Experimental Investigations of Carbon in Earth's Core

Regents Of The University Of Michigan - Ann Arbor, Ann Arbor MI

Investigators

Abstract

Experimental Investigations of Carbon in Earth?s Core Intellectual merit. Previous studies proposed that the global carbon cycle involved Fe3C or Fe7C3 as a dominant component in the solid portion of Earth?s core, even though critical data to test the hypothesis of carbide-rich inner core are still missing. Experimental results on the phase relation of the Fe-C binary system are limited to 70 GPa. Sound velocity data are only available for Fe3C, under conditions up to 68 GPa at 300 K and up to 47 GPa at high temperatures. Density measurements on Fe3C have reached ~ 200 GPa in pressure, but high temperature data are scarce. In particular, experiments are needed to assess the effects of magnetic transition near 70 GPa on the thermoelastic and vibrational properties of the iron carbides, and to quantify the influence of temperature on their magnetism, density and sound velocities. It is proposed to investigate the compression and melting behavior of iron carbides up to the core pressure regime and ~ 3000 K using multi-anvil and diamond anvil cell pressure devices. Specific goals include: [1] determine the partial phonon density of Fe3C and Fe7C3 using the nuclear resonant scattering method; [2] establish the thermal equation of state of Fe3C and Fe7C3 using the synchrotron X-ray diffraction methods; [3] determine the eutectic composition of the Fe-C binary system using a combination of in situ X-ray diffraction and focused ion beam FIB-based quench analysis methods. The proposed activities will provide new data on the phase relations, densities, and sound velocities of candidate iron carbides to core pressures and high temperatures, thus enabling a stringent test of inner core models involving carbon as a major component. The expected results will advance our understanding of Earth?s deep carbon cycle, a central and timely issue in solid Earth research. The investigations will establish stepping-stones toward an ultimate model of core chemistry by elucidating the role of magneto-volume and anharmonicity in the thermodynamics and lattice vibration of potential core materials. Key constraints on the carbon content of the core will complement geochemical, seismological, and geodynamic studies to expand the frontier of deep Earth research. This work will also contribute to astrophysics and planetary science on the pathways of carbon from star birth to planet differentiation, and to materials science and condensed-matter physics on the behavior of carbon-based materials and strongly correlated systems under extreme environments. Broader impact. The lead PI is committed to teaching and training at high school to postdoctoral levels through course offerings, lectures, and tutorial sessions (e.g., for the Michigan Math and Science Scholar program and at the Cooperative Institute for Dynamic Earth Research Summer Schools). The proposed experiments will train a graduate student to tackle fundamental scientific problems using the state-of-the-art experimental techniques in the high-pressure research laboratories at U. Michigan and the Advanced Photon Source (APS) at the Argonne National Laboratory (ANL). The proposed activity will enhance the infrastructure for research and education through collaborative projects at regional and national facilities including the Geophysical Laboratory, APS, and National Nanotechnology Infrastructure Network (NNIN). The project will produce calibration standards for the community to support carbon-related research. The proposal will involve female researchers and provide partial support for Dr. Chen as a new PI. The PIs will continue to actively disseminate research results broadly through publications, national and international meetings, the Internet, and news media.