CANBERRA, Feb. 28 (Xinhua) -- Australian researchers have discovered than seawater cycles much further below the Earth's surface than first thought, reopening the age-old question about how oceans formed.
Researchers at the Australian National University (ANU) found that ocean water cycled up to 2,900 kilometers below the Earth's surface, well in excess of the previously-though 100 kilometers, throwing into doubt previous theories of how oceans and the atmosphere formed.
One theory previously thought to be true was that oceans formed when volcanic activity released gases and water from the Earth's mantle during the planet's first 100 million years.
But Dr Mark Kendrick from the ANU Research School of Earth Sciences on Tuesday said the new discovery throws that theory into doubt.
"Our findings make alternative theories for the origin of the atmosphere and oceans equally plausible, such as icy comets or meteorites bringing water to the Earth," Kendrick said in a statement on Tuesday.
He said seawater is introduced into the Earth's interior when two tectonic plates converge and one plate is pushed underneath the other into the mantle.
Previously it was thought seawater only made it around 100 kilometers under the Earth's mantle before it is returned to the surface, but the ANU study has "overturned" that notion.
Kendrick said the team analysed samples of volcanic glass from the Atlantic, Pacific and Indian oceans. They found traces of seawater in the galss, showing that ocean water had been deeply cycled throughout Earth's interior.
"The combination of water and halogens found in the volcanic glasses enables us to preclude local seawater contamination and conclusively prove the water in the samples was derived from the mantle," he said.