A team of researchers has developed a measurement system that allows them to measure the thermal conductivity of Bridgman rocks in the laboratory under the pressure and temperature conditions that prevail in Earth’s interior. The research has been published in the journal Earth and Planetary Science Letters.

The evolution of our planet is the story of its cooling: 4.5 billion years ago, extreme temperatures prevailed on the surface of the young Earth, which was covered by a deep ocean of magma. Over millions of years, the Earth’s surface cooled to form a brittle crust. However, the enormous thermal energy emanating from the Earth’s interior triggers dynamic processes such as mantle convection, plate tectonics and volcanism. What remains unanswered, however, is how fast the Earth is cooling, and how long it will take for this continuous cooling to stop the aforementioned thermally driven processes.

One possible answer might lie in the thermal conductivity of the minerals that form the boundary between the core and mantle. This boundary layer is relevant because it is here that the sticky rock of the mantle comes into direct contact with the hot iron-nickel melt in the planet’s outer core. The temperature gradient between the two layers is very steep, so there can be a lot of heat flow here. The boundary layer is mainly formed by the mineral Brinell. However, it is difficult for researchers to estimate how much heat the mineral conducts from the core to the mantle because experimental verification is very difficult.

Now, ETH professor Motohiko Murakami from the Carnegie Institution for Science and his colleagues have developed a sophisticated measurement system that allows them to measure Bridgmanite’s concentration in the laboratory under the pressure and temperature conditions that are prevalent in Earth’s interior. Thermal conductivity. For the measurements, they used a recently developed optical absorption measurement system in a diamond cell heated with a pulsed laser.

“This measurement system allowed us to show that the thermal conductivity of Bridgmanite is about 1.5 times higher than assumed,” says ETH-Professor Motohiko Murakami. This suggests that the heat flow from the core to the mantle is also higher than previously thought. The greater heat flow, in turn, increases mantle convection and accelerates Earth’s cooling. This could cause plate tectonics (continuous convective motion through the mantle) to slow down faster than the researchers expected based on previous heat transfer values.

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