Editing Phanerozoic (section)

==Proterozoic–Phanerozoic boundary==
{{Life timeline}}
The [[Proterozoic]]–Phanerozoic boundary is at 538.8&nbsp;million years ago.<ref name="ICS"/> In the 19th century, the boundary was set at time of appearance of the first abundant animal ([[metazoa]]n) [[fossil]]s, but [[trace fossil]]s of several hundred groups ([[taxon|taxa]]) of complex soft-bodied metazoa from the preceding [[Ediacaran]] period of the Proterozoic eon, known as the [[Avalon Explosion]], have been identified since the systematic study of those forms started in the 1950s.<ref>{{Cite journal| last=Glaessner |first=Martin F.| year=1961| title=Precambrian Animals| journal=Scientific American | volume=204| pages=72–78| doi=10.1038/scientificamerican0361-72| issue =3| bibcode=1961SciAm.204c..72G}}</ref><ref>{{cite journal |last1=Geyer |first1=Gerd |last2=Landing |first2=Ed |title=The Precambrian–Phanerozoic and Ediacaran–Cambrian boundaries: a historical approach to a dilemma |journal=Geological Society, London, Special Publications |year=2017 |volume=448 |issue=1 |pages=311–349 |doi=10.1144/SP448.10|bibcode=2017GSLSP.448..311G |s2cid=133538050 }}</ref> The transition from the [[Ediacaran biota|largely sessile Precambrian biota]] to the active mobile Cambrian biota occurred early in the Phanerozoic.