The term Snowball Earth usually means the periods of ice formation, global in extent, occurred during Precambrian time. The Sturtian Glaciation ended about 700 million years ago, the Marinoan Glaciation about 635 million years ago, and the Gaskiers Glaciation about 580 million years ago. There was an earlier period of ice formation, about 2.4 billion years ago, about which much less is known, because there are far fewer deposits that have survived from that distant time. The ice formed on both land and sea, not only in polar and temperate latitudes but even in the tropics, which would have made the Earth look very much like a snowball. Because there may have been little open ocean, there would have been very little evaporation, hence very little rain or snow, once the snowball conditions formed.

Calculations by Russian scientist Mikhail Budyko in the 1960s suggested that the Earth could never have had such a period of cold temperatures, because if this had occurred, the Earth would have remained frozen forever. This would occur because of the albedo effect: The sunlight would have reflected from the white snow and ice, directly back into outer space, without being absorbed; the only sunlight that creates warmth is the sunlight that is absorbed. (This is why a stick lying on top of the snow on a sunny day will melt its way into the snow; the stick absorbs sunlight and becomes warm, while the snow does not.) Budyko's calculations did not include the effects of volcanic eruptions. Eruptions would have created numerous unfrozen spots in the ocean and would have released carbon dioxide into the atmosphere. Carbon dioxide contributes to the greenhouse effect by absorbing infrared photons that are emitted by the Earth. Very little infrared light would have been emitted by a Snowball Earth, but as carbon dioxide levels built up over millions of years, enough heat might have accumulated to begin melting the ice. Two major processes by which carbon dioxide is removed from the air are the photosynthesis of organisms and the weathering of rocks. With so few organisms, and with the rocks and oceans covered by ice, there would have been almost nothing to remove carbon dioxide from the air, thus allowing it to accumulate. These processes would have allowed the Earth to emerge from its snowball condition.

Snowball Earth is an example of a truly radical theory that has become widely accepted, in various forms, by the scientific community. Its principal proponents are geologists Paul Hoffman and Daniel Schrag of Harvard University, basing their studies on earlier work by geologists Joseph Kirschvink and Brian Harland. . .

Free term papers are not written to satisfy your specific instructions. You can use our professional writing services to buy a custom written research paper, term paper, or essay on Science at affordable price. CustomTermPapers is the best solution for those who seek help in writing term papers, essays, and research papers related to Science and other relevant topics.