There is a 'thermal brake' deep inside the Earth that dictates how our planet cools down.
April 17, 2026
Original Paper
Iron spin crossover in ferropericlase and its effect on lower-mantle thermal conductivity
arXiv · 2604.14183
The Takeaway
Deep in the Earth's mantle, a mineral called ferropericlase is under crushing pressure. This study is the first to measure its heat-carrying ability at those extreme conditions, and they found that the iron inside it 'flips' its spin. This flip acts like a massive clog in a pipe, drastically reducing how fast heat can move from the core to the surface. It changes our entire timeline for how long the Earth will stay geologically active. Without this internal brake, the Earth might have frozen solid or stayed a molten mess much longer than it has.
From the abstract
Thermal conductivity of Earths lower mantle controls heat transfer across the core-mantle boundary (CMB) and strongly influences mantle convection. We report direct measurements of the thermal conductivity of single-crystal ferropericlase (Mg$_{1-x}$Fe$_x$O, $x = 0.09$-0.13), the second most abundant lower-mantle mineral, using optical laser flash and X-ray free-electron laser heating in diamond-anvil cells up to $\sim2200$~K and 130~GPa. These experiments provide the first conductivity data for