The earth's finite supply of 1,260 million, trillion liters of water has been in circulation through the hydrological cycle and the bodies of all living things for some 3.8 billion years. This water comes from a combination of that which was released from the earth's interior during its formative stages and that which landed here via icy asteroids. A fraction continues to rain down upon us from outer space. Only 2% of the world's water is potable, of which 1.6% is ice, 0.36% is subterranean, and a mere 0.036% exists (ephemerally) in lakes and rivers. Seawater covers 71% of the planet.
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Critical Ecosystem Partnership Fund, "The Biodiversity Hotspots," http://www.cepf.net/resources/hotspots/pages/default.aspx (accessed July 1, 2014). Data made available under the Creative Commons BY-SA 4.0 License: https://creativecommons.org/licenses/by-sa/4.0/legalcode.