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. 2015 Jun 2;112(22):6892-7.
doi: 10.1073/pnas.1421052112. Epub 2015 May 18.

Paleoarchean trace fossils in altered volcanic glass

Hubert Staudigel  1 , Harald Furnes  2 , Maarten DeWit  3
Affiliations

Paleoarchean trace fossils in altered volcanic glass

Hubert Staudigel et al. Proc Natl Acad Sci U S A. .

Abstract

Microbial corrosion textures in volcanic glass from Cenozoic seafloor basalts and the corresponding titanite replacement microtextures in metamorphosed Paleoarchean pillow lavas have been interpreted as evidence for a deep biosphere dating back in time through the earliest periods of preserved life on earth. This interpretation has been recently challenged for Paleoarchean titanite replacement textures based on textural and geochronological data from pillow lavas in the Hooggenoeg Complex of the Barberton Greenstone Belt in South Africa. We use this controversy to explore the strengths and weaknesses of arguments made in support or rejection of the biogenicity interpretation of bioalteration trace fossils in Cenozoic basalt glasses and their putative equivalents in Paleoarchean greenstones. Our analysis suggests that biogenicity cannot be taken for granted for all titanite-based textures in metamorphosed basalt glass, but a cautious and critical evaluation of evidence suggests that biogenicity remains the most likely interpretation for previously described titanite microtextures in Paleoarchean pillow lavas.

Keywords: Paleoarchean; astrobiology; biogeosciences; early life; ichnofossil.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig. 1.
Fig. 1.
Biotextures in fresh Cenozoic basalt glass and titanite microtextures in Archean greenschist pillow lavas. Comparison between tubular biotextures in (A) the 110-Ma-old deep sea drilling project (DSDP) sample 418A, 56–2, 129–132 cm, and (B) similarly shaped and sized tubular textures of the interpillow hyaloclastite (sample 29-BG-03) of the 3,470-Ma-old Hooggenoeg Complex. (C) DSDP sample 418A, 62–4, 64–70 cm, showing several dark brown varioles within the fresh glass and biogenerated filaments rooted in a fracture. (D) Figure S2F from ref. suggesting that some of these titanite microtextures may be varioles intermixed with tubular biotextures. (E) Details from sample 29-BG-03 from BGB (22) in which a 6-µm-wide tube, rooted in a titanite-filled fracture, may show a segmented nature. (F) Thin, 2–3-µm-wide segmented tubes extending from the edge of a former glass fragment (now mainly chlorite) from sample 74-PG-04 of the 3.35 Ga Euro Basalt of the PC, Western Australia (5).
Fig. 2.
Fig. 2.
Comparison between widths of tubular structures from (A) glassy margin of Cenozoic pillow lavas from in situ oceanic crust and titanite structures from the Hooggenoeg Complex. (B and C) Size of tubular structures rooted in fracture (A and B data are from ref. 22) and (C) filamentous and globular structures (unrelated to fractures) shown in figure 1I of ref. .
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References

    1. Furnes H, Staudigel H. Biological mediation in ocean crust alteration: How deep is the deep biosphere? Earth Planet Sci Lett. 1999;166(3-4):97–103.
    1. Staudigel H, et al. 3.5 billion years of glass bioalteration: Volcanic rocks as a basis for microbial life? Earth Sci Rev. 2008;89:156–176.
    1. Furnes H, Banerjee NR, Muehlenbachs K, Staudigel H, de Wit M. Early life recorded in Archean pillow lavas. Science. 2004;304(5670):578–581. - PubMed
    1. Banerjee NR, Furnes H, Muehlenbachs K, Staudigel H, de Wit M. Preservation of ∼3.4–3.5 Ga microbial biomarkers in pillow lavas and hyaloclastites from the Barberton Greenstone Belt, South Arica. Earth Planet Sci Lett. 2006;241(3-4):707–722.
    1. Banerjee NR, et al. Direct dating of Archean microbial ichnofossils. Geology. 2007;35(6):487–490.

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