Cleaning behavior of blue-striped grunt and four-eyed butterfly fish, Florida Keys National Marine Sanctuary -- Stephen Frink/Corbis

Cleaning behavior of blue-striped grunt and four-eyed butterfly fish, Florida Keys National Marine Sanctuary -- Stephen Frink/Corbis

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The pearl monument in the Corniche neighborhood of Doha, Qatar, illuminated at night with the new high-rises of West Bay in the background -- Jon Hicks/Corbis

The pearl monument in the Corniche neighborhood of Doha, Qatar, illuminated at night with the new high-rises of West Bay in the background -- Jon Hicks/Corbis

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Dead trees in Dead Vlei, Namib-Naukluft Park, Namibia -- Frank Krahmer/Corbis

Dead trees in Dead Vlei, Namib-Naukluft Park, Namibia -- Frank Krahmer/Corbis

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Saddleback caterpillar on a leaf in the Cockscomb Basin, Belize -- Frans Lanting/Corbis

Saddleback caterpillar on a leaf in the Cockscomb Basin, Belize -- Frans Lanting/Corbis

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Roof of the Stephansdom (St. Stephen’s) Cathedral, Vienna, Austria -- Walter Bibikow/Corbis

Roof of the Stephansdom (St. Stephen’s) Cathedral, Vienna, Austria -- Walter Bibikow/Corbis

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Staghorn coral, Great Barrier Reef, off the coast of Australia -- Frans Lanting/Corbis

Staghorn coral, Great Barrier Reef, off the coast of Australia -- Frans Lanting/Corbis

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