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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 image suggests the Earth's appearance during 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, AKA refugia for the Earth's surviving soft-bodied multicellular organisms. In addition to the Marinoan glaciation there may have been at least two, and possibly three previous Proterozoic glacial periods going back to two billion years ago. The causes of these snowball periods are unknown but may have been due to massive volcanic eruptions, massive meteoritic impacts (both resulting in global sun-reflecting ash clouds), or variance's in the Earth's orbit.