( ( ( ( ( ( ( The ( Earth 's ) ) atmosphere ) ( is ( 78 ( percent ( nitrogen gas ) ) ) ) ) , ) but ) ( ( ( plants and ) animals ) ( ( can not ) ( ( ( use nitrogen ) ( directly ( from ( the air ) ) ) ) ( as ( they ( do ( carbon ( ( dioxide and ) oxygen ) ) ) ) ) ) ) ) ) . )
(ROOT (S (S (NP (NP (DT The) (NN Earth) (POS 's)) (NN atmosphere)) (VP (VBZ is) (NP (CD 78) (NN percent) (NN nitrogen) (NN gas)))) (, ,) (CC but) (S (NP (NNS plants) (CC and) (NNS animals)) (VP (MD can) (RB not) (VP (VB use) (NP (NN nitrogen)) (PP (ADVP (RB directly)) (IN from) (NP (DT the) (NN air))) (SBAR (IN as) (S (NP (PRP they)) (VP (VBP do) (NP (NN carbon) (NN dioxide) (CC and) (NN oxygen)))))))) (. .)))
The Earth's atmosphere is 78 percent nitrogen gas, but plants and animals cannot use nitrogen directly from the air as they do carbon dioxide and oxygen.
(ROOT (S (NP (NN Nitrogen) (NN gas)) (VP (VBZ comprises) (NP (NP (QP (RB about) (NNS three-fourths))) (PP (IN of) (NP (NP (NN earth) (POS 's)) (NN atmosphere))))) (. .)))