( They ( ( ( formed ( ( ( 250 million ) yr ) ago ) ) , ) ( when ( ( North ( American ( and ( African plates ) ) ) ) ( collided ( -LRB- ( ( ( before ( breakup ( of Pangaea ) ) ) . ) -RRB- ) ) ) ) ) ) )
(ROOT (S (NP (PRP They)) (VP (VBD formed) (ADVP (NP (QP (CD 250) (CD million)) (NN yr)) (RB ago)) (, ,) (SBAR (WHADVP (WRB when)) (S (NP (NNP North) (NNP American) (CC and) (NNP African) (NNS plates)) (VP (VBD collided) (PRN (-LRB- -LRB-) (PP (IN before) (NP (NP (NN breakup)) (PP (IN of) (NP (NNP Pangaea)))) (. .)) (-RRB- -RRB-))))))))
They formed 250 million yr ago, when North American and African plates collided (before breakup of Pangaea.)
(ROOT (S (NP (NNP Pangaea)) (VP (VBD began) (S (VP (VBG breaking) (ADVP (RB apart)) (ADVP (NP (QP (CD 250) (CD million)) (NNS years)) (RB ago))))) (. .)))