( ( ( The proposal ) ( that ( ( ( ( ( ( Mars , ) ( early ( in ( its history ) ) ) ) , ) ( had ( ( some complement ) ( of water ) ) ) ) and ) ( ( ( an atmosphere ) ( of ( carbon ( ( dioxide and ) nitrogen ) ) ) ) ( ( much ( more dense ) ) ( than today ) ) ) ) ) ) ( ( ( is not ) unreasonable ) . ) )
(ROOT (S (NP (NP (DT The) (NN proposal)) (SBAR (IN that) (S (S (NP (NP (NNP Mars)) (, ,) (NP (NP (JJ early)) (PP (IN in) (NP (PRP$ its) (NN history)))) (, ,)) (VP (VBD had) (NP (NP (DT some) (NN complement)) (PP (IN of) (NP (NN water)))))) (CC and) (S (NP (NP (DT an) (NN atmosphere)) (PP (IN of) (NP (NN carbon) (NN dioxide) (CC and) (NN nitrogen)))) (ADJP (ADJP (RB much) (RBR more) (JJ dense)) (PP (IN than) (NP (NN today)))))))) (VP (VBZ is) (RB not) (ADJP (JJ unreasonable))) (. .)))
The proposal that Mars, early in its history, had some complement of water and an atmosphere of carbon dioxide and nitrogen much more dense than today is not unreasonable.
(ROOT (S (PP (IN During) (NP (DT the) (JJ early) (NN paleozoic))) (, ,) (NP (NP (DT the) (NN amount)) (PP (IN of) (NP (NP (NN carbon) (NN dioxide)) (PP (IN in) (NP (DT the) (NN atmosphere)))))) (VP (VBD was) (ADJP (RB much) (JJR greater)) (PP (VBN compared) (PP (TO to) (NP (NN today))))) (. .)))