A worker stands on top of a storage bin on July 27, 2011, at a drilling operation in Claysville, Pa. The dust is from powder mixed with water for hydraulic fracturing. Keith Srakocic/AP hide caption

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Space tourist Dennis Tito celebrates after his landing near the Kazakh town of Arkalyk on May 6, 2001. Alexander Nemenov/AFP/Getty Images hide caption

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Health officials around the world are on constant lookout for the deadly bird flu. Here a worker collects chickens on a farm in Kathamndu, Nepal, where the virus was suspected of infecting poultry last October. Prakas Mathema/AFP/Getty Images hide caption

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A worker makes a cut in the side of a sandstone block at the Cleveland Quarries facility in Vermilion, Ohio, earlier this month. The legal limit on the amount of silica that workers can inhale was set decades ago. Ty Wright/Bloomberg via Getty Images hide caption

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Health workers in Nepal culled chickens and destroyed eggs following an outbreak of bird flu in Kathmandu in October 2012. Prakash Mathema/AFP/Getty Images hide caption

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Two chimps groom each other at the Save the Chimps facility in Florida. The National Institutes of Health owns about 360 chimpanzees that aren't yet retired and that are living at research facilities; new guidelines say most of its chimps should be retired. Save the Chimps hide caption

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Researchers at the U.S. Geological Survey National Wildlife Health Center in Madison, Wis., use eggs to see if the Asian strain of the H5N1 bird flu virus has entered the U.S. in this photo from 2006. Andy Manis/AP hide caption

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A health official culls chickens on a poultry farm in a village on the outskirts of Katmandu, Nepal. Chickens suspected of being infected with H5N1 bird flu were found in the area in October. Prakash Mathema/AFP/Getty Images hide caption

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A prefectural officer carries a chicken on a poultry farm on Oct. 15 on the outskirts of Kathmandu, Nepal, where chickens suspected of being infected with bird flu were found. Prakash Mathema /AFP/Getty Images hide caption

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The Mariner 2 probe at an assembly facility in Cape Canaveral, Fla., on Aug. 29, 1962. NASA/JPL/Caltech hide caption

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Cmdr. Eugene Cernan tests the lunar vehicle on the surface of the moon during the Apollo 17 mission. NASA hide caption

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Can You Tell Emotion From Faces Alone? A new study suggests that when people evaluated just facial expressions — without cues from the rest of the body — they couldn't tell if the face was showing a positive or negative emotion. Enlarge this photo to see the answers. Hillel Aviezer/The Hebrew University of Jerusalem hide caption

itoggle caption Hillel Aviezer/The Hebrew University of Jerusalem