( ( ( The circulation ) ( of ( ( mantle rock ) ( as ( it ( ( ( ( ( ( ( rises ( to ( ( the top ) ( of ( the asthenosphere ) ) ) ) ) , ) cools ) , ) and ) then ) sinks ) ) ) ) ) ) ( ( is ( known ( as ( a ( convection current ) ) ) ) ) . ) )
(ROOT (S (NP (NP (DT The) (NN circulation)) (PP (IN of) (NP (NP (JJ mantle) (NN rock)) (SBAR (IN as) (S (NP (PRP it)) (VP (VP (VBZ rises) (PP (TO to) (NP (NP (DT the) (NN top)) (PP (IN of) (NP (DT the) (NN asthenosphere)))))) (, ,) (VP (VBZ cools)) (, ,) (CC and) (ADVP (RB then)) (VP (VBZ sinks)))))))) (VP (VBZ is) (VP (VBN known) (PP (IN as) (NP (DT a) (NN convection) (NN current))))) (. .)))
The circulation of mantle rock as it rises to the top of the asthenosphere, cools, and then sinks is known as a convection current.
(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))))) (. .)))