EGU General Assembly 2020
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

A Venus-like atmosphere on the early Earth from magma ocean outgassing

Paolo Sossi1,2, Antony Burnham3, James Badro2, Antonio Lanzirotti4, Matt Newville4, and Hugh O'Neill3
Paolo Sossi et al.
  • 1ETH Zurich, Institute of Geochemistry and Petrology, Earth Sciences, Zurich, Switzerland (
  • 2Institut de Physique du Globe de Paris, Universite de Paris, Paris, France
  • 3Research School of Earth Sciences, Australian National University, Canberra, Australia
  • 4Center for Advanced Radiation Sources, University of Chicago, Chicago, USA

Outgassing of an early magma ocean on Earth plays a dominant role in determining the composition of its secondary atmosphere, and hence bears on the potential for the emergence of life. The stability of gaseous species in such an atmosphere reflects the redox state of the magma ocean. However, the relationship between oxygen fugacity (fO2) and the oxidation state of the most abundant polyvalent element, Fe, in likely magma ocean compositions is poorly constrained. Here we determine Fe2+/Fe3+ ratios as a function of fO2 in peridotite liquids, experimentally synthesised by aerodynamic laser levitation at 1 bar and 2173 K. We show that a magma ocean with Fe3+/∑Fe akin to that of contemporary upper mantle peridotite (0.037) would have had fO2 0.5 log units higher than the Fe-“FeO” equilibrium. At this relative fO2, a neutral CO2-H2O-dominated atmosphere of ~ 150 bar would have developed on the early Earth, taking into account the solubilities of the major volatiles, H, C, N and O in the magma ocean. Upon cooling, the Earth’s prebiotic atmosphere was likely comprised of CO2-N2, in proportions and at pressures akin to that on presently found on Venus.

How to cite: Sossi, P., Burnham, A., Badro, J., Lanzirotti, A., Newville, M., and O'Neill, H.: A Venus-like atmosphere on the early Earth from magma ocean outgassing, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11217,, 2020.


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