Earth's oceans were homegrown and not delivered by icy comets and asteroids as long contended, U.S. researchers say.
Astronomers have long theorized that comets and asteroids delivered the water for the world's oceans during an epoch of heavy bombardment that ended about 3.9 billion years ago, but researchers at Massachusetts Institute of Technology contend the water came from the very rocks that formed the planet, AAAS ScienceMag.org reported Monday.
Geologist Linda Elkins-Tanton says computer simulations show a large percentage of the water in the molten rock forming the early Earth would quickly form a steam atmosphere before cooling and condensing into an ocean.
The process would take only tens of millions of years, suggesting oceans were flowing over the Earth by as early as 4.4 billion years ago, she says.
Even the scant amount of water in the mantle would have produced oceans hundreds of meters deep, she reports in an article to be published in the journal Astrophysics and Space Science.
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