Pebblesbysea

The Snowball theory by Paul F Hoffman and Daniel P Schrag

A potential explanation for the rare occurrence of “snowball” events in Earth history is an unusual continental configuration. Paleomagnetic evidence suggests that there were few if any continents at high latitudes 600-700 million years ago. When most continents are close to the Equator, the Earth is deprived of a mechanism that keeps the amount of carbon dioxide in the atmosphere above a critical level.

If carbon dioxide in the atmosphere were to slowly drop over millions of years due to a slow reduction in volcanic activity, global temperatures would drop and glaciers would cover the high-latitude continents, just as ice sheets cover Antarctica and Greenland today. The ice sheets prevent chemical weathering, the process that converts carbon dioxide to carbonate, from proceedin. This stabilizes the levels of carbon dioxide in the atmosphere.

But if all the continents were in the tropics, such a “safety switch” would not work, as the continents would remain ice-free even as the Earth grew colder, approaching the critical threshold for a snowball. Such a theory is speculative, although some unusual behavior of the carbon cycle is implicated by the unusually high amount of carbon-13 in sediments of Neoproterozoic time.

We may never know the true cause, as we have but simple theories for the ultimate forcing of climate change even in recent times. But clearly a successful answer must explain both why a glacial runaway happens and why it is such a rare event.

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