http://www.pbs.org/wgbh/nova/earth/cause-ice-age.html http://www.pbs.org/wgbh/nova/earth/cause-ice-age.html http://www.pbs.org/wgbh/nova/earth/cause-ice-age.html NOVA ^ ice age Ice Ages ice age http://www.pbs.org/wgbh/nova/earth/cause-ice-age.html http://www.pbs.org/wgbh/nova/earth/cause-ice-age.html http://www.pbs.org/wgbh/nova/earth/cause-ice-age.html causing an ice age ice age Nova Online / Cracking the Ice Age http://www.pbs.org/wgbh/nova/earth/cause-ice-age.html 50 million years this http://www.pbs.org/wgbh/nova/earth/cause-ice-age.html http://www.pbs.org/wgbh/nova/earth/cause-ice-age.html most recent period of glaciation NOVA ^ Ice Age Causes