542 Million B.C.T. - The Phanerozoic Eon Began

Around 542 Million B.C.T., the Phanerozoic Eon began. 

     The Phanerozoic Eon is the current geologic eon in the geologic timescale, and the one during which abundant animal life came to exist.  The Phanerozoic Eon covers roughly the last 542 million years and goes back to the time when diverse hard-shelled animals first appeared.  The name "Phanerozoic" derives from the ancient Greek words phaneros and zoic, meaning visible life, since it was once believed that life began in the Cambrian, the first period of the Phanerozoic Eon -- the first period of our current eon.  The time before the Phanerozoic, the time called the Precambrian supereon is now divided into the Hadean, Archaean and Proterozoic eons.

     The time span of the Phanerozoic includes the rapid emergence of a number of animal phyla; the evolution of these phyla into diverse forms; the development of complex plants; the evolution of fish; the emergence of terrestrial animals; and the development of modern faunas.  During this time span, tectonic forces caused the continents to move and eventually collect into a single landmass known as Pangaea, which then separated into the current continental landmasses.