( ( During ( this period ) ) ( ( ( ( ( ( marine animals ) ( with ( mineralized shells ) ) ) ( made ( their ( first appearance ) ) ) ) and ) ( ( Cambrian rocks ) ( are ( the ( first ( to ( contain ( ( an abundance ) ( of fossils ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (PP (IN During) (NP (DT this) (NN period))) (S (NP (NP (JJ marine) (NNS animals)) (PP (IN with) (NP (JJ mineralized) (NNS shells)))) (VP (VBD made) (NP (PRP$ their) (JJ first) (NN appearance)))) (CC and) (S (NP (NNP Cambrian) (NNS rocks)) (VP (VBP are) (NP (DT the) (JJ first) (S (VP (TO to) (VP (VB contain) (NP (NP (DT an) (NN abundance)) (PP (IN of) (NP (NNS fossils)))))))))) (. .)))
During this period marine animals with mineralized shells made their first appearance and Cambrian rocks are the first to contain an abundance of fossils.
(ROOT (S (NP (NP (DT The) (NN presence)) (PP (IN of) (NP (NP (DT an) (NN animal) (NN fossil)) (PP (IN in) (NP (DT a) (NN rock)))))) (VP (VBZ gives) (NP (NP (NN evidence)) (PP (IN of) (NP (DT the) (NN time) (NN period)))) (NP (NP (DT the) (NN animal)) (VP (VBN lived) (PP (IN in))))) (. .)))
The presence of an animal fossil in a rock gives evidence of the time period the animal lived in.