( ( In ( ( the ( Earth 's ) ) atmosphere ) ) ( , ( nitrogen ( ( acts ( as ( a ( buffer gas ) ) ) ) . ) ) ) )
(ROOT (S (PP (IN In) (NP (NP (DT the) (NN Earth) (POS 's)) (NN atmosphere))) (, ,) (NP (NN nitrogen)) (VP (VBZ acts) (PP (IN as) (NP (DT a) (NN buffer) (NN gas)))) (. .)))
In the Earth's atmosphere, nitrogen acts as a buffer gas.
(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))))) (. .)))