( ( ( ( Extrusive or ) volcanic ) ( igneous rocks ) ) ( ( are ( ( formed ( by magma ) ) ( ( ( reaching ( ( the surface ) ( of ( the earth ) ) ) ) and ) solidifying ) ) ) . ) )
(ROOT (S (NP (ADJP (JJ Extrusive) (CC or) (JJ volcanic)) (NN igneous) (NNS rocks)) (VP (VBP are) (VP (VBN formed) (PP (IN by) (NP (NN magma))) (S (VP (VP (VBG reaching) (NP (NP (DT the) (NN surface)) (PP (IN of) (NP (DT the) (NN earth))))) (CC and) (VP (VBG solidifying)))))) (. .)))
Extrusive or volcanic igneous rocks are formed by magma reaching the surface of the earth and solidifying.
(ROOT (S (SBAR (WHADVP (WRB When)) (S (NP (NN magma)) (VP (VBZ reaches) (NP (DT the) (NN surface)) (PP (IN through) (NP (NP (NNS cracks)) (PP (IN in) (NP (NP (DT the) (NN earth) (POS 's)) (NN crust)))))))) (, ,) (NP (DT a) (JJ volcanic) (NN eruption)) (VP (VBZ occurs)) (. .)))