About twenty-nine percent or 133 million km2 of the earth's surface is made up of land. Contributing to about 2/3 of this area are forests, grasslands, and agriculture. Other categories of land include tundra's, marshes, deserts; scrub forests, urban areas, bare rock, and ice or snow. Deserts and other unproductive lands are important factors in biogeochemical cycles and biological diversity. Because of parks, wildlife refuges, and nature preserves nearly ten percent of the world's land surface is protected.
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