the more troubling aspects surrounding the "scientific" explanations for how the incredible expansion occurred. Although the basic framework of the incredible expansion model has achieved wide acceptance, along with this acceptance has come an increased sophistication with regards to its shortcomings. As the potential for actually obtaining answers has improved, the questions have evolved from the "whats" and "wheres" to the "hows" and "whys".
Time, as we know it, began.
Up to 10–43 seconds after the Big Bang, the Planck Epoch began.
The Planck epoch is an era in traditional (non-inflationary) big bang cosmology in which the temperature is high enough that the four fundamental forces -- electromagnetism, gravitation, weak nuclear interaction, and strong nuclear interaction -- are all unified in one fundamental force. Little is understood about physics at this temperature, and different theories propose different scenarios. Traditional big bang cosmology predicts a gravitational singularity before this time, but this theory is based on general relativity and is expected to break down due to quantum effects. Physicists hope that proposed theories of quantum gravitation, such as string theory, loop quantum gravity, and causal sets, will eventually lead to a better understanding of this epoch.
In inflationary cosmology, times prior to the end of inflation (roughly 10−32 seconds after the Big Bang) do not follow the traditional big bang timeline. The universe before the end of inflation is a near-vacuum with a very low temperature, and persists for much longer than 10−32 second. Times from the end of inflation are based on the big bang time of the non-inflationary big bang model, not on the actual age of the universe at that time, which cannot be determined in inflationary cosmology. Thus, in inflationary cosmology there is no Planck epoch in the traditional sense, though similar conditions may have prevailed in a pre-inflationary era of the universe.
Between 10–43 seconds and 10–36 seconds after the Big Bang, the Grand Unification Epoch began.
Gravity separated from the three other forces: electromagnetic, strong nuclear, and weak interaction.
As the universe expanded and cooled, it crossed transition temperatures at which forces separated from each other. These were phase transitions much like condensation and freezing. The grand unification epoch begins when gravitation separates from the other forces of nature, which are collectively known as gauge forces. The non-gravitational physics in this epoch would be described by a so-called grand unified theory (GUT). The grand unification epoch ends when the GUT forces further separate into the strong and electroweak forces. This transition should produce magnetic monopoles in large quantities, which are not observed. The lack of magnetic monopoles was one problem solved by the introduction of inflation.
In modern inflationary cosmology, the traditional grand unification epoch, like the Planck epoch, does not exist, though similar conditions likely would have existed in the universe prior to inflation.
***
Three forces began operating: electromagnetic, strong nuclear, and gravitational.
Weak interaction and electromagnetic force separated.
Between 10−36 seconds after the Big Bang to sometime between 10−33 and 10−32 seconds, the universe inflated at a rate faster than the speed of light.
The creative expansion of the universe was not an explosion in the classic sense. In our human experience with explosions, shrapnel like objects fly through a pre-existing space. However, with the expansion of the initial singularity, space itself was being created at the same time that time, matter, and even gravity were being formed. Indeed, at its beginning, the expansion of the singularity caused space to expand at speeds that, at times, exceeded the speed of light. This was possible because while light, energy and matter cannot exceed the speed of light, the expansion (the "creation") of space itself was not so restricted.
In physical cosmology, cosmic inflation, cosmological inflation or just inflation is the theorized extremely rapid exponential expansion of the early universe by a factor of at least 1078 in volume, driven by a negative-pressure vacuum energy density. The inflationary epoch comprises the first part of the electroweak epoch following the grand unification epoch. It lasted from 10−36 seconds after the Big Bang to sometime between 10−33 and 10−32 seconds. Following the inflationary period, the universe continued to expand, but at a slower rate.
The term "inflation" is also used to refer to the hypothesis that inflation occurred, to the theory of inflation, or to the inflationary epoch. The inflationary hypothesis was originally proposed in 1980 by American physicist Alan Guth, who named it "inflation". It was also proposed by Katsuhiko Sato in 1981.
As a direct consequence of this expansion, all of the observable universe originated in a small causally connected region. Inflation answers the classic conundrum of the Big Bang cosmology: why does the universe appear flat, homogeneous, and isotropic in accordance with the cosmological principle when one would expect, on the basis of the physics of the Big Bang, a highly curved, heterogeneous universe? Inflation also explains the origin of the large-scale structure of the cosmos. Quantum fluctuations in the microscopic inflationary region, magnified to cosmic size, become the seeds for the growth of structure in the universe.
While the detailed particle physics mechanism responsible for inflation is not known, the basic picture makes a number of predictions that have been confirmed by observation. Inflation is thus now considered part of the standard hot Big Bang cosmology. The hypothetical particle or field thought to be responsible for inflation is called the inflaton.
