The boundary between Earth’s liquid iron core and solid silicate mantle — the D” layer at 2,900 km depth — remains one of the most enigmatic regions of our planet. Seismic studies reveal ultra-low velocity zones that cannot be explained by known mineral phases.

Extreme Conditions

Using laser-heated diamond anvil cells at BL-19, a team from Carnegie Institution reached pressures of 130 GPa and temperatures of 4,000K while collecting X-ray diffraction data with sub-second time resolution.

At these conditions, a new iron-bearing post-perovskite phase was observed with a density 3.2% higher than the previously known end-member. Simulations show this phase would produce exactly the seismic velocity reduction observed in ultra-low velocity zones.