OddTodd

North America was once home to mammoths, mastodons (above) and beavers the size of black bears. Barry Roal Carlsen/University of Wisconsin-Madison hide caption

toggle caption Barry Roal Carlsen/University of Wisconsin-Madison

A close-up composite image of a dust particle. The green patches contain bromine, calcium and/or iron. Courtesy of American Chemical Society hide caption

toggle caption Courtesy of American Chemical Society

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