Reassessing the evidence for the earliest traces of life

The isotopic composition of graphite is commonly used as a biomarker in the oldest (>3.5 Gyr ago) highly metamorphosed terrestrial rocks. Earlier studies on isotopic characteristics of graphite occurring in rocks of the approximately 3.8-Gyr-old Isua supracrustal belt (ISB) in southern West Greenland have suggested the presence of a vast microbial ecosystem in the early Archean. This interpretation, however, has to be approached with extreme care. Here we show that graphite occurs abundantly in secondary carbonate veins in the ISB that are formed at depth in the crust by injection of hot fluids reacting with older crustal rocks (metasomatism). During these reactions, graphite forms from the disproportionation of Fe(II)-bearing carbonates at high temperature. These metasomatic rocks, which clearly lack biological relevance, were earlier thought to be of sedimentary origin and their graphite association provided the basis for inferences about early life. The new observations thus call for a reassessment of previously presented evidence for ancient traces of life in the highly metamorphosed Early Archaean rock record.

[1]  Manfred Schidlowski,et al.  Carbon isotopes as biogeochemical recorders of life over 3.8 Ga of Earth history: evolution of a concept , 2001 .

[2]  S. Ahmad,et al.  Carbon isotope composition of graphite and carbonate minerals from 3.8-AE metamorphosed sediments, Isukasia, Greenland , 1977 .

[3]  R. F. Dymek,et al.  Metamorphism of the ca. 3800 Ma supracrustal rocks at Isua, West Greenland: implications for early Archaean crustal evolution , 1982 .

[4]  T. Hunt,et al.  The proteolysis of mitotic cyclins in mammalian cells persists from the end of mitosis until the onset of S phase. , 1996, The EMBO journal.

[5]  H. Yurimoto,et al.  Ion microprobe analysis of graphite from ca. 3.8 Ga metasediments, Isua supracrustal belt, West Greenland: Relationship between metamorphism and carbon isotopic composition , 2002 .

[6]  Howard Cedar,et al.  DNA methylation represses transcription in vivo , 1999, Nature Genetics.

[7]  M. Rosing,et al.  The role of ultramafic rocks in regulating the concentrations of volatile and non-volatile components during deep crustal metamorphism , 1993 .

[8]  C. Klein,et al.  Chemistry, petrology and origin of banded iron-formation lithologies from the 3800 MA isua supracrustal belt, West Greenland , 1988 .

[9]  M. Rosing,et al.  13C-Depleted carbon microparticles in >3700-Ma sea-floor sedimentary rocks from west greenland , 1999, Science.

[10]  K. D. McKeegan,et al.  Evidence for life on Earth before 3,800 million years ago , 1996, Nature.

[11]  M. Schidlowski.  A 3,800-million-year isotopic record of life from carbon in sedimentary rocks , 1988, Nature.

[12]  B. French.  Stability relations of siderite (FeCO 3 ) in the system Fe-C-O , 1971 .

[13]  John M. Hayes,et al.  The earliest memories of life on Earth , 1996, Nature.

[14]  J. Myers.  Protoliths of the 3.8-3.7 Ga Isua greenstone belt, West Greenland , 2001 .

[15]  T. R. Hebbes,et al.  Core histone hyperacetylation co‐maps with generalized DNase I sensitivity in the chicken beta‐globin chromosomal domain. , 1994, The EMBO journal.

[16]  I. Simon,et al.  Asynchronous replication of imprinted genes is established in the gametes and maintained during development , 1999, Nature.

[17]  D. Oehler,et al.  Isotopic composition of reduced and oxidized carbon in early Archaean rocks from Isua, Greenland , 1977 .

[18]  G. Arrhenius,et al.  Apatite in early Archean Isua supracrustal rocks, southern West Greenland: its origin, association with graphite and potential as a biomarker , 2002 .

[19]  M. Rosing,et al.  Stratigraphic and geochemical evidence for the depositional environment of the early Archaean Isua supracrustal belt, southern West Greenland , 1984 .

[20]  M. Whitehouse,et al.  Metasomatic Origin of Quartz-Pyroxene Rock, Akilia, Greenland, and Implications for Earth's Earliest Life , 2002, Science.

[21]  M. Schidlowski,et al.  Carbon isotope geochemistry of the 3.7 × 109-yr-old Isua sediments, West Greenland: implications for the Archaean carbon and oxygen cycles , 1979 .

[22]  C. Fedo,et al.  Depositional setting and paleogeographic implications of earth's oldest supracrustal rocks, the >3.7 Ga Isua Greenstone belt, West Greenland , 2001 .

[23]  S. Newman,et al.  CO 2 , 13 C/ 12 C and H 2 O variability in natural basaltic glasses: a study comparing stepped heating and ftir spectroscopic techniques , 1999 .

[24]  M. Rosing,et al.  The origin of metacarbonate rocks in the Archaean Isua supracrustal belt, West Greenland , 1996 .

[25]  J. L. Teranes,et al.  Graphite and carbonates in the 3.8 Ga old Isua Supracrustal Belt, southern West Greenland , 2003 .

[26]  J. Diffley,et al.  A Mec1- and Rad53-dependent checkpoint controls late-firing origins of DNA replication , 1998, Nature.

[27]  B. Nagy.  Porosity and permeability of the early precambrian onverwacht chert: Origin of the hydrocarbon content , 1970 .

[28]  I. Jarvis,et al.  Phosphorite research and development , 1990 .

[29]  R. Clayton,et al.  Oxygen and carbon isotope fractionations between CO2 and calcite , 1991 .

[30]  J. William Schopf,et al.  Earth's earliest biosphere : its origin and evolution , 1983 .

[31]  M. Botchan,et al.  Activation of BPV-1 replication in vitro by the transcription factor E2 , 1991, Nature.

[32]  Appel,et al.  Recognizable primary volcanic and sedimentary features in a low‐strain domain of the highly deformed, oldest known (≈ 3.7–3.8 Gyr) Greenstone Belt, Isua, West Greenland , 1998 .

[33]  P. Appel.  On the early archaean isua iron-formation, West Greenland , 1980 .

[34]  K. Shirahige,et al.  Regulation of DNA-replication origins during cell-cycle progression , 1998, Nature.

[35]  M. Rosing,et al.  Earliest part of Earth's stratigraphic record: A reappraisal of the >3.7 Ga Isua (Greenland) supracrustal sequence , 1996 .

[36]  A. Graessmann,et al.  Microinjection of tissue culture cells. , 1983, Methods in enzymology.

[37]  F. Cross,et al.  CLB5-dependent activation of late replication origins in S. cerevisiae. , 1998, Molecular cell.