If you think the greenhouse gas emissions that may raise atmospheric temperatures as much as 11 degrees by the end of this century are an unprecedented global event, think again. About 55 million years ago, according to scientists, there was a massive global warming event that raised temperatures about 10 degrees, and the culprit then -- as now -- was greenhouse gases. Where'd they come from? Turns out that the same intense volcanic activity that sundered Greenland from the Americas and created Iceland also cooked so much of the Earth's crust that it released gases previously trapped in decaying, carbon-rich organic sediments. Volcanic vents on the sea floor were to blame as well; they liberated so much methane trapped in icy material on the seabed that for many thousands of years, the land and sea of the North Atlantic region experienced a major "outgassing," turning the entire landscape into a kind of Hellish, organic smokestack. As bad as that sounds, however, consider this: back then it took about 100,000 years for the atmospheric temperature to rise ten degrees; we, on the other hand, are much more efficient in that regard. For the full story, click here.

Image courtesy USGS.