January 25, 2008

Earth Gets Soft in the Middle

Earth’s middle layer may be squishier than previously thought.

A new study suggests the intense heat and pressure deep in the Earth makes sound waves travel more slowly through parts of the lower mantle than had been previously estimated, suggesting that part of this layer of the inner Earth is softer than expected.

Below the crust of the Earth (the layer we stand on) lies the viscous mantle. The lower portion of the mantle lies below the more rigid upper mantle and above the liquid outer core. It extends from about 400 to 1,800 miles (660 to 2,900 kilometers) below the surface.

Temperatures and pressures at this depth are so brutal that they can change the materials there into states that don't exist on Earth's surface. Pressures can reach 230,000 times the pressure at sea level and temperatures range from 2,800 to 6,700 degrees Fahrenheit (1,500 to 3,700 Celsius).

These forces change the configurations of electrons in the mineral ferropericlase in the lower mantle, making it "softer" than previously estimated.

The study, by Alexander Goncharov of the Carnegie Institution’s Geophysical Laboratory and colleagues, is detailed in the Jan. 25 issue of the journal Science.