e . g . ▁st rom atol ites ) ▁are ▁of ▁limited ▁bi ost rat ig raph ic ▁use . ▁This ▁is ▁because ▁many ▁P rec amb rian ▁rocks ▁have ▁been ▁heavily ▁met am orph osed , ▁obsc uring ▁their ▁orig ins , ▁while ▁others ▁have ▁been ▁destroyed ▁by ▁er os ion , ▁or ▁remain ▁deeply ▁buried ▁beneath ▁Ph an ero zo ic ▁str ata . ▁ ▁It ▁is ▁thought ▁that ▁the ▁Earth ▁co ales ced ▁from ▁material ▁in ▁orbit ▁around ▁the ▁Sun ▁at ▁roughly ▁ 4 , 5 4 3 ▁Ma , ▁and ▁may ▁have ▁been ▁struck ▁by ▁a ▁very ▁large ▁( M ars - s ized ) ▁plan etes imal ▁shortly ▁after ▁it ▁formed , ▁splitting ▁off ▁material ▁that ▁formed ▁the ▁Moon ▁( see ▁Gi ant ▁impact ▁hypothesis ). ▁A ▁stable ▁cr ust ▁was ▁apparently ▁in ▁place ▁by ▁ 4 , 4 3 3 ▁Ma , ▁since ▁z ir con ▁cry st als ▁from ▁Western ▁Australia ▁have ▁been ▁dated ▁at ▁ 4 , 4 0 4 ▁ ± ▁ 8 ▁Ma . ▁ ▁The ▁term ▁" P rec amb rian " ▁is ▁recognized ▁by ▁the ▁International ▁Commission ▁on ▁Str at ig raph y ▁as ▁the ▁only ▁" sup ere on " ▁in ▁ge olog ic ▁time ; ▁it ▁is ▁so - called ▁because ▁it ▁includes ▁the ▁H ade an ▁( ~ 4 . 6 – 4 ▁billion ), ▁Ar che an ▁( 4 – 2 . 5 ▁billion ), ▁and ▁Pro ter oz o ic ▁( 2 . 5 ▁billion —