( ( ( ( Professor ( Robert ( van ( der Hilst ) ) ) ) and ) ( his collaborators ) ) ( ( ( ( ( demonstrated conclusively ) ( that ( ( convection ( in ( ( the ( Earth 's ) ) mantle ) ) ) ( involves ( ( tectonic plates ) ( ( ( sinking ( from ( ( Earth 's ) surface ) ) ) deep ) ( into ( the ( lower mantle ) ) ) ) ) ) ) ) ) and ) ( later ( ( found ( evidence ( for ( compositional stratification ) ) ) ) ( at ( ( larger depth ) ( than ( hitherto thought ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NP (NNP Professor) (NNP Robert) (NNP van) (NNP der) (NNP Hilst)) (CC and) (NP (PRP$ his) (NNS collaborators))) (VP (VP (VBD demonstrated) (ADVP (RB conclusively)) (SBAR (IN that) (S (NP (NP (NN convection)) (PP (IN in) (NP (NP (DT the) (NN Earth) (POS 's)) (NN mantle)))) (VP (VBZ involves) (NP (NP (JJ tectonic) (NNS plates)) (VP (VBG sinking) (PP (IN from) (NP (NP (NNP Earth) (POS 's)) (NN surface))) (ADVP (RB deep)) (PP (IN into) (NP (DT the) (JJR lower) (NN mantle))))))))) (CC and) (VP (ADVP (RB later)) (VBD found) (NP (NP (NN evidence)) (PP (IN for) (NP (JJ compositional) (NN stratification)))) (PP (IN at) (NP (NP (JJR larger) (NN depth)) (PP (IN than) (NP (NN hitherto) (NN thought))))))) (. .)))
Professor Robert van der Hilst and his collaborators demonstrated conclusively that convection in the Earth's mantle involves tectonic plates sinking from Earth's surface deep into the lower mantle and later found evidence for compositional stratification at larger depth than hitherto thought.
(ROOT (S (NP (NNS Rises)) (ADVP (RB then)) (VP (ADVP (RB sinks)) (VBZ does) (NP (NP (JJR deeper) (NN material) (NN cause) (NN convection)) (PP (IN in) (NP (DT the) (NN mantle))))) (. .)))