Oceans, and the innards of Earth itself, are the final frontiers of our planet. Expect amazing discoveries as explorers document more and more of this unseen realm. Hulton Archive/Getty Images hide caption

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We may not see them, but we need them. iStockphoto.com hide caption

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Ma Whero from Mischief of Comic Slams collides with Scarface Clawdia of Smash Malice during the Richter City Roller Derby Season Grand Final at TSB Arena on July 21, 2012 in Wellington, New Zealand. Hagen Hopkins/Getty Images hide caption

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Lyme disease is spread by deer ticks like this one. A study finds that some people can be reinfected many times with the bacteria that cause the disease. Lauree Feldman/Getty Creative Images hide caption

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Bacteroides species are some of the most common bacteria in the human gut. Enviornmental Health Perspectives hide caption

itoggle caption Enviornmental Health Perspectives