The previously unknown temperature gradient in Earth's largest layer is uniquely extracted from a seismology average, the only information available. Data used from laboratory studies are minimal and describe general behavior. Adding a new theory and data on heat transport properties provides flux (heat per area per time) and power (total wattage) vs. depth. Temperature vs. depth instead uses an additive constant, which is constrained by data on melting. I show the lower mantle is heating up.

We investigated the thermal vibrations of ⁵⁷Fe atoms in the crystal structure of a high-pressure form of the oxyhydroxide compound (Al,Fe)OOH. The results of our nuclear resonant inelastic X-ray scattering experiments on single crystals show that ⁵⁷Fe atoms vibrate at different frequencies and with different amplitudes when being displaced in different directions. This anisotropy of atomic vibrations is transmitted to related thermal properties and can be described using second-rank tensors.