Letter

Early trace of life from 3.95 Ga sedimentary rocks in Labrador, Canada

  • Nature volume 549, pages 516518 (28 September 2017)
  • doi:10.1038/nature24019
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Abstract

The vestiges of life in Eoarchean rocks have the potential to elucidate the origin of life. However, gathering evidence from many terrains is not always possible1,2,3, and biogenic graphite has thus far been found only in the 3.7–3.8 Ga (gigayears ago) Isua supracrustal belt4,5,6,7. Here we present the total organic carbon contents and carbon isotope values of graphite (δ13Corg) and carbonate (δ13Ccarb) in the oldest metasedimentary rocks from northern Labrador8,9. Some pelitic rocks have low δ13Corg values of −28.2, comparable to the lowest value in younger rocks. The consistency between crystallization temperatures of the graphite and metamorphic temperature of the host rocks establishes that the graphite does not originate from later contamination. A clear correlation between the δ13Corg values and metamorphic grade indicates that variations in the δ13Corg values are due to metamorphism, and that the pre-metamorphic value was lower than the minimum value. We concluded that the large fractionation between the δ13Ccarb and δ13Corg values, up to 25‰, indicates the oldest evidence of organisms greater than 3.95 Ga. The discovery of the biogenic graphite enables geochemical study of the biogenic materials themselves, and will provide insight into early life not only on Earth but also on other planets.

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Acknowledgements

This research was supported by the Ministry of Education, Culture, Sports, Science and Technology, Japan (grant numbers: 23253007, 26220713 and 24221002) and the Mitsubishi Foundation. We thank K. D. Collerson and B. Ryan for sharing their geological information. We are grateful to W. Broomfield, Parks Canada, Labrador Inuit Development Corporation (LIDC) and many bear monitors who assisted with our geological fieldwork at the Saglek Block.

Author information

Author notes

    • Yuji Sano
    •  & Tsuyoshi Komiya

    These authors jointly supervised this work.

Affiliations

  1. Department of Earth Science and Astronomy, Graduate School of Arts and Sciences, The University of Tokyo, Tokyo 153-8902, Japan

    • Takayuki Tashiro
    •  & Tsuyoshi Komiya
  2. Atmosphere and Ocean Research Institute, The University of Tokyo, Chiba 277-8564, Japan

    • Akizumi Ishida
    • , Masako Hori
    • , Mizuho Koike
    • , Pauline Méjean
    • , Naoto Takahata
    •  & Yuji Sano
  3. Institute for Excellence in Higher Education, Tohoku University, Sendai 9808576, Japan

    • Akizumi Ishida
  4. Department of Arts and Sciences, Osaka Kyoiku University, Osaka 582-8582, Japan

    • Masako Hori
  5. Laboratory of Ocean-Earth Life Evolution Research, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Kanagawa 237-0061, Japan

    • Motoko Igisu

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Contributions

T.K. designed the study and Y.S. designed the geochemical study. T.K., T.T., A.I., M.H., M.I., M.K., P.M., N. T., and Y.S. conducted geochemical analyses. T.K. and T.T. collected samples in the field. T.K. wrote the manuscript with important contributions from all co-authors.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Tsuyoshi Komiya.

Reviewer Information Nature thanks A. Polat and the other anonymous reviewer(s) for their contribution to the peer review of this work.

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