Enormous amounts of chemical elements move throughout the surface of the Earth. This illustrates how much is moved by various natural processes or human activities, in units of petagrams (Pg = 1015 grams), teragrams (Tg = 1012), and gigagrams (Gg =109). Enlarge for more details. (Reprinted with permission from Environmental Science & Technology © 2012, American Chemical Society)

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Enormous amounts of chemical elements move throughout the surface of the Earth. This illustrates how much is moved by various natural processes or human activities, in units of petagrams (Pg = 1015 grams), teragrams (Tg = 1012), and gigagrams (Gg =109). Enlarge for more details. (Reprinted with permission from Environmental Science & Technology © 2012, American Chemical Society)