THE idea that Earth was entirely frozen over about 700 million years ago - the so-called Snowball Earth hypothesis - poses one small problem: how did our planet thaw out? The conundrum could be explained if the Earth was more mudball than snowball.
Evidence for Snowball Earth comes from the discovery of glacial rock formations around the world that date back to this time. One proposed explanation for the subsequent thawing is that carbon dioxide levels soared during the freeze, warming the planet. But recent studies of oxygen isotopes suggest that the level of CO2 was only a tenth of that required to melt the ice.
Now Dorian Abbot and Raymond Pierrehumbert of the University of Chicago have used climate models to study how dust from volcanoes and the weathering of rocks would affect the thaw. They found that in regions where the amount of snowfall was low and any snow that did settle was sublimating away, enough dust would have accumulated to change the surface albedo sufficiently so that the Earth absorbed sunlight and thawed (Journal of Geophysical Research – Atmospheres, DOI: 10.1029/2009jd012007, in press).
"It could get you out of the snowball at an appropriate CO2 value," says Abbot. The mudball hypothesis is testable, he adds, by searching for a "dust signal" in rock formations of the appropriate age.
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This actually makes a lot of sense. Considering a super volcano the size of yellow stone would cover approximately 5% of the earth's surface in ash, that would certainly cause enough warming to begin the thawing as long as the eruption took place after all cooling effects had stalled
While not as likely as volcanic dust to produce the volume required meteor dust accumulated over a long period of time with low precipitation would reduce the albedo too. Perhaps the recent article on dark matter creating the Gould Belt could be linked - if you can push enough matter to make stars you should be able to knock a few things out of orbit to make a nice prolonged meteor shower.
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