Abstract
Understanding the origin of organic material on Mars is a major issue in modern planetary science. Recent robotic exploration of Martian sedimentary rocks and laboratory analyses of Martian meteorites have both reported plausible indigenous organic components. However, little is known about their origin, evolution, and preservation. Here we report that 4-billion-year-old (Ga) carbonates in Martian meteorite, Allan Hills 84001, preserve indigenous nitrogen(N)-bearing organics by developing a new technique for high-spatial resolution in situ N-chemical speciation. The organic materials were synthesized locally and/or delivered meteoritically on Mars during Noachian age. The carbonates, alteration minerals from the Martian near-surface aqueous fluid, trapped and kept the organic materials intact over long geological times. This presence of N-bearing compounds requires abiotic or possibly biotic N-fixation and ammonia storage, suggesting that early Mars had a less oxidizing environment than today.
Highlights
Understanding the origin of organic material on Mars is a major issue in modern planetary science
In this study we demonstrated for the first time the presence of trapped N-bearing organic compounds from micrometer-scale in situ analysis of N K-edge micro X-ray absorption near-edge structure (μ-XANES) on the 4 Ga Allan Hills (ALH) carbonates
The XANES spectra indicate the presence of indigenous N-bearing organics, which may have been trapped in ALH carbonates on Noachian Mars and preserved since
Summary
Understanding the origin of organic material on Mars is a major issue in modern planetary science. Because ALH carbonates are considered to have precipitated via a low-temperature aqueous alteration at 4.04–3.90 Ga at Martian near-surface[18,19], their organic records, if any, should reflect the geochemical conditions at Noachian Mars. In this study we demonstrated for the first time the presence of trapped N-bearing organic compounds from micrometer-scale in situ analysis of N K-edge micro X-ray absorption near-edge structure (μ-XANES) on the 4 Ga ALH carbonates.
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