Snowball Earth

The Evidence

The scientists that champion the "Snowball Earth" theory have accumulated many lines of evidence to support their work. The first line of evidence comes from a climate model created by Mikhail Budyko of the Leningrad Geophysical Observatory in the 1960's. Budyko's calculations showed that the ice-albedo feedback (albedo is a measure of how much solar radiation is reflected back into space) created an instability in the climate. He showed that if ice formed in lower latitudes then planetary albedo would rise at a faster rate. Once ice formed beyond 30 degrees north or south latitude (the critical limit) created a positive feedback plummeting the temperatures and freezing the planet.

At first few people paid little interest in the theory since if the Earth had ever been frozen as Budyko suggested, it should still be frozen today since there was no model for breaking the freeze. Secondly, it was assumed that a frozen planet would have exterminated all life. The second assumption was found to be false in the 1970's with the discovery of communities of organisms that live in extreme environments such as deep-sea hydrothermal vents and in the cold mountain valleys of Antarctica. The first assumption was broken by plate tectonics. The new theory of plate tectonics was beginning to take hold among geologists in the 1970's and the movement of the Earth's crust and the volcanism that results from it, was the key needed to breaking the freeze.

In the 1980's, Joe Kirschvink began to examine the problem of a global glaciation. Because of plate tectonics, he deduced, the levels of CO2 in the atmosphere would continue to increase because of plate tectonics. If the Earth was frozen and there was no liquid water on the continents, then the effects of weathering would cease and would allow CO2 to build up to very high levels. Over time the warming generated by the CO2 greenhouse gas would offset the effect of the ice-albedo and the freeze would be broken. Kirschvink, along with colleagues from Pennsylvania State University, calculated that about 0.12 bar of CO2 (350 times present day concentrations) would be needed to overcome the albedo of the "Snowball Earth". Using current rates of CO2 emissions from volcanoes, Kirschvink figured that it would require millions to tens of millions of years for the sea ice at the equator to melt, making the "Snowball Earth" not only the coldest, but the

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