▁turn ▁alter ▁or ▁transform . ▁From ▁the ▁broad est ▁ge oph ys i ological ▁point ▁of ▁view , ▁the ▁b ios phere ▁is ▁the ▁global ▁e colog ical ▁system ▁integr ating ▁all ▁living ▁be ings ▁and ▁their ▁relationships , ▁including ▁their ▁interaction ▁with ▁the ▁elements ▁of ▁the ▁l ith os phere ▁( ro cks ), ▁hyd ros phere ▁( water ), ▁and ▁atmosphere ▁( air ). ▁The ▁entire ▁Earth ▁contains ▁over ▁ 7 5   b ill ion ▁tons ▁( 1 5 0 ▁tr ill ion ▁pounds ▁or ▁about ▁ 6 . 8 × 1 0 1 3   kil og rams ) ▁of ▁bi om ass ▁( life ), ▁which ▁lives ▁within ▁various ▁environments ▁within ▁the ▁b ios phere . ▁ ▁Over ▁nine - t enth s ▁of ▁the ▁total ▁bi om ass ▁on ▁Earth ▁is ▁plant ▁life , ▁on ▁which ▁animal ▁life ▁depends ▁very ▁heavily ▁for ▁its ▁existence . ▁More ▁than ▁ 2 ▁million ▁species ▁of ▁plant ▁and ▁animal ▁life ▁have ▁been ▁identified ▁to ▁date , ▁and ▁estimates ▁of ▁the ▁actual ▁number ▁of ▁existing ▁species ▁range ▁from ▁several ▁million ▁to ▁well ▁over ▁ 5 0   mill ion . ▁The ▁number ▁of ▁individual ▁species ▁of ▁life ▁is ▁constantly ▁in ▁some ▁degree ▁of ▁flux , ▁with ▁new ▁species ▁appearing ▁and ▁others ▁ce asing ▁to ▁exist ▁on ▁a ▁contin ual ▁basis . ▁The ▁total ▁number ▁of ▁species ▁is ▁in ▁rapid ▁decl ine . ▁ ▁E volution ▁ ▁The ▁origin ▁of ▁life ▁on ▁Earth ▁is ▁not ▁well ▁understood , ▁but ▁it ▁is ▁known ▁to