Scientists probe Earth’s deep mantle in the laboratory

Extreme conditions experiments sharpen view of our planet’s interior

Simulating the conditions 2700 kilometres deep underground, scientists have studied an important transformation of the most abundant mineral on Earth, bridgmanite. The results from the Extreme Conditions Beamline at DESY’s X-ray light source PETRA III reveal how bridgmanite turns into a structure known as post-perovskite, a transformation that affects the dynamics of Earth’s lower mantle, including the spreading of seismic waves. The analysis can provide an explanation for a range of peculiar seismic observations, as the team headed by Sébastien Merkel from the Université de Lille in France report in the Journal Nature Communications.
Bridgmanite is a magnesian-iron mineral ((Mg,Fe)SiO3) with a crystal structure that is not stable under ambient conditions. It forms about 660 kilometres below the surface of the Earth, and microcrystalline grains found as inclusions in meteorites are the only samples ever recovered on the surface. “In order to study bridgmanite under the conditions of the lower mantle, we had to produce the mineral first,” explains Merkel. To do so, the scientists compressed tiny amounts of iron-magnesium-silicon-oxide in a diamond anvil cell (DAC), a device that can squeeze samples with high pressure between two small diamond anvils.

Image: The crystal structures of bridgmanite (left) and post-perovskite (right).

Credit: Université de Lille, Sébastien Merkel
>Read more on the PETRA III (DESY) website