Rebecca Fischer

Rebecca FischerRebecca Fischer
Clare Boothe Luce Assistant Professor of Earth and Planetary Sciences
Department of Earth and Planetary Sciences
Faculty of Arts and Sciences

I am the Clare Boothe Luce Assistant Professor in the Department of Earth and Planetary Sciences at Harvard. I am moving to Harvard from a postdoctoral position jointly at the Smithsonian National Museum of Natural History and the University of California Santa Cruz; prior to that, I obtained my Ph.D. in Geophysical Sciences from the University of Chicago in 2015, and my B.A. in Earth and Planetary Sciences and Integrated Science from Northwestern University in 2009. 
Some awards that I am most proud of include both a Graduate Research Fellowship and Postdoctoral Fellowship from the National Science Foundation, a Graduate Research Fellowship from the Illinois Space Grant Consortium, a Ludo Frevel Crystallography Scholarship from the International Centre for Diffraction Data, an American Dissertation Fellowship from the American Associate of University Women, and a Graduate Research Award from the American Geophysical Union.
My research addresses three fundamental stages of Earth and planetary evolution: the modern-day core composition, the core formation process, and accretion. To investigate these processes, I use a combination of high pressure, high temperature experiments and numerical modeling. The experiments use a diamond anvil cell, in which microscopic samples are compressed between two diamonds in a hand-held press to achieve pressures of the Earth’s core. At these pressures, we use infrared lasers to locally heat the samples to thousands of Kelvin, allowing us to study its properties in situ or ex situ.
Understanding the composition of Earth’s core, in particular the identity and abundance of core material that is less dense than iron, is important to our knowledge of the core formation process and chemical history of the planet's interior; dynamics of the outer core and magnetic field generation; inner core structure and properties; and thermal structure of the Earth. I study phase diagrams and equations of state of Fe-rich alloys, then compare their densities and other properties to seismologically-determine properties of the core to constrain its composition.
I also study the chemical reactions between molten metal and silicate (core and mantle analogues) at high pressures and temperature that occurred during core formation. These reactions can tell us about the current core composition and the conditions of core formation. After subjecting the metal and silicate to very high pressures and temperatures, the materials are analyzed by electron microscopy. Combining data on these reactions with information about how the Earth accreted, I then model the chemical evolution of the Earth as it formed and differentiated.
Since the core was forming while the Earth was still growing, we need to understand how pressure, temperature, and composition of the Earth evolved during accretion. I ran a large suite of simulations of terrestrial planet accretion to study this process. The simulations provide information about the mass evolution of the Earth and the provenance of its building blocks, which I then use to model core–mantle chemical evolution. I have also been using these models to trace the isotopic provenance of Earth, Theia, Mars, and other planets.

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