Hatte der Mars vor 4 Milliarden Jahren eine sauerstoffreiche Atmosphäre?

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Hatte der Mars vor 4 Milliarden Jahren eine sauerstoffreiche Atmosphäre?

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Supplementary information

Detailed information about the chemical composition and evolution of Mars has been derived principally from the SNC (shergottite–nakhlite–chassignite) meteorites, which are genetically related igneous rocks of Martian origin1, 2. They are chemically and texturally similar to terrestrial basalts and cumulates, except that they have higher concentrations of iron and volatile elements such as phosphorus and chlorine and lower concentrations of nickel and other chalcophile (sulphur-loving) elements3. Most Martian meteorites have relatively young crystallization ages (1.4 billion years to 180 million years ago4) and are considered to be derived from young, lightly cratered volcanic regions, such as the Tharsis plateau4, 5. Surface rocks from the Gusev crater analysed by the Spirit rover are much older (about 3.7 billion years old6) and exhibit marked compositional differences from the meteorites7. Although also basaltic in composition, the surface rocks are richer in nickel and sulphur and have lower manganese/iron ratios than the meteorites. This has led to doubts that Mars can be described adequately using the ‘SNC model’. Here we show, however, that the differences between the compositions of meteorites and surface rocks can be explained by differences in the oxygen fugacity during melting of the same sulphur-rich mantle. This ties the sources of Martian meteorites to those of the surface rocks through an early (>3.7 billion years ago) oxidation of the uppermost mantle that had less influence on the deeper regions, which produce the more recent volcanic rocks.

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Hier ist noch ein akustischer Beitrag des Nature Magazins (20.6.13)

Der relevante Beitrag zum Artikel von Tuff et al. beginnt bei 13:30 und endet bei 18:56 Min. Laufzeit.

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The red planet's past
Martian rock records suggest Mars had plenty in common with Earth, back in the day

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Neues zur frühen Marsatmosphäre:

Die umfangreiche Analyse von Schwefelisotopen in 40 Marsmeteoriten gibt neue Hinweise auf die Besonderheiten des Schwefelkreislaufs auf dem Mars

Meteorites yield clues to red planet's early atmosphere

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Isotopic links between atmospheric chemistry and the deep sulphur cycle on Mars

Heather B. Franz, Sang-Tae Kim , James Farquhar ,  James M. D. Day, Rita C. Economos,
Kevin D. McKeegan, Axel K. Schmitt, Anthony J. Irving, Joost Hoek, James Dottin III,

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Nature 508, 364–368 (17 April 2014) doi:10.1038/nature13175

Zusammenfassung:
Many questions remain regarding the surface processes operating on Mars and the magmatic assimilation of crustal material, and sulphur chemistry is crucial to these and other phenomena on the planet. A new sulphur isotope analysis of 40 Martian meteorites now suggests an atmospheric sulphur chemistry, notably the photochemical processing preserved in meteoritic sulphide and sulphate, very different from that seen on Earth. The data provide evidence to suggest that the assimilation of sulphur into Martian magmas was a common occurrence throughout much of the planet's history. The authors conclude that sulphur isotope systematics, used in conjunction with data for other isotopic systems and trace element characteristics, is a powerful tool for reconstructing the geological history of Mars.

The geochemistry of Martian meteorites provides a wealth of information about the solid planet and the surface and atmospheric processes that occurred on Mars. The degree to which Martian magmas may have assimilated crustal material, thus altering the geochemical signatures acquired from their mantle sources, is unclear. This issue features prominently in efforts to understand whether the source of light rare-earth elements in enriched shergottites lies in crustal material incorporated into melts or in mixing between enriched and depleted mantle reservoirs. Sulphur isotope systematics offer insight into some aspects of crustal assimilation. The presence of igneous sulphides in Martian meteorites with sulphur isotope signatures indicative of mass-independent fractionation suggests the assimilation of sulphur both during passage of magmas through the crust of Mars and at sites of emplacement. Here we report isotopic analyses of 40 Martian meteorites that represent more than half of the distinct known Martian meteorites, including 30 shergottites (28 plus 2 pairs, where pairs are separate fragments of a single meteorite), 8 nakhlites (5 plus 3 pairs), Allan Hills 84001 and Chassigny. Our data provide strong evidence that assimilation of sulphur into Martian magmas was a common occurrence throughout much of the planet’s history. The signature of mass-independent fractionation observed also indicates that the atmospheric imprint of photochemical processing preserved in Martian meteoritic sulphide and sulphate is distinct from that observed in terrestrial analogues, suggesting fundamental differences between the dominant sulphur chemistry in the atmosphere of Mars and that in the atmosphere of Earth.

Detaillierte Ergebnisse zu einzelnen Marsmeteoriten sind hier zu finden:

Supplementary Information (PDF / 1.1 MB)