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NATURE

Leaky seas drying up Earth, scientists report

mars
Water flows into the mantle through trenches and leaves through middle ocean ridges and volcanic hot spots.  

September 17, 1999
Web posted at: 3:07 p.m. EDT (1907 GMT)

ENN



Geoscientist predict the Earth will be as dry and barren as Mars in a billion years, due to leaky seas. Within a billion years, the Earth could dry up and resemble Mars barren and waterless, according to geologists from the Tokyo Institute of Technology. Their calculations show the oceans are leaking billions of gallons of water into the Earth and only a trickle is coming back out, according to a report the Sept. 11 issue of New Scientist.

Geoscientists believe that huge amounts of water are trapped in minerals deep in the transition zone between the Earth's upper and lower mantles, located about 250 miles below the planet's surface. Water gets into the mantle at subduction zones where oceanic crust plates plunge underneath continental plates. Some water resurfaces at volcanic hot spots and middle ocean ridges, where hot molten rock from the upper mantle is pushed up through the Earth's crust.

Until now, most researchers assumed that these flows were roughly in balance. But Shigenori Maruyama and his colleagues at the Tokyo Institute of Technology tried to provide some real numbers on the rate of the disappearing water and they came to a different conclusion. They believe the oceans are leaking water five times as fast as it is being replenished.

"The general idea appears quite plausible," Raymond Jeanloz of the University of California at Berkeley told New Scientist.

The Tokyo geoscientists said about 1.2 billion tons of ocean water seeps into the mantle's transition zone. Yet, they only figured 0.23 billion tons move out of the mantle. "The world's oceans will dry up within a billion years," Maruyama told New Scientist. "Earth's surface will look very much like the surface of Mars, where a similar process seems to have taken place."

"In the early part of Earth's history, the temperature gradient in the subduction zones was far too high. But around 750 million years ago the subduction zones cooled to the point where the process could begin," Maruyama told New Scientist. Since then, Maruyama estimates the leakage caused sea levels to drop nearly 2,000 feet.

Maruyama believes his figures are conservative, but admits uncertainties in the exact amount of water coming back out of the Earth. He will present his findings at a December meeting of the American Geophysical Union in San Francisco.

Even if Maruyama's calculations are correct, the process will not reverse the current sea level rise caused by global warming, according to the report. Leaky oceans will seem a small problem in comparison to the Sun which will have expanded so much that it will be making life uncomfortably hot for anything left on the planet, according to New Scientist.

Copyright 1999, Environmental News Network, All Rights Reserved



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