7 March 2007

Deep ocean chasm baffles researchers

Associated Press
British scientists have embarked on an expedition to study a huge and enigmatic chasm in the Atlantic seafloor.
Deep ocean chasm baffles researchers

The expedition has set sail aboard the research vessel RRS James Cook Credit: National Environment Research Council

SANTA CRUZ DE TENERIFE, Spain: British scientists have embarked on an expedition to study a huge and enigmatic chasm in the Atlantic seafloor.

In an area covering many square kilometres of the mid-Atlantic ridge, the Earth’s crust is mysteriously missing. All that is there is a vast strech of bare mantle – dark green rock from deep inside the planet.

“This discovery is like an open wound on the surface of the Earth,” said Chris MacLeod, team member and marine geologist from Cardiff University in England. “Was the crust never there? Was it once there but then torn away on huge geological faults? If so, then how and why?”

The 12-member team, who will take an unprecedented peek in to the Earth’s mantle, left the Canary Islands on 5 March. They sailed aboard a new high-tech government-funded vessel equipped with 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 three kilometres below the surface of the Atlantic, about 2,000 nautical miles (roughly 3704 km) southwest of the Canaries mid-way between the Cape Verde Islands and the Caribbean.

It is part of a globe-spanning ridge of undersea volcanos, the kind of structure that forms when 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 six-kilometre-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.

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 also taking part in the six-week mission, said yesterday from the research ship RRS James Cook as it headed to the site, still five days away.

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.

There are two main theories as to what happened, Murton said: A fault ripped away huge chunks of crust, or in an area of crust-forming volcanoes, this area was mysteriously devoid of that outer material.

Roger Searle of Durham University, England, one of the lead researchers on the project, said that – as well as allowing scientists to peer into the Earth – the study aims to provide insights on everything from the chemistry of oceans to the mechanisms of how the Earth behaves under so much water.

The robotic device Toby will land on the exposed mantle, deploy a drill, and dig into the rock to bring back samples.

The project is being financed by the U.K.’s National Environment Research Council and the Department of trade and Industry’s Large Scientific Facilities Fund.

More information:

Progress of the expedition can be followed via a live webcam link here. The public are being encouraged to participate by emailing their questions to the crew.


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