What is Phanerozoic?
The '''Phanerozoic''' [[eon]] is the current eon on the [[Historical geology#Table of geologic time|geologic timescale]]. It is the one in which abundant animal life has existed. It covers about 541 million years, and goes back to the time when hard-shelled animals first appeared. It was once thought that life began in the [[Cambrian]], the first [[Period (geology)|period]] of this eon. The time before the Phanerozoic, formerly called the ''[[Precambrian]]'', is now divided into the [[Hadean]], [[Archaean]] and [[Proterozoic]] eons. == Details == [[File:Phanerozoic Biodiversity.svg|400px|center|thumb|During the Phanerozoic the [[biodiversity]] shows a general increase from near zero to several thousands of genera.]] The exact time of the boundary between the Phanerozoic and the Proterozoic is slightly uncertain. In the 19th century, the boundary was set at the first abundant [[metazoa]]n [[fossil]]s. But several hundred kinds of [[Proterozoic]] [[metazoa]] have been discovered in the [[Ediacaran]]. Study of the [[Ediacaran biota]] started in the 1950s. There are three dividing points at the Proterozoic-Phanerozoic boundary. It might be where the first [[trilobite]]s and [[archaeocyatha]] appear; or at the first appearance of signs of burrowing; or at the first appearance of the '[[small shelly fauna]]'. The three different dividing points are within a few million years of each other. In the Phanerozoic [[biodiversity]] increased hugely: <ref> Markov A. & Korotayev A. 2008. Phanerozoic marine biodiversity follows a hyperbolic trend. ''Science Direct''. [http://www.sciencedirect.com/science/article/pii/S1871174X07000030]</ref><ref>Miller K.G. ''et al'' 2005. The Phanerozoic record of global sea-level change. ''Science'' '''310''' (5752): 1293–1298. [http://www.sciencemag.org/content/310/5752/1293]</ref> #the rapid emergence of animal [[Phylum (biology)|phyla]]; #the [[evolution]] of these phyla into diverse forms; #the emergence of terrestrial [[plant]]s; #the development of complex plants; #the evolution o