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C. Merging Two Ideas about the Inner Earth into One Theory

Narrator: This is Science Today. The Earth's mantle begins about twenty-two miles below our feet and travels on another 18 hundred miles. Since no one has ever drilled more than ten miles into the Earth, mantle analysts have to rely on indirect observations. Louise Kellogg, a geophysicist at the University of California, Davis, says different observations led to a difference of opinion among seismologists and geochemists. So Kellogg used both lines of thinking to come up with a new theory about the inner Earth.

Kellogg: We brought all the observations together into a single model in which, basically the very deep mantle has a somewhat different composition from the overlying mantle.

Narrator: Based on their findings, Kellogg suggests debate about the mantle may be due to seismologists tapping into one level of composition and geochemists into another.

Kellogg: And so now there's a lot of effort going into understanding the deep mantle. And so I think what people are going to do is try and focus some effort on regional studies of specific slabs and try and look for evidence for a layer and the deep mantle.

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