Earth is softer in the middle than previously believed

January 25th, 2008 - 12:54 pm ICT by admin  

Washington, Jan 25 (ANI): A new study by scientists has suggested that the lower mantle of the Earth which is the middle section is softer than previously believed.

Conducted by scientists from the Carnegie Institutions Geophysical Laboratory, the new study came out with the theory after finding that material in part of the lower mantle has unusual electronic characteristics that make sound propagate more slowly.

This suggests that the material is softer than previously thought.

The lower mantle extends from about 400 miles to 1800 miles (660-2900 kilometers) into Earth and sits atop the outer core.

Pressures and temperatures are so brutal there that materials are changed into forms that dont exist in rocks at the planets surface and must be studied under carefully controlled conditions in the laboratory.

Iron is abundant in the Earth, and is a major component of the minerals ferropericlase and the silicate perovskite in the lower mantle. In previous work, researchers found that the outermost electrons of iron in ferropericlase are forced to pair up under the extreme pressures creating a so-called spin-transition zone within the lower mantle.

What happens when unpaired electronscalled a high-spin stateare forced to pair up is that they transition to what is called a low-spin state. And when that happens, the conductivity, density, and chemical properties change, explained Alexander Goncharov, the studys author.

According to Goncharov, the team determined the elasticity of ferropericlase through the pressure-induced high-spin to low-spin transition.

We did this by measuring the velocity of acoustic waves propagating in different directions in a single crystal of the material and found that over an extended pressure range (from about 395,000 to 590,000 atmospheres), the material became softerthat is, the (seismic) waves slowed down more than expected from previous work, he said.

Thus, at high temperature, corresponding distributions will become very broad, which will result in a wide range of depth having subtly anomalous properties that perhaps extend through most of the lower mantle. (ANI)

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