Ideas and perspectives: hydrothermally driven redistribution and sequestration of early Archaean biomass – the “hydrothermal pump hypothesis”

Abstract

Abstract. Archaean hydrothermal chert veins commonly contain abundant organic carbon of uncertain origin (abiotic vs. biotic). In this study, we analysed kerogen contained in a hydrothermal chert vein from the ca. 3.5 Ga Dresser Formation (Pilbara Craton, Western Australia). Catalytic hydropyrolysis (HyPy) of this kerogen yielded n-alkanes up to n-C22, with a sharp decrease in abundance beyond n-C18. This distribution (≤ n-C18) is very similar to that observed in HyPy products of recent bacterial biomass, which was used as reference material, whereas it differs markedly from the unimodal distribution of abiotic compounds experimentally formed via Fischer–Tropsch-type synthesis. We therefore propose that the organic matter in the Archaean chert veins has a primarily microbial origin. The microbially derived organic matter accumulated in anoxic aquatic (surface and/or subsurface) environments and was then assimilated, redistributed and sequestered by the hydrothermal fluids (“hydrothermal pump hypothesis”).

Organic signatures in Pleistocene cherts from Lake Magadi (Kenya), analogs for early Earth hydrothermal deposits

“…Our experiments were conducted with a HyPy device from Strata Technology Ltd. (Nottingham, UK), following existing protocols (e.g., Brocks et al, 2003b;Marshall et al, 2007;Duda et al, 2018). In brief, between 1-10 mg of pre-extracted kerogen (3x ultrasonically extracted in DCM/MeOH (3/1, v/v)) was loaded with 10 wt.% of the catalyst and then pyrolyzed under a constant hydrogen flow of 6 L min −1 .…”

“…A fraction of the organic matter preserved in the Magadi cherts may have been introduced by hydrothermal fluids. Such hydrothermally driven redistribution of organic matter has recently been proposed as an important process for kerogen in Archean hydrothermal vein cherts ("hydrothermal pump hypothesis"; Duda et al, 2018). Another similar feature to findings from Archean cherts is the variability of organic matter characteristics on a small spatial scale observed in the Lake Magadi samples (i.e., heterogeneous thermal maturities of organic matter within a given sample; appearance of organic matter in clots, layers or carbonate rhombs; see Ueno et al, 2004;Allwood et al, 2006;Tice & Lowe, 2006;Glikson et al, 2008; Biogeosciences Discuss., https://doi.org/10.5194/bg-2018-513 Manuscript under review for journal Biogeosciences Discussion started: 2 January 2019 c Author(s) 2019.…”

“…Our results highlight the possibility that organic matter of very different nature and maturity may be enclosed into hydrothermal chert precipitates a priori. Such in-situ mixing of different organic components should also be considered in the interpretation of Archean environments (see Allwood et al, 2006;Glikson et al, 2008;Morag et al, 2016;Duda et al, 2018). Of course, the heterogeneous maturity signals still have to be in accordance with the overall metamorphic history of the host rock.…”

Investigating the Effect of Perchlorate on Flight-like Gas Chromatography–Mass Spectrometry as Performed by MOMA on board the ExoMars 2020 Rover

“…Organic matter trapped in opaline silica has a high preservation potential (as e.g., shown for Archean cherts) and is thus a highpriority astrobiology target for the ExoMars 2020 mission MIßBACH ET AL. (Marshall et al, 2007;Westall et al, 2015;Duda et al, 2016Duda et al, , 2018. Before analysis, the rock pieces were manually powdered with a mortar that had been intensively rinsed with isopropanol and dried prior to use.…”

Habitability of the early Earth: Liquid water under a faint young Sun facilitated by strong tidal heating due to a nearby Moon

“…1 shows the 3.49 Ga North Star Basalt in the Pilbara region (Western Australia), which has pillow structures (Hickman, 1977) and thus evidently formed in aquatic environments. The North Star Basalt and other Paleoarchean pillowed basalts in this area (e.g., Mount Ada Basalt, Apex Basalt, Euro Basalt) are typically crosscut by numerous chert veins, which record hydrothermal pumping of surface water through early Earths crust ("hydrothermal pump hypothesis"; Duda et al, 2018).…”