A team of geologists and mineral physicists at Harvard University, the University of California, Argonne National Laboratory and the University of Chicago has found evidence via lab experiments that show the Earth’s mantle is far more complex than previously known.

In their study, published in the journal Nature Communications, the group used a multi-anvil press and a machine-learning approach to chart how ringwoodite (a high-pressure phase of magnesium silicate) properties in the mantle can vary at different depths.

Prior research has suggested that the interesting parts of Earth are on the surface, where plate tectonics and weather erosion cause a lot of changes, and in the core, where churning molten iron generates the planet’s magnetic field. The mantle, by contrast, was seen as little more than a thick layer of hot rock, with the occasional plume pushing its way through. Now, the team on this new effort reports that a lot more is going on in the mantle than previously thought.

Recent research by several teams has shown that that mantle has a layer that no one knew about—and its flow patterns are much more complex than would be expected in that part of the planet. Such findings have come courtesy of new tools that allow geophysicists to track shifting speeds of waves generated by earthquakes as they move through the mantle, allowing scientists to create a sort of CT scan of the inside of the Earth.

Just 10 years ago, researchers found that some plumes could make their way from the base of the mantle all the way to the surface, while others stalled before they make it that far.

Researchers have also found that seismic waves change speeds nearly uniformly at depths of 660 kilometers, suggesting the material there is either harder or softer than the material around it, further suggesting a previously unknown layer of material. The depth appeared to coincide with a form of olivine called ringwoodite as it breaks down. Also, a team last year found evidence of another layer 1,050 kilometers down.

For this new study, the researchers conducted lab experiments designed to imitate phase transitions in the mantle layers. They found that the material at the depths where the new layers are thought to exist can have transitions that vary under both pressure and temperature, which explains why the boundaries appear to change. They suggest that such changes in the mantle might explain why some plumes stagnate while others make their way to the crust.

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