▁where : ▁▁ ▁t ▁is ▁the ▁age ▁of ▁the ▁sample , ▁▁ λ ▁is ▁the ▁decay ▁constant ▁of ▁ 1 8 7 Re , ▁ ▁( e λ t - 1 ) ▁is ▁the ▁slope ▁of ▁the ▁is och ron ▁which ▁defines ▁the ▁age ▁of ▁the ▁system . ▁ ▁A ▁good ▁example ▁of ▁an ▁application ▁of ▁the ▁Re - Os ▁is och ron ▁method ▁is ▁a ▁study ▁on ▁the ▁d ating ▁of ▁a ▁gold ▁depos it ▁in ▁the ▁Wit w aters rand ▁min ing ▁camp , ▁South ▁Africa . ▁ ▁R hen ium - os m ium ▁is ot op ic ▁evolution ▁ ▁R hen ium ▁and ▁os m ium ▁were ▁strongly ▁ref ract ory ▁and ▁s ider oph ile ▁during ▁the ▁initial ▁acc ret ion ▁of ▁the ▁Earth ▁which ▁caused ▁both ▁elements ▁to ▁prefer entially ▁enter ▁the ▁Earth ' s ▁core . ▁Thus ▁the ▁two ▁elements ▁should ▁be ▁de ple ted ▁in ▁the ▁sil icate ▁Earth ▁yet ▁the ▁ 1 8 7 Os ▁/ ▁ 1 8 8 Os ▁ratio ▁of ▁mant le ▁is ▁ch ond rit ic . ▁The ▁reason ▁for ▁this ▁apparent ▁contradiction ▁is ▁ow ed ▁to ▁the ▁change ▁in ▁behavior ▁between ▁Re ▁and ▁Os ▁in ▁partial ▁m elt ▁events . ▁Re ▁tends ▁to ▁enter ▁the ▁m elt ▁phase ▁( in compatible ) ▁while ▁Os ▁remains ▁in ▁the ▁solid ▁resid ue ▁( compatible ). ▁This ▁causes ▁high ▁r ati os ▁of ▁Re / Os ▁in ▁ocean ic ▁cr ust ▁( which ▁is ▁derived ▁from ▁partial ▁mel ting ▁of ▁mant le