Core formation

The core formed during accretion, as metal from impactors sank through a magma ocean to the center of the Earth. Liquid metal in contact with liquid silicate equilibrated at high pressures and temperatures, resulting in the core and mantle compositions that we see in the Earth today. If we understand how these reactions proceed as a function of pressure and temperature, we can compare this information to geochemical data on the composition of the Earth's mantle to learn about the conditions of core formation.

I combine iron-rich metal with mantle silicates and subject them to the pressures and temperatures of core formation using a laser-heated diamond anvil cell. After the experiment, I recover a cross-section of the sample using a Focused Ion Beam, then analyze it chemically using Transmission Electron Microscopy with collaborators in the ACCRETE project.

These data are then parameterized and combined with information about the Earth's mass evolution and provenance from N-body simulations to calculate the chemical evolution of the core and mantle during accretion and differentiation. This type of planetary-scale modeling gives us insight both into the core formation process and into the composition of the core today. My most recent work in this area involves using models of Earth's core formation to better understand the radiogenic Hf–W isotopic system, as well as modeling of core formation on Mars.

magma ocean
The Earth's magma ocean during core formation
A laser-heated diamond anvil cell

Related publications:
Brennan et al., submitted
Zube et al., 2019
Fischer and Nimmo, 2018
Fischer et al., 2017
Fischer et al., 2015

Press coverage:
Smithsonian YouTube channel