A piece of the earth is missing?

OK, it's a huge chunk of the earth's crust.

LONDON (Reuters) - A team of British scientists has set sail on a voyage to examine why a huge chunk of the earth's crust is missing, deep under the Atlantic Ocean -- a phenomenon that challenges conventional ideas about how the earth works.

The 20-strong team aims to survey an area some 3,000 to 4,000 metres deep where the mantle -- the deep interior of the earth normally covered by a crust kilometres thick -- is exposed on the sea floor.

Experts describe the hole along the mid-Atlantic ridge as an "open wound" on the ocean floor that has puzzled scientists for the five or so years that its existence has been known because it defies existing tectonic plate theories of evolution.

There is a lot more information at the project's web site.

Mid-ocean ridges are a fascinating component of our planet's armour plating. Mid-ocean ridges are the place where new oceanic crust is born, with red-hot lava spewing out along the spreading axis as seafloor spreading progresses. However, the mechanisms by which this occurs are still not well understood by scientists - hardly suprising when you consider that mid-ocean ridges are located thousands of metres below the surface of the ocean.

Scientists have discovered a large area thousands of square kilometres in extent in the middle of the Atlantic Ocean where the Earth's crust seems to be missing entirely. Instead, the mantle - the deep interior of the Earth, normally covered by crust many kilometres thick - is exposed on the seafloor, 3000m below the surface. It has been described as being like an open wound on the surface of the Earth. What scientists don't know is whether the ocean crust was first developed, and then ripped away by huge geological faults, or whether it never even developed in the first place.

In March-April 2007, a team of scientists from Durham University, Cardiff University and NOCS will board the RRS James Cook to visit this special area of the Mid-Atlantic Ridge, which is called the Fifteen-Twenty Fracture Zone (FTFZ for short - the map on the left shows where this is located).

Until about 130 million years ago South America and Africa were part of the super continent Gondwana. It doesn't take a lot of imagination to see that the east side of South America and the west side of Africa fit together like a jigsaw puzzle. The mid Atlantic ridge shown on the map is where the two broke apart. The study area is in that break away zone.