Scientist: There is little doubt that the ice ages were caused by the unusually rich growth of vegetation worldwide  Since vegetation converts carbon dioxide into oxygen, excessive vegetation would have depleted the carbon dioxide in the atmosphere  Carbon dioxide helps the atmosphere retain the sun' s heat
Thus, if this carbon dioxide is depleted, the earth cools significantly, thereby causing an ice age
If the carbon dioxide in the atmosphere is depleted, the earth cools significantly, thereby causing an ice age.