Tracking the Deep Biosphere through Time

Henrik Drake,Christine Heim,Magnus Ivarsson

doi:10.3390/geosciences10110461

Henrik Drake, Christine Heim + Show 1 more

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https://doi.org/10.3390/geosciences10110461

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Abstract

The oceanic and continental lithosphere constitutes Earth’s largest microbial habitat, yet it is scarcely investigated and not well understood. The physical and chemical properties here are distinctly different from the overlaying soils and the hydrosphere, which greatly impact the microbial communities and associated geobiological and geochemical processes. Fluid–rock interactions are key processes for microbial colonization and persistence in a nutrient-poor and extreme environment. Investigations during recent years have spotted microbial processes, stable isotope variations, and species that are unique to the subsurface crust. Recent advances in geochronology have enabled the direct dating of minerals formed in response to microbial activity, which in turn have led to an increased understanding of the evolution of the deep biosphere in (deep) time. Similarly, the preservation of isotopic signatures, as well as organic compounds within fossilized micro-colonies or related mineral assemblages in voids, cements, and fractures/veins in the upper crust, provides an archive that can be tapped for knowledge about ancient microbial activity, including both prokaryotic and eukaryotic life. This knowledge sheds light on how lifeforms have evolved in the energy-poor subsurface, but also contributes to the understanding of the boundaries of life on Earth, of early life when the surface was not habitable, and of the preservation of signatures of ancient life, which may have astrobiological implications. The Special Issue “Tracking the Deep Biosphere through Time” presents a collection of scientific contributions that provide a sample of forefront research in this field. The contributions involve a range of case studies of deep ancient life in continental and oceanic settings, of microbial diversity in sub-seafloor environments, of isolation of calcifying bacteria as well as reviews of clay mineralization of fungal biofilms and of the carbon isotope records of the deep biosphere.

Highlights

The deep biosphere is estimated to represent a significant portion of all live biomass on Earth [1,2]
The results show that the combined high spatial-resolution stable isotope and geochronology approach is suitable for characterizing paleo-fluid flow in micro-karst in nappe units
Sallstedt et al [38] review the current data on clay mineralization by fossil fungal biofilms from oceanic and continental subsurface igneous rock

Summary

Introduction

The deep biosphere is estimated to represent a significant portion of all live biomass on Earth [1,2]. The microbial communities here include mainly prokaryotes (bacteria and archaea) [6] but findings of eukaryotes such as active and fossilized fungi [7,8,9,10,11,12,13,14,15], as well as live and indigenous nematodes [16], have been reported at great depth. The deep biosphere is the second largest reservoir of live biomass today, only surpassed by land plants. It has been put forward that most of Earth’s live biomass (~80%) was to be found in the deep biosphere prior to plant colonization of land [23]. The contributions range from detection of ancient biosignatures in continental and oceanic settings, to microbial diversity in sub-seafloor environments and to isolation of calcifying bacteria. Two articles timely review clay mineral fossilization of fungal biofilms and the carbon isotope records of the deep biosphere

An Overview of the Special Issue and the Contributions

Summary and Outlook