Hydrothermal activity, triggered by endogenic processes, distributes and redistributes organic matter through diffuse flow networks and may lead to a production of organic matter via abiotic synthesis. Today, hydrothermal seepage, especially at seafloor spreading zones, induces oases for diverse microbial communities in otherwise relatively hostile environments. Furthermore, hydrothermal fluids can deliver organic molecules as building blocks and/or substrates for primeval microorganisms and thus probably played a central role in the emergence of life on Earth. In this talk I will briefly outline evidence for traces of early life on Earth associated with hydrothermal processes from the 3.5 Ga old Dresser Formation (Pilbara, Western Australia). Recent findings strongly support the idea that microbial life in the Dresser Formation was linked to, and perhaps locally fuelled by, hydrothermal seepage. I will demonstrate that integrative study designs including analytical imaging techniques (e.g., Raman spectroscopy), biogeochemical approaches (e.g., catalytic hydropyrolysis and gas chromatography – mass spectrometry), stable isotope analysis and experimental approaches provide important insights into the complex interplay between biological and abiotic processes in early Archean hydrothermal habitats. Thus, they allow us to catch a glimpse into the earliest record of life on Earth.

Modern hydrothermal vents provide diverse environments for microorganisms. Here there is a large phylogenetic and physiological diversity of bacteria and archaea, occurring in a wide range habitats. An assumption is that similar communities of microorganisms have been present on Earth for an extremely long time, given that there is direct evidence of marine hydrothermal activity going back to the Archaean eon (which began 4 billion years ago), and the hypothesis that life may have originated in these environments. In this presentation I will review the fossil record of microorganisms at hydrothermal vents, focussing on volcanogenic massive sulfides (VMS), which formed at high temperature vents, and jaspers (iron-silica rocks), which formed at low-temperature, sulfide-poor vents. Occurrences of microorganisms in VMS go back to the Paleoarchean and in jaspers to the Eoarchaean (3.770, or possibly 4.280, billion years ago), with the latter being the possibly the oldest organisms yet discovered on Earth. These very early dates suggest that life may have been possible on Mars during its equivalent aged warmer period, and that life may be found at putative hydrothermal sites on the icy moons with liquid oceans (e.g. Europa and Enceladus).

The Moodies Group (~3.2 Ga) of the Barberton Greenstone Belt is one of the oldest and best-preserved shallow-water siliciclastic sequences. It also harbors one of the largest occurrences of Paleoarchean microbial mats and the oldest record of early Earth-Moon dynamics. The extent (ca. 40 km * 70 km), lithologic and alluvial-to-prodeltaic facies diversity (incl. paleosols, pedogenic concretions and microbial mats etc.) , good outcrop, and excellent preservation of Moodies strata allows the recognition of mappable systems tracts and sequence-stratigraphic surfaces. However, the lack of biostratigraphic constraints and the nonactualistic Archean surface conditions (absence of vegetation, aggressive chemical weathering, oceanic composition and temperatures, climate, tides) challenge the applicability of sequence-stratigraphic concepts. Well-studied Moodies strata north of the Inyoka Fault zone can be readily subdivided into several 3rd-order parasequence sets. Lower Moodies strata are characterized by an overall increase in accommodation space relative to sediment supply and comparative tectonic quiescence, whereas upper Moodies strata (above a basinwide volcanic unit) record an overfilled basin. Much less is known about the Moodies south of the Inyoka fault zone where the Masenjane Range exposes a section 600-2000 m thick of largely northeastward-prograding, coastal, deltaic and estuarine strata. They record at least five 4th-order shoaling-upward parasequences. Stacking patterns, paleocurrents and provenance indicators show an overall northeastward progradation of facies, likely controlled by local tectonothermal drivers, as evidenced by several syndepositional shallow sills, stockworks, and syndepositional normal faults. These may have been regionally related to the tightening and rotation of the Onverwacht Anticline and the formation of other paleogeographic features.

Geological evidence suggests liquid water on the earth's surface as early as 4.4 Ga when the faint young Sun only radiated about 70 % of its modern power output. At this point, Earth should have been a global snowball if it possessed atmospheric properties similar to those of modern Earth. An extreme atmospheric greenhouse effect, an initially more massive Sun, release of heat acquired during the accretion process of protoplanetary material, and radioactivity of early Earth material have been proposed as reservoirs or traps for heat. We explored the possibility that the new-born Moon, which formed about 69 Ma after the ignition of the Sun, generated extreme tidal friction - and therefore heat - in the Hadean and the Archean earth. We show that the Earth-Moon system has lost about 3 × 10^31 J (99 % of its initial mechanical energy budget) as tidal heat. Tidal heating of about 10 W/m^2 through the surface on a time scale of 100 Myr could have accounted for a temperature increase of up to 5 degrees Celsius on early Earth. Tidal heating alone does not solve the faint-young-sun paradox but it could have played a key role in combination with other effects. Future studies of the interplay of tidal heating, the evolution of the solar power output, and the atmospheric (greenhouse) effects on early Earth could help in solving the faint-young-sun paradox, particularly if tied to geologic evidence.
Details published in
Heller et al. (2021) accepted by Paläontologische Zeitung, PDF pre-print: https://arxiv.org/abs/2007.03423

The sole Archean data point to reconstruct past orbital parameters of the Earth’s moon is from the Moodies Group (ca. 3.22 Ga) of the Barberton Greenstone Belt. From time-series analysis of tidal bundles of a subaqueous sand wave, Eriksson and Simpson (2000) suggested that the Moon’s anomalistic month at 3.2 Ga was closer to 20 days than the present 27.5 days. This is in apparent accordance with models of orbital mechanics which place the Archean Moon in a closer orbit with a shorter period, resulting in stronger tidal action. Although our reexamination of the site confirmed that the sandstone bed in question is likely a subaqueous dune, mud clasts, channel-margin slumps, laterally aggrading channel fills and bidirectional paleocurrents suggest that this bedform was likely located in a major nearshore channel; it thus risks incompleteness. Remeasurements of foresets along the published traverse, perpendicular to bedding, failed to show consistent spectral peaks. Larger data sets acquired along additional traverses parallel to bedding along the 20.5 m-wide exposure are affected by zones of minor faulting, uneven outcrop weathering, changing illumination, weather, and observer bias. Our most robust measurements show a distinct periodicity peak of approximately 14, removed by Eriksson and Simpson (2000) in the original data, and are interpreted to be due to a lunar month of about 28 Earth days, as today. This estimate agrees well with Earth-Moon dynamic models which consider the conservation of angular momentum and place the Archaean Moon in a nearer orbit, rotating faster around a faster-spinning Earth.