Europe South Asia Asia Pacific Americas Middle East Africa BBC Homepage World Service Education

Front Page



UK Politics







Talking Point

In Depth

On Air

Low Graphics

Wednesday, September 8, 1999 Published at 23:12 GMT 00:12 UK


Leaking Earth could run dry

Water flows into and out of the mantle

Japanese scientists say the Earth could be dry and barren within a billion years because the oceans are draining into the planet's interior.

Researchers from the Tokyo Institute of Technology have calculated that about 1.12 billion tonnes of water leaks into the Earth each year. Although a lot of water also moves in the other direction, not enough comes to the surface to balance what is lost.

Eventually, lead researcher Shigenori Maruyama and his colleagues believe, all of it will disappear.

[ image: Could Earth go the same way as Mars?]
Could Earth go the same way as Mars?
"Earth's surface will look very much like the surface of Mars, where a similar process seems to have taken place," Maruyama tells the latest edition of New Scientist magazine.

The water drains away at subduction zones, where the rock of the sea floor dives under the crustal rock that forms the continents. It is bound up in minerals in the transition zone, a layer of rock in the mantle that extends 400 to 650 kilometres below the surface of the Earth.

Geoscientists believe the water can return through volcanic hot spots and mid-ocean ridges, where molten rock from the upper mantle is pushed up through the Earth's crust. But the Tokyo calculations suggest only 0.23 billion tonnes makes it back each year - substantially less than is required to equalise the flows.

[ image: Water seeps into the Earth's interior at subduction zones]
Water seeps into the Earth's interior at subduction zones
Maruyama bases his calculations on estimates of the volumes of rock being moved up and down, together with experiments showing how much water is absorbed and released by the minerals and under what conditions.

His figures, which he describes as conservative, suggest the leakage has caused sea levels to drop by around 600 metres in the last 750 million years. This trend has been largely obscured in the geological record by shorter-term variations in sea levels.

Maruyama will present his findings at a meeting of the American Geophysical Union in San Francisco in December.

"The general idea appears quite plausible," says Raymond Jeanloz of the University of California at Berkeley. The difficulty, he says, is being sure you have accounted for all the mantle's inputs and outputs.

Advanced options | Search tips

Back to top | BBC News Home | BBC Homepage | ©

Sci/Tech Contents

Relevant Stories

08 Sep 99 | Sci/Tech
Deep-sea probe hunts new life-forms

08 Sep 99 | Sci/Tech
Seafloor observatories to monitor earthquakes

09 Feb 99 | Sci/Tech
Ocean vents were "factories of life"

08 Sep 99 | Sci/Tech
Deep heat under Hawaii

22 May 98 | Sci/Tech
Youngest land seen at sea

Internet Links

Ask An Earth Scientist

Volcano Watch

Internet Resources for Earth Science and Geology

New Scientist

Tokyo Institute of Technology

The BBC is not responsible for the content of external internet sites.

In this section

World's smallest transistor

Scientists join forces to study Arctic ozone

Mathematicians crack big puzzle

From Business
The growing threat of internet fraud

Who watches the pilots?

From Health
Cold 'cure' comes one step closer