Earth’s Interior Could Be Cooling Faster Than We Thought

The extremely hot interior of the Earth is slowly cooling, but the exact rate remains unknown. By studying the ability of a common deep-Earth mineral to conduct heat, researchers from Carnegie and ETH Zurich have discovered that the planet’s interior may be cooling much faster than we thought. .

The Earth is essentially a giant pie that has been cooling on a windowsill for 4.5 billion years. At first it was hot from the surface to the center, covered with oceans of magma, but as it cooled from the outside in, a solid crust of rock was formed. The core is still radiating huge amounts of heat into the mantle, driving vital processes like plate tectonics and volcanism, but it will also eventually cool.

Exactly how long it will take is a mystery, but scientists in the new study sought answers by investigating a key mineral called bridgmanite. The boundary layer between the outer core and the lower mantle is composed mostly of bridgmanite, so studying the mineral’s ability to conduct heat could have major implications for the planet. The problem is that the collection of these measurements is difficult to perform in the laboratory.

So the researchers placed samples of bridgmanite in a diamond anvil cell that was heated using a laser system to simulate the intense pressures and temperatures deep within the Earth. Then, they measured the thermal conductivity of the bridgmanite using an optical absorption system.

The team found that bridgmanite conducts heat about 1.5 times better than long thought. This, in turn, would mean that heat passes more easily from the core to the mantle, accelerating the rate at which the inner Earth cools.

And it could go even faster over time. As bridgmanite cools, it turns into another mineral called post-perovskite, which is an even more efficient conductor of heat. When this new mineral begins to dominate the boundary, the Earth’s interior could cool even faster.

“Our results could give us a new perspective on the evolution of Earth’s dynamics,” said Motohiko Murakami, corresponding author of the study. “They suggest that Earth, like the other rocky planets Mercury and Mars, is cooling and becoming inactive much faster than expected.”

While the researchers aren’t sure exactly how long this process might take, it’s important to note that this acceleration occurs on geologic timescales. Earth’s interior may be cooling faster than previously thought, but it will still happen over billions of years.

The research was published in the journal Earth and Planetary Science Letters.

Source: ETH Zürich

Betty K. Park