ETH Zurich professor Motohiko Murakami and researchers at the Carnegie Institution for Science have developed a sophisticated measurement system that allows them to measure the thermal conductivity of bridgmanite , which only exists in the interior of our planet at depths unreachable for us (except in the science fiction), but in a laboratory setting.
Although we know that surface and atmospheric temperatures fluctuate over eons, the planet’s interior has been cooling since Earth formed about 4.5 billion years ago.
A story of gradual cooling
The immense thermal energy emanating from the Earth’s core set in motion several dynamic processes, such as plate tectonics, volcanism, and mantle convection. The question is that scientists do not agree on how fast the Earth has gradually cooled or how much time is left for all these dynamic processes related to heat to stop due to this drop in temperature.
Thus, to try to shed light on this aspect, because verifying it experimentally is very complicated, scientists have used a recently developed optical absorption measurement system in a diamond unit heated with a pulsed laser in order to measure the thermal conductivity of the bridgmanite, under the pressure and temperature conditions that prevail inside the Earth, but in the laboratory.
At some point in our planet’s future history, the core will solidify and geological activity will cease, likely turning Earth into barren rock , due to the lack of our vast magnetic field that protects us and allows life prosper.
When will this happen?
According to the current work, sooner than we thought. The researchers irradiated a single crystal of bridgmanite with pulsed lasers. The result? It simultaneously increased its temperature to 2440 Kelvin and pressure to 80 gigapascals, close to what we know to be conditions in the lower mantle – up to 2630 Kelvin and 127 gigapascals of pressure.
“This measurement system allows us to show that the thermal conductivity of bridgmanite is about 1.5 times higher than previously assumed. This suggests that the heat flux from the core to the mantle is also greater than previously thought. Increased heat flux, in turn, increases mantle convection and accelerates Earth’s cooling. This may cause plate tectonics, which is kept going by convective motions of the mantle, to slow faster than researchers expected based on previous heat conduction values, ” explains Motohiko Murakami in his published paper. in the journal Earth and Planetary Science Letters.
The researchers are not able to specify -for now- how long it will take for the convection currents to stop, but what it does give us is a new perspective on the evolution of the Earth’s dynamics.
Referencia: Motohiko Murakami, Alexander F. Goncharov, Nobuyoshi Miyajima, Daisuke Yamazaki, Nicholas Holtgrewe. Radiative thermal conductivity of single-crystal bridgmanite at the core-mantle boundary with implications for thermal evolution of the Earth. Earth and Planetary Science Letters, 2022; 578: 117329 DOI: 10.1016/j.epsl.2021.117329
