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Oxidised micrometeorites as evidence for low atmospheric pressure on the early Earth

P.B. Rimmer1,2,3,

1Department of Earth Sciences, University of Cambridge, Cambridge, CB2 3EQ, UK
2Cavendish Astrophysics, University of Cambridge, JJ Thomson Avenue, Cambridge CB3 0HE, UK
3MRC Laboratory of Molecular Biology, Francis Crick Ave, Cambridge CB2 0QH, UK

O. Shorttle1,4,

1Department of Earth Sciences, University of Cambridge, Cambridge, CB2 3EQ, UK
4Institute of Astronomy, University of Cambridge, Cambridge, CB3 0HA, UK

S. Rugheimer5,6

5Centre for Exoplanets, School of Earth and Environmental Sciences, University of St. Andrews, Irvine Building, North Street, St. Andrews, KY16 9AL, UK
6Clarendon Laboratory, University of Oxford, Sherrington Road, Oxford, OX1 3PU, UK

Affiliations  |  Corresponding Author  |  Cite as  |  Funding information

Rimmer, P.B., Shorttle, O., Rugheimer, S. (2019) Oxidised micrometeorites as evidence for low atmospheric pressure on the early Earth. Geochem. Persp. Let. 9, 38–42.

Simons and Kavli Foundation (SCOL awards 599634 for PBR and SCOL awards 339489 for SR), and Trinity College Cambridge for OS.

Geochemical Perspectives Letters v9  |  doi: 10.7185/geochemlet.1903
Received 30 July 2018  |  Accepted 07 January 2019  |  Published 11 February 2019
Copyright © The Authors

Published by the European Association of Geochemistry
under Creative Commons License CC BY-NC-ND 4.0

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Table 1 Mixing ratios for two model atmospheres.
SpeciesCase 1Case 2
N20.330.33
CO20.330.66
CO0.333 x 10-6
H210-310-3
H2OVapour pressureVapour pressure
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Figure 1 Temperature profile for the Earth’s atmosphere with surface pressure of 0.3 bar composed of 33 % N2, 33 % CO2 and 33 % CO (dashed), and 33 % N2, 66 % CO2 (solid).
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Figure 2 Two low pressure model atmospheres of the 3.5 Ga 2.7 Ga Earth. One model includes a surface mixing ratio of CO of 0.33 (dashed), and the other a surface mixing ratio of 10-6 (solid). The surface pressure is 0.3 bar for both models. Mixing ratios are shown as a function of atmospheric height, h (km; top two figures) and pressure (bar; bottom two figures).
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Figure 3 The minimum O2/CO ratio suggested by the observed iron oxidation in 2.7 Ga micrometeorites (Tomkins et al. (2016)

Tomkins, A.G., Bowlt, L., Genge M., Wilson, S.A., Brand, H.E.A., Wykes, J.L. (2016) Ancient micrometeorites suggestive of an oxygen-rich Archaean upper atmosphere. Nature 533, 235–238.

), as a function of the melting temperature T [K]. Shaded regions show where there is sufficient O2 (light blue), sufficient temperature (light orange), and the overlap between these two regions (dark orange). The dotted line is the O2/CO ratio in the upper atmosphere for an anoxic atmosphere with a 1 bar surface pressure, and the dashed line is the O2/CO ratio in the upper atmosphere for an anoxic atmosphere with a 0.3 bar surface pressure.
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