The conventional geochemical view holds that the chitin and structural protein are not preserved in ancient fossils because they are readily degradable through microbial chitinolysis and proteolysis. Here we show a molecular signature of a relict chitin-protein complex preserved in a Pennsylvanian (310 Ma) scorpion cuticle and a Silurian (417 Ma) eurypterid cuticle via analysis with carbon, nitrogen, and oxygen X-ray absorption near edge structure (XANES) spectro-microscopy. High-resolution X-ray microscopy reveals the complex laminar variation in major biomolecule concentration across modern cuticle; XANES spectra highlight the presence of the characteristic functional groups of the chitin-protein complex. Modification of this complex is evident via changes in organic functional groups. Both fossil cuticles contain considerable aliphatic carbon relative to modern cuticle. However, the concentration of vestigial chitin-protein complex is high, 59% and 53% in the fossil scorpion and eurypterid, respectively. Preservation of a high-nitrogen-content chitin-protein residue in organic arthropod cuticle likely depends on condensation of cuticle-derived fatty acids onto a structurally modified chitin-protein molecular scaffold, thus preserving the remnant chitin-protein complex and cuticle from degradation by microorganisms.

The conventional geochemical view holds that the chitin and structural protein are not preserved in ancient fossils because they are readily degradable through microbial chitinolysis and proteolysis. Here we show a molecular signature of a relict chitin-protein complex preserved in a Pennsylvanian (310 Ma) scorpion cuticle and a Silurian (417 Ma) eurypterid cuticle via analysis with carbon, nitrogen, and oxygen X-ray absorption near edge structure (XANES) spectro-microscopy. High-resolution X-ray microscopy reveals the complex laminar variation in major biomolecule concentration across modern cuticle; XANES spectra highlight the presence of the characteristic functional groups of the chitin-protein complex. Modification of this complex is evident via changes in organic functional groups. Both fossil cuticles contain considerable aliphatic carbon relative to modern cuticle. However, the concentration of vestigial chitin-protein complex is high, 59% and 53% in the fossil scorpion and eurypterid, respectively. Preservation of a high-nitrogen-content chitin-protein residue in organic arthropod cuticle likely depends on condensation of cuticle-derived fatty acids onto a structurally modified chitin-protein molecular scaffold, thus preserving the remnant chitin-protein complex and cuticle from degradation by microorganisms.

The Mars Science Laboratory (MSL) has an instrument package capable of making measurements of past and present environmental conditions. The data generated may tell us if Mars is, or ever was, able to support life. However, the knowledge of Mars' past history and the geological processes most likely to preserve a record of that history remain sparse and, in some instances, ambiguous. Physical, chemical, and geological processes relevant to biosignature preservation on Earth, especially under conditions early in its history when microbial life predominated, are also imperfectly known. Here, we present the report of a working group chartered by the Co-Chairs of NASA's MSL Project Science Group, John P. Grotzinger and Michael A. Meyer, to review and evaluate potential for biosignature formation and preservation on Mars.

The Mars Science Laboratory (MSL) has an instrument package capable of making measurements of past and present environmental conditions. The data generated may tell us if Mars is, or ever was, able to support life. However, the knowledge of Mars' past history and the geological processes most likely to preserve a record of that history remain sparse and, in some instances, ambiguous. Physical, chemical, and geological processes relevant to biosignature preservation on Earth, especially under conditions early in its history when microbial life predominated, are also imperfectly known. Here, we present the report of a working group chartered by the Co-Chairs of NASA's MSL Project Science Group, John P. Grotzinger and Michael A. Meyer, to review and evaluate potential for biosignature formation and preservation on Mars.

Carbonaceous material present in ancient rocks can be used as an indicator of life during the time the rocks were formed. In particular, evidence for the existence of life more than 3,800 million years ago might come from mineral associations between apatite and graphite in rocks from southern West Greenland(1-7). However, this interpretation is partly based on the assumption that the graphite was formed at the same time as the host rocks, an assumption that has been difficult to prove(2-7). Here we investigate the origins of poorly crystalline graphite associated with apatite in metamorphosed banded iron formations from northern Canada that are 3,750 to 4,280 million years old(8-11). We measured average delta C-13(graphite) values of -22.8 +/- 1.9 parts per thousand(1 sigma), similar to values from West Greenland sedimentary rocks of comparable age(1,3,5-7,12-14), and that point to a biological source for this carbon. Our microscopic and spectroscopic analyses suggest, however, that the graphite experienced much lower temperatures than the host rocks during metamorphism. We conclude that the poorly crystalline graphite in these rocks was deposited by fluids after peak metamorphism of the banded iron formations. We suggest that the occurrence of carbonaceous material with low delta C-13 values in Eoarchaean rocks cannot be used to indicate the presence of a microbial biosphere on the earliest Earth unless the syngeneity of the carbonaceous material in the host rock can be confirmed.

Carbonaceous material present in ancient rocks can be used as an indicator of life during the time the rocks were formed. In particular, evidence for the existence of life more than 3,800 million years ago might come from mineral associations between apatite and graphite in rocks from southern West Greenland(1-7). However, this interpretation is partly based on the assumption that the graphite was formed at the same time as the host rocks, an assumption that has been difficult to prove(2-7). Here we investigate the origins of poorly crystalline graphite associated with apatite in metamorphosed banded iron formations from northern Canada that are 3,750 to 4,280 million years old(8-11). We measured average delta C-13(graphite) values of -22.8 +/- 1.9 parts per thousand(1 sigma), similar to values from West Greenland sedimentary rocks of comparable age(1,3,5-7,12-14), and that point to a biological source for this carbon. Our microscopic and spectroscopic analyses suggest, however, that the graphite experienced much lower temperatures than the host rocks during metamorphism. We conclude that the poorly crystalline graphite in these rocks was deposited by fluids after peak metamorphism of the banded iron formations. We suggest that the occurrence of carbonaceous material with low delta C-13 values in Eoarchaean rocks cannot be used to indicate the presence of a microbial biosphere on the earliest Earth unless the syngeneity of the carbonaceous material in the host rock can be confirmed.

The complex suite of organic materials in carbonaceous chondrite meteorites probably originally formed in the interstellar medium and/or the solar protoplanetary disk, but was subsequently modified in the meteorites' asteroidal parent bodies. The mechanisms of formation and modification are still very poorly understood. We carried out a systematic study of variations in the mineralogy, petrology, and soluble and insoluble organic matter in distinct fragments of the Tagish Lake meteorite. The variations correlate with indicators of parent body aqueous alteration. At least some molecules of prebiotic importance formed during the alteration.