Letter | Published:

Elements of Eoarchean life trapped in mineral inclusions

Nature volume 548, pages 7881 (03 August 2017) | Download Citation


Metasedimentary rocks from Isua, West Greenland (over 3,700 million years old) contain 13C-depleted carbonaceous compounds, with isotopic ratios that are compatible with a biogenic origin1,2,3. Metamorphic garnet crystals in these rocks contain trails of carbonaceous inclusions that are contiguous with carbon-rich sedimentary beds in the host rock, where carbon is fully graphitized. Previous studies4,5 have not been able to document other elements of life (mainly hydrogen, oxygen, nitrogen and phosphorus) structurally bound to this carbonaceous material. Here we study carbonaceous inclusions armoured within garnet porphyroblasts, by in situ infrared absorption on approximately 10−21 m3 domains within these inclusions. We show that the absorption spectra are consistent with carbon bonded to nitrogen and oxygen, and probably also to phosphate. The levels of C–H or O–H bonds were found to be low. These results are consistent with biogenic organic material isolated for billions of years and thermally matured at temperatures of around 500 °C. They therefore provide spatial characterization for potentially the oldest biogenic carbon relics in Earth’s geological record. The preservation of Eoarchean organic residues within sedimentary material corroborates earlier claims2,6 for the biogenic origins of carbon in Isua metasediments.

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The research was supported by the Danish National Research Foundation (DNRF; fund number DNRF53) to Nordic Center for Earth Evolution. The research was supported by the NanoGeoScience group. We are grateful to E. Mathez, S. L. S. Stipp, J. Generosi and K. Bechgaard for inspiring discussions and J. Andersen for establishing contact. We also wish to thank D. Buti for assistance with the Raman spectroscopy.

Author information


  1. Nano-Science Center, Department of Chemistry, University of Copenhagen, Copenhagen 2100, Denmark

    • T. Hassenkam
    • , M. P. Andersson
    •  & K. N. Dalby
  2. Center for Nanostructured Graphene (CNG), Department of Micro- and Nanotechnology, Technical University of Denmark, Kongens Lyngby 2800, Denmark

    • D. M. A. Mackenzie
  3. Natural History Museum of Denmark, University of Copenhagen, Copenhagen 1350, Denmark

    • M. T. Rosing


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T.H. and M.T.R. conceived the idea for this study. M.T.R. collected, dated and isolated the individual garnet crystals and discovered the inclusions. M.T.R. made the optical transmission images of the garnets in their bedding. T.H. developed the method for accessing the inclusions with the AFM-IR. T.H. did the AFM-IR measurements and the assignment of IR absorption peaks to chemical bonds. The interpretation of the data where done mostly by M.T.R. and T.H. M.P.A. and K.N.D. confirmed the assignment of the IR absorption peaks. K.N.D. made and interpreted the SEM pictures and the EDXS maps. M.P.A. performed the modelling. D.M.A.M. did the Raman mapping. T.H. and D.M.A.M. analysed the result. T.H. wrote the paper with input from all authors. All authors contributed to scientific discussions.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to T. Hassenkam.

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Extended data

Supplementary information

PDF files

  1. 1.

    Supplementary Information

    This file contains information on geological context broken down into protolith, age, metamorphism, and deformation and also includes an analysis of the molecular modelling. The file also contains supplementary table 3 which shows the IR absorption assignment.

Excel files

  1. 1.

    Supplementary Table

    This file contains supplementary table 1 which shows the major elements in the metasedimentary rock. The inclusions studied are from 30048.

  2. 2.

    Supplementary Table

    This file contains supplementary table 2 which shows composition data in biotite and garnets at various positions close to the inclusions studied. Also shown is the estimated temperature using a calibration by Ferry and Spear.

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