LECOR · Light elements in the core

Since the discovery of the Earth’s internal structure and the existence of a dense metallic core about a century ago, the idea of iron being the dominant component of the core gained firm support confirmed by cosmochemical and geochemical observations, seismic data, the theory of geomagnetism, and high-pressure studies. However, although closely matching, the velocities of seismic waves traveling through the core are significantly slower than those in a pure iron-nickel alloy. The observed core density- and velocity- deficit suggest that around 3-7 wt% of the light element(s) should be present in the inner core in order to explain the observed mismatch. Moreover, the inner core is anisotropic, with the compressional waves traveling faster along the polar axis than in the equatorial plane. Thus, the candidate material should be also able to explain the observed anisotropic pattern.Nonetheless, the nature of the light element(s) in the core remains unconstrained, with hydrogen, carbon, oxygen, silicon, and sulfur being the most plausible candidates. The laboratory measurements on the physical properties of some candidate materials at high pressures and room temperature are available in the literature, but data at simultaneous high pressures and temperatures as most relevant to the Earth core are almost absent.In LECOR, we aim to identify the most plausible candidate element, extending state-of-the-art measurement techniques considerably. In particular, we will study the elasticity and plastic deformation mechanisms of candidate binary and ternary iron alloys and compounds in situ at extreme pressure-temperature conditions using a combination of state-of-the-art synchrotron X-ray techniques developed in our group. We will interpret this novel data within the most recent geophysical and geochemical models, to better determine the composition of the Earth’s core. Such would open fascinating avenues to refine theories about the formation of planets, in general.