According to the geological theory of plate tectonics (which explains why the Earth’s crust makes large movements), the crust should be about 6.4 kilometers (4 miles) deep in this area, but is not. At the bottom of the hole is a layer of the Earth’s mantle.

The Earth’s mantle, about 70% of the total volume of the Earth, is a very dense, dark green colored rock that makes up the inner layer of the Earth. The mantle encases the Earth’s core, the iron-rich center of the Earth. It is generally about 2,900 kilometers (1,800 miles) thick. In sections that are thinner, the mantle has melted, leaving behind an outermost layer, or crust, of materials upon which humans live. The crust is less dense than the mantle and is composed mostly of basalt and granite.

To be able to take measurements of the Earth’s mantle is a scientific windfall for the exploratory team. They hope to be able to glimpse at some of the geological and chemical processes that are going on within the Earth’s interior.

Scientists suspect that the hole formed when either: (1) two tectonic plates pulled apart and, instead, of a usual melting mantle (of lava) coming up, it came up in solid form or (2) the crust was forced sideways, which left the hole.

This team of scientists will be making their exploration on the ship James Cook, a highly advanced British research ship. Besides the ship, they will also use a robotic submarine (called Toby) for measurements at the site. The main hole (others are also suspected to exist) is located about three miles below the Atlantic Ocean’s surface and about 2,000 nautical miles (3,700 kilometers) southwest of the Canary Islands.

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