( Stratigraphy ( ( is ( ( based ( on ( ( the deposition ) ( of ( ( distinctive strata ) ( of ( rock layers ) ) ) ) ) ) ) ( over time ) ) ) . ) )
(ROOT (S (NP (NNP Stratigraphy)) (VP (VBZ is) (VP (VBN based) (PP (IN on) (NP (NP (DT the) (NN deposition)) (PP (IN of) (NP (NP (JJ distinctive) (NN strata)) (PP (IN of) (NP (NN rock) (NNS layers))))))) (PP (IN over) (NP (NN time))))) (. .)))
Stratigraphy is based on the deposition of distinctive strata of rock layers over time.
(ROOT (S (NP (PRP We)) (VP (VBP call) (NP (NP (DT the) (NN study)) (PP (IN of) (NP (NN rock) (NNS layers)))) (ADVP (RB stratigraphy))) (. .)))