Earth's mantle has a gooey layer we never knew about [View all]

By Stephanie Pappas published 3 days ago
While the mantle is mostly solid, a layer about 93 miles (150 kilometers) down is melty, new research finds.



A schematic of Earth's hot inner layers. New research finds that the uppermost layer of the crust is partially melted. (Image credit: Shutterstock)

Most of Earth's mantle is hot but solid, with rocks that deform slowly rather than cracking like the cooler rocks of the crust do. But new research finds that around 93 miles (150 kilometers) below Earth's surface, there is a worldwide layer of melted rock.

Discovering this gooey layer will help researchers better understand how the tectonic plates "float" on top of this mantle layer, study first author Junlin Hua, a postdoctoral researcher in geosciences at the University of Texas at Austin, told Live Science.

The melted rock is in the asthenosphere, the upper layer of the mantle that sits between about 50 miles (80 km) and 124 miles (200 km) below Earth's surface. The only way to peer into this layer of the mantle is with seismic waves from earthquakes. Researchers can detect the waves at seismic stations set up around the world, looking for subtle changes in the waveforms that indicate what kinds of materials the waves traveled through. Previously, researchers knew from these types of studies that some parts of the asthenosphere were hotter than others, Hua said, and patchy areas of melt had been detected. But little was known about how deep and widespread the melt was.

Oddly, though, this melted layer doesn't seem to affect the movements of the tectonic plates. The researchers found that the areas of melt did not affect the mantle's viscosity, or tendency to flow.

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