Earth gets one of its nicknames, the Blue Planet, from the way it looks from space. About 70 percent of the planet's surface is covered with water, a substance that known types of life can't do without. All told, the oceans, land, and atmosphere hold the equivalent of almost 1.4 billion cubic kilometers of liquid water. About 96.5 percent of that total is salty ocean, a little more than 2 percent of the
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