( ( An ( ice age ) ) ( ( is ( ( a period ) ( when ( ( for ( a ( long time ) ) ) ( ( ( the temperature ) ( of ( ( Earth 's ) climate ) ) ) ( is ( very low ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (DT An) (NN ice) (NN age)) (VP (VBZ is) (NP (NP (DT a) (NN period)) (SBAR (WHADVP (WRB when)) (S (PP (IN for) (NP (DT a) (JJ long) (NN time))) (NP (NP (DT the) (NN temperature)) (PP (IN of) (NP (NP (NNP Earth) (POS 's)) (NN climate)))) (VP (VBZ is) (ADJP (RB very) (JJ low))))))) (. .)))
An ice age is a period when for a long time the temperature of Earth's climate is very low.
(ROOT (S (NP (DT The) (NN climate)) (VP (VBZ is) (VP (VBN defined) (PP (IN as) (NP (NP (DT the) (NN temperature) (IN plus) (NN precipitation)) (PP (IN of) (NP (NP (DT an) (NN area)) (PP (IN over) (NP (NP (DT a) (JJ long) (NN period)) (PP (IN of) (NP (NN time))))))))))) (. .)))