( They ( ( ( ( ( disappeared ( ( ( about 10,000 ) years ) ago ) ) , ) ( probably ( hunted ( to extinction ) ) ) ) ( by humans ) ) . ) )
(ROOT (S (NP (PRP They)) (VP (VP (VBD disappeared) (ADVP (NP (QP (RB about) (CD 10,000)) (NNS years)) (RB ago))) (, ,) (VP (ADVP (RB probably)) (VBN hunted) (PP (TO to) (NP (NN extinction)))) (PP (IN by) (NP (NNS humans)))) (. .)))
They disappeared about 10,000 years ago, probably hunted to extinction by humans.
(ROOT (S (NP (JJ Woolly) (NNS mammoths)) (VP (VBD began) (S (VP (TO to) (VP (VB go) (NP (NP (ADJP (JJ extinct)) (NNS thousands)) (PP (IN of) (NP (NNS years)))) (ADVP (RB ago) (PP (IN because) (PP (IN of) (S (VP (VBG hunting) (PP (IN by) (NP (NNS humans)))))))))))) (. .)))
Woolly mammoths began to go extinct thousands of years ago because of hunting by humans.