Snowball Earth, artwork. This is how the Earth may have appeared about 650 million years ago during a period when snow and ice may have covered most, if not all, of the Earth's surface and oceans. This is the Marinoan glaciation from 650 to 630 million years ago. The southern and eastern hemispheres are dominated by glacier-covered land masses while the opposing hemisphere is frozen ocean save for a few areas of exposed liquid water. Such 'snowball' periods may be due to massive volcanic eruptions combined with a disturbed carbon cycle, massive meteoritic impacts, or variations in the Earth's orbit.