( ( ( ( ( It ( ( is conceivable ) ( that ( ( ( ( ( in ( ( the absence ) ( of ( atmospheric oxygen ) ) ) ) , ) and ) ( given ( enough time ) ) ) ( , ( ( other metabolisms ) ( could ( be dominant ) ) ) ) ) ) ) ) , ) but ) ( ( ( ( any plant ) , ) ( that ( is ( ( any ( photosynthetic organism ) ) ( that ( does ( ( develop ( aerobic metabolism ) ) ( on ( such ( a world ) ) ) ) ) ) ) ) ) ) ( will ( outcompete ( its neighbors ) ) ) ) ) . )
(ROOT (S (S (NP (PRP It)) (VP (VBZ is) (ADJP (JJ conceivable)) (SBAR (IN that) (S (PP (PP (IN in) (NP (NP (DT the) (NN absence)) (PP (IN of) (NP (JJ atmospheric) (NN oxygen))))) (, ,) (CC and) (PP (VBN given) (NP (JJ enough) (NN time)))) (, ,) (NP (JJ other) (NNS metabolisms)) (VP (MD could) (VP (VB be) (ADJP (JJ dominant)))))))) (, ,) (CC but) (S (NP (NP (DT any) (NN plant)) (, ,) (SBAR (WHNP (WDT that)) (S (VP (VBZ is) (NP (NP (DT any) (JJ photosynthetic) (NN organism)) (SBAR (WHNP (WDT that)) (S (VP (VBZ does) (VP (VB develop) (NP (JJ aerobic) (NN metabolism)) (PP (IN on) (NP (PDT such) (DT a) (NN world)))))))))))) (VP (MD will) (VP (VB outcompete) (NP (PRP$ its) (NNS neighbors))))) (. .)))
It is conceivable that in the absence of atmospheric oxygen, and given enough time, other metabolisms could be dominant, but any plant, that is any photosynthetic organism that does develop aerobic metabolism on such a world will outcompete its neighbors.
(ROOT (S (PP (IN On) (NP (DT a) (JJ global) (NN scale))) (, ,) (NP (NP (NNS plants)) (CC and) (NP (JJ other) (JJ photosynthetic) (NNS organisms))) (VP (VBP have) (VP (VBN generated) (NP (NP (DT all)) (PP (IN of) (NP (NP (DT the) (NN oxygen)) (PP (IN in) (NP (DT the) (NN air)))))))) (. .)))
On a global scale, plants and other photosynthetic organisms have generated all of the oxygen in the air.