( ( Atmospheric pressure ) ( ( is ( ( the pressure ) ( ( caused ( by air ) ) ( when ( it ( ( exerts pressure ) ( on ( ( the surface ) ( of earth ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (JJ Atmospheric) (NN pressure)) (VP (VBZ is) (NP (NP (DT the) (NN pressure)) (VP (VBN caused) (PP (IN by) (NP (NN air))) (SBAR (WHADVP (WRB when)) (S (NP (PRP it)) (VP (VBZ exerts) (NP (NN pressure)) (PP (IN on) (NP (NP (DT the) (NN surface)) (PP (IN of) (NP (NN earth))))))))))) (. .)))
Atmospheric pressure is the pressure caused by air when it exerts pressure on the surface of earth.
(ROOT (S (PP (IN At) (NP (NP (DT the) (NN earth) (POS 's)) (NN surface))) (, ,) (NP (NP (DT the) (NN air) (NN pressure)) (VP (VBN exerted) (PP (IN on) (NP (PRP you))))) (VP (VBZ is) (NP (NP (DT a) (NN result)) (PP (IN of) (NP (NP (DT the) (NN weight)) (PP (IN of) (NP (NP (NN air)) (PP (IN above) (NP (PRP you))))))))) (. .)))