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Re-Evaluating the Age of Deep Biosphere Fossils in the Lockne Impact Structure

1
Department of Biology and Environmental Science, Linnaeus University, 392 31 Kalmar, Sweden
2
Department of Earth Sciences, University of Gothenburg, Box 460, 40530 Göteborg, Sweden
3
Department of Biology, University of Southern Denmark, Campusvej 55, 5230 Odense, Denmark
4
Department of Paleobiology, Swedish Museum of Natural History, Box 50 007, 104 05 Stockholm, Sweden
5
Department of Geosciences, Swedish Museum of Natural History, Box 50 007, 104 05 Stockholm, Sweden
*
Author to whom correspondence should be addressed.
Geosciences 2019, 9(5), 202; https://doi.org/10.3390/geosciences9050202
Received: 15 March 2019 / Revised: 26 April 2019 / Accepted: 4 May 2019 / Published: 7 May 2019
(This article belongs to the Special Issue Tracking the Deep Biosphere through Time)
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Abstract

Impact-generated hydrothermal systems have been suggested as favourable environments for deep microbial ecosystems on Earth, and possibly beyond. Fossil evidence from a handful of impact craters worldwide have been used to support this notion. However, as always with mineralized remains of microorganisms in crystalline rock, certain time constraints with respect to the ecosystems and their subsequent fossilization are difficult to obtain. Here we re-evaluate previously described fungal fossils from the Lockne crater (458 Ma), Sweden. Based on in-situ Rb/Sr dating of secondary calcite-albite-feldspar (356.6 ± 6.7 Ma) we conclude that the fungal colonization took place at least 100 Myr after the impact event, thus long after the impact-induced hydrothermal activity ceased. We also present microscale stable isotope data of 13C-enriched calcite suggesting the presence of methanogens contemporary with the fungi. Thus, the Lockne fungi fossils are not, as previously thought, related to the impact event, but nevertheless have colonized fractures that may have been formed or were reactivated by the impact. Instead, the Lockne fossils show similar features as recent findings of ancient microbial remains elsewhere in the fractured Swedish Precambrian basement and may thus represent a more general feature in this scarcely explored habitat than previously known. View Full-Text
Keywords: Impact structure; fungal hyphae; in situ radiometric dating; secondary minerals; stable isotopes Impact structure; fungal hyphae; in situ radiometric dating; secondary minerals; stable isotopes
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Tillberg, M.; Ivarsson, M.; Drake, H.; Whitehouse, M.J.; Kooijman, E.; Schmitt, M. Re-Evaluating the Age of Deep Biosphere Fossils in the Lockne Impact Structure. Geosciences 2019, 9, 202.

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