by Ker Than
March 07, 2007
from FoxNews Website

A team of scientists will embark on a voyage next week to study an "open wound" on the Atlantic seafloor where the Earth's deep interior lies exposed without any crust covering.

The lesion is located mid-way between the Cape Verde Islands and the Caribbean in the Atlantic Ocean.

A map of the Earth showing relative crust thickness.

The red dot indicates the location of the rupture.

It lies nearly 2 miles beneath the ocean surface and extends over thousands of square kilometers.

"It's quite a substantial area," said Chris MacLeod, a marine geologist at Cardiff University in Wales, who will be part of the expedition.

Earth's tough skin

An outer crust of varying thicknesses covers most of the surface of the Earth like a shell. The crust is about 20 miles deep beneath continents and about 4 miles deep under the ocean floor.

The Earth's middle layer is called the mantle; it is heated by the Earth's core and is much hotter and softer than the crust.

Earth's crust is constantly being destroyed and created, and this cycle of destruction and renewal occurs faster with ocean crust than with continental crust.

New ocean floor crust forms at seams on the Earth's surface, called mid-oceanic ridges, where the planet's tectonic plates meet and where molten magma rises up from the planet's upper mantle.

The upwelling drives seafloor spreading, which is the movement of two oceanic plates away from each other. Oceanic crust is destroyed at so-called subduction zones where two plates collide and typically the denser one slips beneath another plate.

This is how scientists think it works, but areas of exposed mantle on the Earth's surface aren't easily explained by this theory.

They are regions,

"where this process seems to have gone wrong somehow," MacLeod said. "There's no crust formed, and instead we've got mantle - which is normally in the deep Earth - on the seafloor."

Really nail it down

Scientists have known about such anomalies for years, but it is only within the past decade that they have actively begun investigating them, MacLeod said.

In 2001, MacLeod was part of a team that visited the Atlantic Ocean gash.

"We ended up answering one or two questions but posing many more," he said. "What we're going to do with this expedition is try to really nail down what's happening."

There are two popular hypotheses about how these holes in the Earth's crust form.

"One is that the original volcanic crust did form, but that it's been ripped away by a huge rupture," MacLeod told LiveScience.

MacLeod likens this process to stretching a person's skin until it ruptures, exposing the flesh underneath.

"You take the crust and you stretch it and you pull it and pull it until it breaks," he said.

The other idea purports that somehow the area of exposed mantle was never covered by a magma crust in the first place.
 

A rare opportunity

Regardless of how they formed, the exposed mantle provides scientists with a rare opportunity to study the Earth's rocky innards.

Many attempts to drill deep into the planet barely get past the crust.

"One of our objectives now that we've got direct access to these mantle rocks is to try and look at their internal properties and try to find out about the deep Earth process that we can't get at directly," MacLeod said in a telephone interview.

Getting equipment down onto the seafloor where the exposed mantle is will be difficult, however.

"It's a very hazardous, very unforgiving environment," he said. "There are very steep slopes and huge pressures. So getting samples back from these areas is challenging still."

The team of researchers, led by Roger Searle of Durham University in England, will begin traveling to the site on March 5 aboard the new British research ship RSS James Cook.

Over the course of about six weeks, the team will use sonar to image the seafloor and a robotic seabed drill to collect rock cores.

Scientists Probe 'Hole in Earth'
1 March 2007

from BBCNews Website

A drill will be used to extract samples of the exposed mantle
 

Scientists are to sail to the mid-Atlantic to examine a massive "open wound" on the Earth's surface.

Dr Chris MacLeod, from Cardiff University, said the Earth's crust appeared to be missing across an area of several thousand square kilometers. The hole in the crust is midway between the Cape Verde Islands and the Caribbean, on the Mid-Atlantic Ridge.

The team will survey the area, up to 5km (3 miles) under the surface, from ocean research vessel RRS James Cook. The ship is on its inaugural voyage after being named in February. Dr MacLeod said the hole in the Earth's crust was not unique, but was recognized as one of the most significant.

He said it was an "open wound on the surface of the Earth", where the oceanic crust, usually 6-7km thick (3.7-4.3 miles), was simply not there.

"Usually the plates are pulled apart and to fill the gap the mantle underneath has to rise up. As it comes up it starts to melt. That forms the magma," he said.

"That's the normal process. Here it has gone awry for some reason."

"The crust does not seem to be repairing itself."

Dr MacLeod said the research could lead to a "new way of understanding" the process of plate tectonics.

The scientist will test theories he developed after visiting the area in 2001 - including the possibility the missing crust was caused by a "detachment fracture".

"Effectively it's a huge rupture - one side is being pulled away from the other. It's created a rupture so big it's actually pulled the entire crust away.

 

 

A rock called serpentinite is exposed at the surface
 

 

"We also think the mantle did not melt as much as usual and that the normal amount of mantle was not produced."

As a result, the mantle is exposed to seawater, creating a rock called serpentinite.

The survey voyage, costing $1m (£510,000), will be led by marine geophysicist Professor Roger Searle, from Durham University. Dr Bramley Murton, from the National Oceanography Centre, Southampton, is the third expert taking part.

They will set sail from Tenerife on Monday and return in April.

The team intends to use sonar to build up an image of the seafloor and then take rock cores using a robotic seabed drill developed by the British Geological Survey in conjunction with Dr MacLeod.

The progress of the voyage can be followed online.