( ( in ( ( our atmosphere ) ( over ( the ( last ( 200 years ) ) ) ) ) ) . )
(ROOT (FRAG (PP (IN in) (NP (NP (PRP$ our) (NN atmosphere)) (PP (IN over) (NP (DT the) (JJ last) (CD 200) (NNS years))))) (. .)))
in our atmosphere over the last 200 years.
(ROOT (S (NP (NP (DT The) (NN composition)) (PP (IN of) (NP (DT the) (NN atmosphere)))) (VP (VBZ has) (VP (VBN changed) (PP (IN over) (NP (DT the) (JJ last) (CD 200) (NNS years))) (PP (RB primarily) (JJ due) (PP (TO to) (NP (JJ human) (NN activity)))))) (. .)))
The composition of the atmosphere has changed over the last 200 years primarily due to human activity.