***
Quarks combined to form particles, including the "God" particle.
The Higgs boson or Higgs particle is an elementary particle initially theorised in 1964, and tentatively confirmed to exist on March 14, 2013. The discovery has been called "monumental" because it appears to confirm the existence of the Higgs field, which is pivotal to the Standard Model and other theories within particle physics, where it explains why some fundamental particles have mass when the symmetries controlling their interactions should require them to be massless, and—linked to this—why the weak force has a much shorter range than the electromagnetic force. Proof of its existence and measurement of its properties is expected to impact scientific knowledge across a range of fields, and should eventually allow physicists to determine whether the final unproven piece of the Standard Model or a competing theory is more likely to be correct, guide other theories and discoveries in particle physics, and—as with other fundamental discoveries of the past—potentially over time lead to developments in "new" physics, and new technologies.
The unanswered question ("Why do particles have mass?") in fundamental physics is of such importance that it led to a search of over 40 years for the Higgs boson and finally the construction of one of the most expensive and complex experimental facilities to date, the Large Hadron Collider able to create and study Higgs bosons and related questions. On July 4, 2012, a previously unknown particle was announced as being detected, which physicists suspected at the time to be the Higgs boson. By March 2013, the particle had been proven to behave, interact and decay in many of the expected ways predicted by the Standard Model, and was also tentatively confirmed to have + parity and zero spin, two fundamental criteria of a Higgs boson, making it also the first known scalar particle to be discovered in nature, although a number of other properties were not fully proven and some partial results do not yet precisely match those expected. As of March 2013 it is still uncertain whether its properties (when eventually known) will exactly match the predictions of the Standard Model, or whether additional Higgs bosons exist as predicted by some theories.
The Higgs boson is named after Peter Higgs, one of six physicists who, in 1964, proposed the mechanism that suggested the existence of such a particle. Although Higgs' name has become ubiquitous with this theory, the resulting electroweak model (the final outcome) involved several researchers between about 1960 and 1972, who each independently developed different parts. In mainstream media the Higgs boson is often referred to as the "God particle", from a 1993 book on the topic.
***
The first picosecond (10−12) of cosmic time. It includes the Planck epoch, during which currently established laws of physics may not have applied; the emergence in stages of the four known fundamental interactions or forces -- first gravitation, and later the electromagnetic, weak and strong interactions; and the accelerated expansion of the universe due to cosmic inflation.
[In physical cosmology, cosmic inflation, cosmological inflation, or just inflation, is a theory of exponential expansion of space in the early universe. The inflationary epoch is believed to have lasted from 10−36 seconds to between 10−33 and 10−32 seconds after the Big Bang. Following the inflationary period, the universe continued to expand, but at a slower rate. The acceleration of this expansion due to dark energy began after the universe was already over 7.7 billion years old (5.4 billion years ago).
Inflation theory was developed in the late 1970s and early 80s, with notable contributions by several theoretical physicists, including Alexei Starobinsky at Landau Institute for Theoretical Physics, Alan Guth at Cornell University, and Andrei Linde at Lebedev Physical Institute. Alexei Starobinsky, Alan Guth, and Andrei Linde won the 2014 Kavli Prize "for pioneering the theory of cosmic inflation". It was developed further in the early 1980s. It explains the origin of the large-scale structure of the cosmos. Quantum fluctuatons in the microscopic inflationary region, magnified to cosmic size, become the seeds for the growth of structure in the Universe. Many physicists also believe that inflation explains why the universe appears to be the same in all directions (isotropic), why the cosmic microwave cosmic background radiation is distributed evenly, why the universe is flat, and why no magnetic monopoles have been observed.
The detailed particle physics mechanism responsible for inflation is unknown. The basic inflationary paradigm is accepted by most physicists, as a number of inflation model predictions have been confirmed by observation; however, a substantial minority of scientists dissent from this position. The hypothetical field thought to be responsible for inflation is called the inflaton.
In 2002, three of the original architects of the theory were recognized for their major contributions; physicists Alan Guth of M.I.T., Andrei Linde of Stanford, and Paul Steinhardt of Princeton shared the prestigious Dirac Prize "for development of the concept of inflation in cosmology". In 2012, Guth and Linde were awarded the Breakthrough Prize in Fundamental Physics for their invention and development of inflationary cosmology.]
Tiny ripples in the universe at this stage are believed to be the basis of large-scale structures that formed much later. Different stages of the very early universe are understood to different extents. The earlier parts are beyond the grasp of practical experiments in particle physics but can be explored through the extrapolation of known physical laws to extreme high temperatures.
***
The nuclei of atoms formed.
The first true, complex atoms formed.
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