March 6, 2007 — 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 three miles below the surface of the Atlantic and located 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 four-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.
Scientists have seen chunks of mantle that have been spewed up with lava, but never such a large, exposed stretch.
