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Published February 2018 | Published + Supplemental Material
Journal Article Open

Archean kerogen as a new tracer of atmospheric evolution: Implications for dating the widespread nature of early life

Abstract

Understanding the composition of the Archean atmosphere is vital for unraveling the origin of volatiles and the environmental conditions that led to the development of life. The isotopic composition of xenon in the Archean atmosphere has evolved through time by mass-dependent fractionation from a precursor comprising cometary and solar/chondritic contributions (referred to as U-Xe). Evaluating the composition of the Archean atmosphere is challenging because limited amounts of atmospheric gas are trapped within minerals during their formation. We show that organic matter, known to be efficient at preserving large quantities of noble gases, can be used as a new archive of atmospheric noble gases. Xe isotopes in a kerogen isolated from the 3.0–billion-year–old Farrel Quartzite (Pilbara Craton, Western Australia) are mass fractionated by 9.8 ± 2.1 per mil (‰) (2σ) per atomic mass unit, in line with a progressive evolution toward modern atmospheric values. Archean atmospheric Xe signatures in kerogens open a new avenue for following the evolution of atmospheric composition through time. The degree of mass fractionation of Xe isotopes relative to the modern atmosphere can provide a time stamp for dating Archean kerogens and therefore narrowing the time window for the diversification of early life during the Archean eon.

Additional Information

© 2018 The Authors. This is an open-access article distributed under the terms of the Creative Commons Attribution-NonCommercial license, which permits use, distribution, and reproduction in any medium, so long as the resultant use is not for commercial advantage and provided the original work is properly cited. Submitted 16 October 2017. Accepted 30 January 2018. Published 28 February 2018. We thank L. Zimmermann, Y. Marrocchi, and K. Zahnle for fruitful discussions. We also thank V. Rouchon and O. Belhadj (Center for Research on the Preservation of Collections, USR 3224) for Raman microspectroscopy. Funding: This study was supported by the European Research Council (grants PaleoNanoLife 2011-ADG_20110209 to F.R. and PHOTONIS 695618 to B.M.). This is Centre de Recherches Pétrographiques et Géochimiques–CNRS contribution #2549. Author contributions: D.V.B. did the noble gas analyses, discussed the results and their interpretations, and wrote the manuscript. M.W.B. participated in the noble gas analyses, discussed the results and their interpretations, and participated in writing the manuscript. F.D. did the IOM isolation from the MGTKS3 black chert sample, performed Raman analyses, discussed the interpretations, and participated in writing the manuscript. G.A., F.R., and B.M. discussed the results and their interpretations and participated in writing the manuscript. The authors declare that they have no competing interests.

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