( ( As ( ( live coral ) ( grows ( atop ( ( the skeletons ) ( on ( dead coral ) ) ) ) ) ) ) ( , ( ( a ( coral reef ) ) ( ( is formed ) . ) ) ) )
(ROOT (S (SBAR (IN As) (S (NP (JJ live) (NN coral)) (VP (VBZ grows) (PP (IN atop) (NP (NP (DT the) (NNS skeletons)) (PP (IN on) (NP (JJ dead) (NN coral)))))))) (, ,) (NP (DT a) (NN coral) (NN reef)) (VP (VBZ is) (VP (VBN formed))) (. .)))
As live coral grows atop the skeletons on dead coral, a coral reef is formed.
(ROOT (S (NP (NNS Corals)) (VP (VBP build) (NP (NP (JJ hard) (NNS exoskeletons)) (SBAR (WHNP (WDT that)) (S (VP (VBP grow) (S (VP (TO to) (VP (VB become) (NP (NN coral) (NNS reefs)))))))))) (. .)))