Because all known Eoarchean (>3.65 Ga) volcano-sedimentary terranes are locked in granitoid gneiss complexes that have experienced high degrees of metamorphism and deformation, the origin and mode of preservation of carbonaceous material in the oldest metasedimentary rocks remain a subject of vigorous debate. To determine the biogenicity of carbon in graphite in such rocks, carbonaceous material must be demonstrably indigenous and its composition should be consistent with thermally altered biogenic carbon as well as inconsistent with abiogenic carbon. Here we report the petrological and spectroscopic characteristics of carbonaceous material, typically associated with individual apatite grains, but also with various other minerals including calcite, in a >3.83 Ga granulite-facies ferruginous quartz-pyroxene unit (Qp rock) from the island of Akilia in southern West Greenland. In thin sections of the fine-grained parts of Akilia Qp rock sample G91-26, mapped apatites were found to be associated with graphite in about 20% of the occurrences. Raman spectra of this carbonaceous material had strong G-band and small D-band absorptions indicative of crystalline graphite. Three apatite-associated graphites were found to contain curled graphite structures, identified by an anomalously intense second-order D-band (or 2D-band) Raman mode. These structures are similar to graphite whiskers or cones documented to form at high temperatures. Raman spectra of apatite-associated graphite were consistent with formation at temperatures calculated to be between 635 and 830 degrees C, which are consistent with granulite-facies metamorphic conditions. Three graphite targets extracted by focused ion beam (FIB) methods contained thin graphite coatings on apatite grains rather than inclusions sensu stricto as inferred from transmitted light microscopy and Raman spectroscopy. TEM analyses of graphite in these FIB sections showed a (0 0 0 2) interplanar spacing between 3.41 and 3.64 angstrom for apatite-associated graphite, which is larger than the spacing of pure graphite (3.35 angstrom) and may be caused by the presence of non-carbon heteroatoms in inter-layer sites. Samples analyzed by synchrotron-based scanning transmission X-ray microscopy (STXM) also confirmed the presence of crystalline graphite, but abundances of N and O heteroatoms were below detection limit for this method. Graphite in the Akilia Qp rock was also found to occur in complex polyphase mineral assemblages of hornblende +/- calcite +/- sulfides +/- magnetite that point to high-temperature precipitation from carbon-bearing fluids. These complex mineral assemblages may represent another generation of graphitization that could have occurred during the amphibolite-facies metamorphic event at 2.7 Ga. Several observations point to graphitization from high-temperature fluid-deposition for some of the Akilia graphite and our results do not exclude a biogenic source of carbon in graphite associated with apatite, but ambiguities remain for the origin of this carbon. (C) 2010 Elsevier Ltd. All rights reserved.

Because all known Eoarchean (>3.65 Ga) volcano-sedimentary terranes are locked in granitoid gneiss complexes that have experienced high degrees of metamorphism and deformation, the origin and mode of preservation of carbonaceous material in the oldest metasedimentary rocks remain a subject of vigorous debate. To determine the biogenicity of carbon in graphite in such rocks, carbonaceous material must be demonstrably indigenous and its composition should be consistent with thermally altered biogenic carbon as well as inconsistent with abiogenic carbon. Here we report the petrological and spectroscopic characteristics of carbonaceous material, typically associated with individual apatite grains, but also with various other minerals including calcite, in a >3.83 Ga granulite-facies ferruginous quartz-pyroxene unit (Qp rock) from the island of Akilia in southern West Greenland. In thin sections of the fine-grained parts of Akilia Qp rock sample G91-26, mapped apatites were found to be associated with graphite in about 20% of the occurrences. Raman spectra of this carbonaceous material had strong G-band and small D-band absorptions indicative of crystalline graphite. Three apatite-associated graphites were found to contain curled graphite structures, identified by an anomalously intense second-order D-band (or 2D-band) Raman mode. These structures are similar to graphite whiskers or cones documented to form at high temperatures. Raman spectra of apatite-associated graphite were consistent with formation at temperatures calculated to be between 635 and 830 degrees C, which are consistent with granulite-facies metamorphic conditions. Three graphite targets extracted by focused ion beam (FIB) methods contained thin graphite coatings on apatite grains rather than inclusions sensu stricto as inferred from transmitted light microscopy and Raman spectroscopy. TEM analyses of graphite in these FIB sections showed a (0 0 0 2) interplanar spacing between 3.41 and 3.64 angstrom for apatite-associated graphite, which is larger than the spacing of pure graphite (3.35 angstrom) and may be caused by the presence of non-carbon heteroatoms in inter-layer sites. Samples analyzed by synchrotron-based scanning transmission X-ray microscopy (STXM) also confirmed the presence of crystalline graphite, but abundances of N and O heteroatoms were below detection limit for this method. Graphite in the Akilia Qp rock was also found to occur in complex polyphase mineral assemblages of hornblende +/- calcite +/- sulfides +/- magnetite that point to high-temperature precipitation from carbon-bearing fluids. These complex mineral assemblages may represent another generation of graphitization that could have occurred during the amphibolite-facies metamorphic event at 2.7 Ga. Several observations point to graphitization from high-temperature fluid-deposition for some of the Akilia graphite and our results do not exclude a biogenic source of carbon in graphite associated with apatite, but ambiguities remain for the origin of this carbon. (C) 2010 Elsevier Ltd. All rights reserved.

