Biosignatures across Space and Time—Special Collection

The Centre for Geobiology at the University of Bergen together with the Nordic Network of Astrobiology hosted an international conference “Biosignatures across Space and Time” between May 20 and 22, 2014 (Fig. 1). Delegates from more than 19 countries attended the 3-day meeting, with presentations on different aspects of biosignatures in the early Archean rock record, at extreme terrestrial sites, and in potential extraterrestrial environments. Session themes and key topics at the meeting included the question of life beyond Earth, how many Earth-sized planets might exist in the Universe, and whether life had its origin at hydrothermal vents. The meeting also addressed the evidence for biosignatures and habitable environments on early Earth and what this could potentially say about habitability in the wet subsurface of Mars and other rocky planets. The Biosignatures across Space and Time meeting was aimed at bringing a wide cross section of astrobiologists together to tackle these big questions by doing big science.

OPEN IN VIEWER

FIG. 1.

Group photograph of all delegates at the Bergen astrobiology meeting Biosignatures Across Space and Time, hosted by the Centre for Geobiology and the Nordic Network of Astrobiology. (Photo credit: E. Grosch)

One of the scientific outcomes of the meeting is a special collection of papers, presented herein, that discusses different types of biosignatures (geochemical and textural) and related processes in various extreme environments on Earth, in the Solar System, and beyond. Sephton et al. propose that the first chemical steps toward life may be recorded as prebiotic organic matter in meteorites. They suggest that macromolecules in carbonaceous meteorites may have been derived from more than one source, one of which may have been from outside our early solar nebula. Watson and Sephton explore potential low-temperature catalysis reactions between Fe-rich clay minerals and organic molecules in meteorites as a mechanism for producing complex aromatic molecules.

In a terrestrial analog study, Türke et al. investigate low-temperature alteration of basaltic glass and the role of radioactive elements concentrated in palagonite in the radiolytic production of hydrogen as a microbial energy source. They postulate that hydrothermal alteration of martian basalt may have led to production of enough hydrogen to have once supported microbial life in the subsurface of early Mars.

Investigations of early Archean Earth environments and biosignatures include work by Konhauser et al., who discuss bioessential trace metals, such as nickel in Precambrian iron formations, and their importance to the ancient biosphere. In another contribution, Whitehouse et al. use Fe isotopes to explore 3.8-billion-year-old sedimentary environments and their relevance to the earliest contested traces of life preserved at Akilia in Greenland. In a hypothesis article, Grosch and Hazen postulate on the sites for the origin of life and the role of early subsurface microbial life in driving crustal evolution and biogeochemical environments on early Earth.

Two papers in this volume apply Raman spectroscopy to exploring potential biosignatures. Qu et al. apply Raman spectroscopy combined with Fourier transform infrared spectroscopy to organic matter in selected cherts to study their ultrastructural heterogeneity and to test biogenicity. In a separate study, Storme et al. use Raman spectroscopy to characterize the UV-protective pigment gloeocapsin with relevance to the survival of cyanobacteria.

The remaining three contributions focus on reliably identifying textural biosignatures and testing their biogenicity in different rock types. Campbell et al. study filaments and various microtextures in silicified hot-spring deposits with the aim of understanding their eventual preservation and identification in the geological record. Brasier et al. develop criteria for testing the biogenicity of filaments and stromatolite morphologies in freshwater carbonate deposits. Then McLoughlin and Grosch present a hypothesis article that provides a new hierarchical approach and practical guidelines to testing the biogenicity of microtextures in altered mafic-ultramafic terrestrial and extraterrestrial rocks.

The special issue on Biosignatures across Space and Time closes with a tribute to the late Professor Martin D. Brasier, who gave a presentation at the meeting on the earliest fossil evidence of life on Earth and who will be sadly missed by the Nordic Astrobiology meeting participants, colleagues, students, friends, and family.