Don't Panic: Earth's Nine Threats to Humanity

By Eric Roston - 2011-12-13T01:58:47Z

Photograph by George Steinmetz/National Geographic Stock

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When it comes to moving Earth around, geological forces just can't compete with agriculture, construction and mining.

Since the last ice age, natural sediment flows amounted to about 21 gigatons a year. Compare that with 75 gigatons a year of lost cropland soil from modern farming, according to a 2007 study in the Geological Society of America Bulletin. Deforestation and water stress often accompany the expansion of agriculture in new areas, straining natural systems.

Agriculture now covers about 12 percent of ice-free land, according to the boundaries study. In Dunhuang, China, sand dunes loom over farms, advancing at a rate of six feet each year.

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