Alexander Kendrick stands in the Lake of the Clouds after testing his invention. He and the team of cavers executed the deepest known digital communication ever to take place in the United States. Brad Horn for NPR hide caption

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The bdelloid rotifer Philodina gregaria. Bdelloid rotifers are tiny invertebrates that reproduce asexually. Courtesy of Micrographia hide caption

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Water in the atmosphere traps heat, like glass in a greenhouse. When there's less water vapor in the atmosphere, less heat is trapped. Space Frontiers/Getty Images hide caption

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A barefooted runner takes to the streets. Charlie Riedel/AP hide caption

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An artist's rendition of two Sinosauropteryx dinosaurs, showing their short, bristle-like feathers along the midline of the head, neck, back and around the tail, forming irregular stripes. Chuang Zhao and Lida Xing hide caption

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Workers ride past cooling towers at a coal-fired power plant on the outskirts of Beijing. Such power plants are at the center of a debate about the future of energy production in China and the U.S. Frederic J. Brown/AFP/Getty Images hide caption

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Tools like these ax heads from Vinelz, Switzerland, were used by Neolithic farmers and may have been part of their sex appeal to hunter-gatherer women. Sandstein via Wikimedia hide caption

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