Model compound chitin and invertebrate cuticles were analysed using pyrolysis-gas chromatography-mass spectrometry, (13) C NMR and C-, N-, and O-Xray Absorption Near Edge Structure (XANES) spectral imaging using Scanning Transmission X-ray Microscopy (STXM) to detect spectra that are characteristic of chitin. Acetylpyridones, acetamidofuran, 3-acetamido-5-methylfuran and 3-acetamido-(2 and 4)-pyrones appear to be characteristic pyrolysis products for chitin. Pyrolysis products with ions of m/z 70, 154, 168, 194 likely derive from diketopiperazine structures and provide potential markers for proteins and peptides in which proline, alanine, valine, arginine and glycine are the dominant amino acids. The C-13 NMR spectra of chitin reveals that amidyl methyl group resonates at 23 ppm, amidyl linked glyocosyl carbon resonates at 56 ppm, glucosyl secondary alcohols resonate between 62 and 84 ppm, and glycosidic carbon absorption is evident at similar to 105 ppm. The presence of protein in the arthropod cuticles is evident by resonance intensity associated with sp(2) bonded carbon associated in unsaturated amino acids (e.g. phenyl alanine, tyrosine, and histidine) occurring at 116, 129, and 137 ppm. Additionally, the protein back bone methine carbon atoms are indicated by resonance intensity at 43 ppm. Additional broad resonance intensity in the 20-30 ppm range is derived both from aliphatic aminoacids (e.g. valine and leucine) as well as the fatty acids associated with the waxy cuticulin layer of the cuticle. High energy resolution C-, N-, and O-XANES spectra provide further functional group level characterization of the biomacromolecular assemblages at spatial scales on the order of 100's of nm. Combining the power of Solid state C-13 NMR, pyrolysis with the micro-analytical capabilities of C-, N-, and O-XANES yields a formidable analytical approach towards detecting and quantitating the presence of chitin in complex biomacromolecular assemblages.

Model compound chitin and invertebrate cuticles were analysed using pyrolysis-gas chromatography-mass spectrometry, (13) C NMR and C-, N-, and O-Xray Absorption Near Edge Structure (XANES) spectral imaging using Scanning Transmission X-ray Microscopy (STXM) to detect spectra that are characteristic of chitin. Acetylpyridones, acetamidofuran, 3-acetamido-5-methylfuran and 3-acetamido-(2 and 4)-pyrones appear to be characteristic pyrolysis products for chitin. Pyrolysis products with ions of m/z 70, 154, 168, 194 likely derive from diketopiperazine structures and provide potential markers for proteins and peptides in which proline, alanine, valine, arginine and glycine are the dominant amino acids. The C-13 NMR spectra of chitin reveals that amidyl methyl group resonates at 23 ppm, amidyl linked glyocosyl carbon resonates at 56 ppm, glucosyl secondary alcohols resonate between 62 and 84 ppm, and glycosidic carbon absorption is evident at similar to 105 ppm. The presence of protein in the arthropod cuticles is evident by resonance intensity associated with sp(2) bonded carbon associated in unsaturated amino acids (e.g. phenyl alanine, tyrosine, and histidine) occurring at 116, 129, and 137 ppm. Additionally, the protein back bone methine carbon atoms are indicated by resonance intensity at 43 ppm. Additional broad resonance intensity in the 20-30 ppm range is derived both from aliphatic aminoacids (e.g. valine and leucine) as well as the fatty acids associated with the waxy cuticulin layer of the cuticle. High energy resolution C-, N-, and O-XANES spectra provide further functional group level characterization of the biomacromolecular assemblages at spatial scales on the order of 100's of nm. Combining the power of Solid state C-13 NMR, pyrolysis with the micro-analytical capabilities of C-, N-, and O-XANES yields a formidable analytical approach towards detecting and quantitating the presence of chitin in complex biomacromolecular assemblages.

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.