A farmer harvests corn on a farm near Spring Mills, Pa. According to current biofuel laws, if you burn ethanol from corn in your car, the government doesn't count the carbon dioxide that comes out of the tailpipe as an actual carbon emission. Carolyn Kaster/AP hide caption

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Gunnar Oquist (left), permanent secretary of the Royal Swedish Academy of Sciences, and Ingemar Lindstrom of the Academy sit next to portraits of the 2009 Nobel Physics Prize winners in Stockholm on Tuesday. Scanpix Sweden/Bertil Ericson/AP hide caption

itoggle caption Scanpix Sweden/Bertil Ericson/AP

President Obama waves from the doorway of Air Force One on Monday as he prepares to fly to New York for the U.N. General Assembly. Hans Pennink/AP hide caption

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A glacier in Patagonia, Argentina, calves, with a sudden collapse of ice. Researchers say that the activity that precedes these types of tipping points and the triggers that cause them may follow predictable patterns. Philip Stanley Dickson/iStockphoto.com hide caption

itoggle caption Philip Stanley Dickson/iStockphoto.com

A more than 30,000-year-old dyed flax fiber found in Georgia. It's likely that early humans used plants in the area to color the fibers. Eliso Kvavadze hide caption

itoggle caption Eliso Kvavadze

In the study, cotton-top tamarins grew calmer after they heard music compositions based on their own calm, friendly calls, and became more agitated when exposed to music that contained elements of their own threatening or fearful calls. Bryce Richter/University of Wisconsin-Madison hide caption

itoggle caption Bryce Richter/University of Wisconsin-Madison