How Did Water Get on Earth?
Each time you take a sip of water, you’re imbibing liquid that, in all likelihood, is up to 4.5 billion years old. Earth is awash in a life-sustaining substance about as ancient as the planet itself. Astrophysicists don’t completely know where the stuff came from, but circumstantial evidence suggests that water-containing meteorites might have pummeled an infant Earth. Those rocky showers would have helped transform a bone-dry place into a unique wet world. When the solar system first came together, some of the young planets were too hot for water. “Earth and Mars should have formed extremely dry,” says Humberto Campins, an asteroid expert at the University of Central Florida—due to their locations in the solar system’s frost line. "The pieces of the puzzle are not clear," says Campins, who is a member of the team that probed Bennu's contents. But he points to one major clue that "gives us an idea of where the water may be coming from": the type of hydrogen that flows through our aquatic systems.
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