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Giant Slab of Earth’s Crust Found Near Core

A huge slab of folded Earth that scientists think used to be part of the ocean floor has been detected near the planet’s core. The discovery supports the theory that Earth’s crust is constantly recycled deep into the planet as molten material from below simultaneously pushes up to refresh the surface.

The structure is about 125 miles deep and at least 125 miles wide and 370 miles in the north-south direction. The slab began its plunge toward the center of the Earth about 50 million years ago. It is denser than surrounding material, which is why it sinks. Its lower reaches are near the core, about 1,740 miles down. Yet it is still attached to the surface, much like a conveyor belt.

Earth is divided into three main layers: the core, mantle and crust. The crust, a thin surface layer, is divided into more than a dozen major plates. In the middle of the Pacific Ocean, plates spread apart and fresh material from the mantle wells up.

Along the west coast of North America, crust beneath the ocean dives under a continental plate, creating earthquakes and volcanoes. Geologists have long speculated that when crust is folded into the planet, it sinks to the bottom of the mantle, where it displaces the material down there and forces some of it up.

If the scientists have correctly interpreted their data, the folding slab is the first hard evidence that sinking crust drives the upwelling of material so deep inside the planet.

The slab was found by monitoring seismic waves—generated by earthquakes in South America—reflecting from deep inside the mantle and recorded in the United States.

The diving crust is made of essentially the same material as the lower mantle, the researchers said, but it is much cooler, by about 1,260 degrees Fahrenheit. The lower mantle is roughly 4,500 degrees.

posted by: kyawoo at 21:32 | link | comments |
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