▁of ▁millions ▁of ▁years , ▁occasionally ▁combining ▁to ▁make ▁a ▁super cont inent . ▁R ough ly ▁ 7 5 0   mill ion ▁years ▁ago , ▁the ▁earliest ▁known ▁super cont inent ▁Rod in ia , ▁began ▁to ▁break ▁apart . ▁The ▁contin ents ▁later ▁re comb ined ▁to ▁form ▁P annot ia ▁which ▁broke ▁apart ▁about ▁ 5 4 0   mill ion ▁years ▁ago , ▁then ▁finally ▁P ang ae a , ▁which ▁broke ▁apart ▁about ▁ 1 8 0   mill ion ▁years ▁ago . ▁ ▁During ▁the ▁Ne opro ter oz o ic ▁era , ▁free zing ▁temper atures ▁covered ▁much ▁of ▁the ▁Earth ▁in ▁gla ci ers ▁and ▁ice ▁sheets . ▁This ▁hypothesis ▁has ▁been ▁term ed ▁the ▁" S now ball ▁Earth ", ▁and ▁it ▁is ▁of ▁particular ▁interest ▁as ▁it ▁preced es ▁the ▁Camb rian ▁explos ion ▁in ▁which ▁mult ic ell ular ▁life ▁forms ▁began ▁to ▁pro l ifer ate ▁about ▁ 5 3 0 – 5 4 0   mill ion ▁years ▁ago . ▁ ▁Since ▁the ▁Camb rian ▁explos ion ▁there ▁have ▁been ▁five ▁distinct ly ▁ident ifiable ▁mass ▁ext in ctions . ▁The ▁last ▁mass ▁ext inction ▁occurred ▁some ▁ 6 6 ▁million ▁years ▁ago , ▁when ▁a ▁meteor ite ▁collision ▁probably ▁triggered ▁the ▁ext inction ▁of ▁the ▁non - av ian ▁din osa urs ▁and ▁other ▁large ▁re pt iles , ▁but ▁sp ared ▁small ▁animals ▁such ▁as ▁m amm als . ▁Over ▁the ▁past ▁ 6 6   mill