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Nat Commun. 2017 Jun 1;8:15702. doi: 10.1038/ncomms15702.

Tracing the oxygen isotope composition of the upper Earth's atmosphere using cosmic spherules.

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Universität Göttingen, Geowissenschaftliches Zentrum, Goldschmidtstraße 1, 37077 Göttingen, Germany.
Karlsruher Institut für Technologie, Institut für Angewandte Materialien - Werkstoffprozesstechnik, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany.
Universität Köln, Institut für Geologie und Mineralogie, Greinstraße 4-6, 50939 Köln, Germany.
Universitá di Pisa, Dipartimento di Scienze della Terra, Via Santa Maria 53, 56126 Pisa, Italy.


Molten I-type cosmic spherules formed by heating, oxidation and melting of extraterrestrial Fe,Ni metal alloys. The entire oxygen in these spherules sources from the atmosphere. Therefore, I-type cosmic spherules are suitable tracers for the isotopic composition of the upper atmosphere at altitudes between 80 and 115 km. Here we present data on I-type cosmic spherules collected in Antarctica. Their composition is compared with the composition of tropospheric O2. Our data suggest that the Earth's atmospheric O2 is isotopically homogenous up to the thermosphere. This makes fossil I-type micrometeorites ideal proxies for ancient atmospheric CO2 levels.

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