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B. Scientists Propose a New Model of the Earth's Mantle

Narrator: This is Science Today. A proposed new model of the Earth's mantle may resolve a nearly 50-year old debate. Historically, seismologists have proposed the Earth's mantle circulates in one layer based on how far tectonic plates sink; but geochemists studying the composition of volcanic rocks had findings suggesting there was another, deeper layer. Louise Kellogg, a geologist at the University of California, Davis and her collaborators at MIT, merged previous observations into a single model and propose there are indeed two layers.

Kellogg:Basically we think there's this very hot layer which doesn't completely overturn.

Narrator: Kellogg says some have likened their model to a lava lamp.

Kellogg:A lava lamp has two compositions - it's got the clear stuff and it's got the waxy stuff. And the waxy stuff gets hot and starts to go up, but it doesn't mix with the clear stuff. Instead, it basically goes up a ways until it cools gets away from the lamp, then it drops back down again. And so we think something similar is happening in the deep mantle. That basically, there's a region of material, which is somewhat more intrinsically dense than the overlying mantle.

Narrator: For Science Today, I'm Larissa Branin.