Thermochronologic perspectives on the deep-time evolution of the deep biosphere

Abstract

The Earth’s deep biosphere hosts some of its most ancient chemolithotrophic lineages. The history of habitation in this environment is thus of interest for understanding the origin and evolution of life. The oldest rocks on Earth, formed about 4 billion years ago, are in continental cratons that have experienced complex histories due to burial and exhumation. Isolated fracture-hosted fluids in these cratons may have residence times older than a billion years, but understanding the history of their microbial communities requires assessing the evolution of habitable conditions. Here, we present a thermochronological perspective on the habitability of Precambrian cratons through time. We show that rocks now in the upper few kilometers of cratons have been uninhabitable (>∼122 °C) for most of their lifetime or have experienced high-temperature episodes, such that the longest record of habitability does not stretch much beyond a billion years. In several cratons, habitable conditions date back only 50 to 300 million years, in agreement with dated biosignatures. The thermochronologic approach outlined here provides context for prospecting and interpreting the little-explored geologic record of the deep biosphere of Earth’s cratons, when and where microbial communities may have thrived, and candidate areas for the oldest records of chemolithotrophic microbes.

Physicochemical Conditions of the Devonian-Jurassic Continental Deep Biosphere Tracked by Carbonate Clumped Isotope Temperatures of Granite-Hosted Carbonate Veins

“…The T-Δ 47 are above regional sea surface temperatures estimates from δ 18 O VPDB in conodont apatite and brachiopods from the Eifelian to early Famennian (22 to 32 °C, 6 Geofluids [45]. This confirms that brine must have circulated below the thick sedimentary successions at burial depths, which is consistent with the temperature constraints on exhumation histories from the earlier study [23]. The second group of data shows lower T-Δ 47 (51 ± 5 to 65 ± 2 °C) and lower δ 18 O fluid VSMOW value (−0:9 ± 0:6 to −6:7 ± 1:9‰ VSMOW), corresponding to samples dominated by the later generation (younger than ~260 Ma) of calcite [22].…”

“…Sample "KLX 14A 80" yields an Rb-Sr (isochrones of calcite-K-rich clay mineral pairs) age of 393 ± 15 Ma [22]. During this period, the fracture approached the surface through exhumation, and extension was prevalent [23]. At all sites, an early period of Proterozoic precipitation of a high-temperature mineral assemblage, which includes epidote, was followed by a Mesoproterozoic period of hydrothermal precipitation of different, lower temperature minerals, including adularia (older generation), hematite, prehnite, and calcite, followed by several pulses of abundant Phanerozoic precipitation of calcite, pyrite, adularia, clay minerals, and quartz in veins [20].…”

Origin and Evolution of Pseudomurein Biosynthetic Gene Clusters

“…There are also Archean rocks from up to 3.5 Gy containing chemical traces of microbial methanogenesis and sulfate reduction (Shen et al 2001; Ueno et al 2006; Aoyama and Ueno 2018; Catling and Zahnle 2020; Mißbach et al 2021), thereby indicating that methanogenesis could be one of the most ancient biochemical pathways. Moreover, methanogenesis is a metabolism specific to the archaeal lineage (Gribaldo et al 2006; Sorokin et al 2017; Spang and Ettema 2017; Drake and Reiners 2021). Regarding bacterial microfossils, only three are unambiguously identified, all affiliated with the cyanobacterial lineage, of which Eoentophysalis , the oldest one, has been described from 1.9 Gy stromatolites (Hofmann 1976).…”

“…Moreover, methanogenesis is a metabolism specific to the archaeal lineage (Gribaldo et al 2006;Sorokin et al 2017;Spang and Ettema 2017;Drake and Reiners 2021). Regarding bacterial microfossils, only three are unambiguously identified, all affiliated with the cyanobacterial lineage, of which Eoentophysalis, the oldest one, has been described from 1.9 Gy stromatolites (Hofmann 1976).…”

The Low Permeability of the Earth’s Precambrian Crust

“…In sedimentary environments, permeabilities generally decrease from the ground surface to depths of several km due to compaction and diagenesis 19,34 but a similar trend is not obvious in Precambrian rock below 1 km. Any trends related to geomechanical and geochemical processes that are a simple function of depth could be overwhelmed by the long and often complex burial and exhumation histories of Precambrian rocks 35 . The apparent increase in permeability from Canada to Fennoscandia to South Africa hint at the importance of differences in the geological histories of these settings that promise to be important issues for future studies.…”