The Deep Rocky Biosphere: New Geomicrobiological Insights and Prospects

Abstract

Rocks that react with liquid water are widespread but spatiotemporally limited throughout the solar system, except for Earth. Rock-forming minerals with high iron content and accessory minerals with high amounts of radioactive elements are essential to support rock-hosted microbial life by supplying organics, molecular hydrogen, and/or oxidants. Recent technological advances have broadened our understanding of the rocky biosphere, where microbial inhabitation appears to be difficult without nutrient and energy inputs from minerals. In particular, microbial proliferation in igneous rock basements has been revealed using innovative geomicrobiological techniques. These recent findings have dramatically changed our perspective on the nature and the extent of microbial life in the rocky biosphere, microbial interactions with minerals, and the influence of external factors on habitability. This study aimed to gather information from scientific and/or technological innovations, such as omics-based and single-cell level characterizations, targeting deep rocky habitats of organisms with minimal dependence on photosynthesis. By synthesizing pieces of rock-hosted life, we can explore the evo-phylogeny and ecophysiology of microbial life on Earth and the life’s potential on other planetary bodies.

Metagenome-derived virus-microbe ratios across ecosystems

“…Overall, our mVMR estimates across ecosystems question the currently widely held assumption that viruses outnumber cells at least by one order of magnitude. Even if ocean waters occupy an important fraction of Earth's volume, continental biomes together with the deep subsurface undoubtedly host most of the planet's biomass and cells [88,89].…”

The formation and stability of homochiral peptides in aqueous prebiological environment in the Earth's crust

“…A support for this hypothesis is the fact that the oldest signs of life, which are at least 3.5 billion years old, appear as fossilized microorganisms (bacteria) found in hydrothermal vent precipitates [25][26][27][28]. There are also direct measurements of a biosphere in the upper part of the wet crust, which today contains bacterias [29,30]. Here we argue for that the the location for prebiological self-assembly of homochiral peptides is a wet crust in the Hadean Eon.…”

“…Based on the latest literature regarding the conditions in the Earth's crust and upper part of the mantle there are several factors that point to, that the crust could be the location for the prebiological self-assembly of biomolecules, and there is nothing against it. The crust and the upper part of the mantle contains a substantial amount of water [16], and a substantial biomass and biodiversity [30], with an estimated number of (Prokaryotic) cells of the order 2 to 6×10 29 [73]. The crust and upper part of the mantle at the time prior to the emergence of life contained the necessary chemical substances for the synthesis of the biomolecules, and an aqueous environment in the crust beneath hydrothermal locations is a more likely place for the prebiological synthesis of peptides and carbohydrates and for the establishment of homochirality.…”

Origin of Homochirality: The Formation and Stability of Homochiral Peptides in Aqueous Prebiological Environment in the Earth’s Crust

“…Support for this hypothesis is the fact that the oldest signs of life, which are at least 3.5 billion years old, appear as fossilized microorganisms (bacteria) found in hydrothermal vent precipitates [25][26][27][28]. There are also direct measurements of a biosphere in the upper part of the wet crust, which today contains bacteria [29,30]. Here we argue that the location for prebiological self-assembly of homochiral peptides is a wet crust in the Hadean Eon.…”