5 4 1 ▁million ) ▁e ons . ▁( There ▁is ▁only ▁one ▁other ▁e on : ▁the ▁Ph an ero zo ic , ▁ 5 4 1 ▁million - present .) ▁" P rec amb rian " ▁is ▁still ▁used ▁by ▁ge olog ists ▁and ▁pale ont olog ists ▁for ▁general ▁discuss ions ▁not ▁requiring ▁the ▁more ▁specific ▁e on ▁names . ▁, ▁the ▁United ▁States ▁Ge ological ▁Survey ▁cons iders ▁the ▁term ▁inform al , ▁lack ing ▁a ▁strat ig raph ic ▁rank . ▁ ▁Life ▁forms ▁ ▁A ▁specific ▁date ▁for ▁the ▁origin ▁of ▁life ▁has ▁not ▁been ▁determined . ▁Car bon ▁found ▁in ▁ 3 . 8 ▁billion - year - old ▁rocks ▁( Ar che an ▁e on ) ▁from ▁islands ▁off ▁western ▁Green land ▁may ▁be ▁of ▁organ ic ▁origin . ▁Well - pres erved ▁micro scop ic ▁foss ils ▁of ▁b acter ia ▁older ▁than ▁ 3 . 4 6 ▁billion ▁years ▁have ▁been ▁found ▁in ▁Western ▁Australia . ▁Pro b able ▁foss ils ▁ 1 0 0 ▁million ▁years ▁older ▁have ▁been ▁found ▁in ▁the ▁same ▁area . ▁However , ▁there ▁is ▁evidence ▁that ▁life ▁could ▁have ▁evol ved ▁over ▁ 4 . 2 8 0 ▁billion ▁years ▁ago . ▁There ▁is ▁a ▁fairly ▁solid ▁record ▁of ▁b acter ial ▁life ▁throughout ▁the ▁remainder ▁( Pro ter oz o ic ▁e on ) ▁of ▁the ▁P rec amb rian . ▁ ▁Ex cluding ▁a ▁few ▁cont ested ▁reports ▁of ▁much ▁older ▁forms ▁from ▁North ▁America