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Deep in the Atlantic, a stretch of Earth's mantle lies exposed

By ASSOCIATED PRESS
Published March 7, 2007

SANTA CRUZ DE TENERIFE, Canary Islands - British scientists have embarked on a mission to study a huge area on the Atlantic seabed where the Earth's crust is mysteriously missing and instead is covered with dark green rock from deep inside the planet.

The 12-member expedition to take an unprecedented peek at Earth's mantle left the Canary Islands on Monday with a new high-tech vessel and a robotic device named Toby that will dig up rock samples at the site and film what it sees.

The main site - there is at least one other in roughly the same area and a third is suspected - is about 3 miles below the surface of the Atlantic Ocean, about 2,000 nautical miles southwest of the Canaries.

It is part of a globe-spanning ridge of undersea volcanos, the kind of structure that forms when Atlantic tectonic plates separate and lava surges upward to fill the gap in the Earth's crust.

But that apparently did not happen this time. Where there should be a 4-mile-thick layer of crust, there is instead that much mantle, the very dense, dark green rock that makes up the deep inner layer of the Earth.

This exposed layer is irregularly shaped, about 30 miles long and perhaps that distance or more at its widest. It was detected about five years ago with sonar from a surface vessel.

Scientists have seen chunks of mantle that have been spewed up with lava, but never such a large, exposed stretch.

"It is like a window into the interior of the Earth," Bramley Murton, a geophysicist who is taking part in the six-week mission, said Tuesday from the research ship RRS James Cook as it headed to the site, still five days away.

The project is being financed by Britain's National Environment Research Council and the Department of Trade and Industry's Large Scientific Facilities Fund.

[Last modified March 7, 2007, 01:21:49]