This March 24 aerial photo shows the extent of damage at the Fukushima Dai-ichi nuclear power plant in Japan. The 40-foot-tall tsunami destroyed the electrical and cooling systems, resulting in meltdowns at some of the reactors. Air Photo Service/AP hide caption

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The snowpack in the Rocky Mountains has been gradually thinning over the past century. Using tree ring measurements from subalpine larch trees like these in the Lake Chelan Wilderness in Washington state, researchers were able to put the Rocky Mountain data in long-term historical context. Jeremy S. Littell/UW Climate Impacts Group hide caption

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Shoppers crowd a narrow street outside Tsukiji market in Tokyo on Dec. 31, 2010. Japan has relatively tight social rules. And that makes sense, according to researchers. When people are squeezed together, they have an incentive to cooperate. Toru Yamanaka/AFP/Getty Images hide caption

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A worker checks the status of the water level at the Unit 1 reactor at the Fukushima Dai-ichi nuclear power plant in Japan on Tuesday. Japanese officials said the reactor doesn't appear to be holding water, which means its core probably sustained more damage than originally thought. TEPCO/AP hide caption

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Two cells — one marked mostly in green, the other in blue — of a newly discovered organism found in water samples collected from the University of Exeter pond. Scientists think these "cryptomycota" use their tails to propel themselves while searching for food. Meredith Jones/Nature hide caption

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A Chinese farmer sweeps up dried cobs and stripped corn on a roadside outside Beijing. A new study finds that global production of corn and wheat would have been 5 percent higher if not for global warming. Alexander F. Yuan/AP hide caption

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Alligator River National Wildlife Refuge is a low-lying area made of 154,000 acres of marshland and forest on the eastern shore of North Carolina. Much of the land is susceptible to sea level rise, so conservation managers are taking steps to help slow the inevitable. U.S. Fish and Wildlife Service hide caption

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Workers at the Fukushima Dai-ichi nuclear power plant spray a substance to help reduce dust on April 1. The cleanup operation at the facility could take more than a decade. TEPCO hide caption

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Nighthawks are known for their repeated "peent" call as they hunt for flying insects. Bill Bouton/Flickr hide caption

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