
The deep mantle, a region that lies 416 to 1,800 miles (670 to 2,900 kilometers) below the Earth's surface, is impossible to reach and hard to "see" clearly with seismic signals. The little scientists do know about the mantle comes from earthquake waves, which speed up and slow down as they travel through different rock layers inside the Earth. The deepest part of the mantle has weird blobs and seismic slow zones that have long puzzled scientists. Both new studies offer possible explanations for the strange seismic behavior.
In the studies, researchers mimicked conditions inside the deep mantle with experiments in the laboratory. Teams working independently on different continents shot lasers at tiny specks of rock squeezed between diamond anvils.
One team concluded that scientists had been wrong about the form that a certain rock takes in the deep mantle, which accounts for about half of Earth's volume. The other team found evidence for small amounts of Earth's most common surface rock, basalt, pooling in liquid form at the core-mantle boundary. The findings are published today (May 22) in the journal Science.
"These results are a new step forward in reproducing in the laboratory what is occurring in the very deep mantle," said Denis Andrault, lead author of one of the studies and a scientist at Blaise Pascal University in France.











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