Tracking the Deep Biosphere through Time

Dear Colleagues,

The oceanic and continental lithosphere constitutes Earth´s largest microbial habitat, yet it is poorly investigated and not well understood. Its physical and chemical properties are distinctly different from the overlaying soils and the hydrosphere, which greatly impacts the microbial communities and associated geobiological and geochemical processes. Fluid-rock interactions, i.e., the serpentinization of ultramafic rocks and the subsequent production of gases and molecular species, are key processes for microbial colonization and persistence in a nutrient-poor and extreme environment. Investigations during recent years have indicated microorganism-related 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 increasing understanding of the evolution of the deep biosphere in (deep) time. Similarly, the preservation of isotopic signatures as well as organic compounds within fossilized microcolonies or related mineral assemblages in voids, cements, and fractures/veins in the upper crust provide 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 Earth life at times when the surface was inhabitible, and of the preservation of signatures of ancient life, which may have astrobiological implications.

This Special Issue seeks to cover all geobiological aspects of the upper crust (continental and marine) and we invite contributions with relevance to geomicrobiology, isotope geochemistry, microbial-activity-associated geochronology and related geochemical and hydrochemical proxies as well as presentations on new methods, techniques, and experimental approaches in both the modern and ancient crust. We wish to cover a broad spectrum of environments such as ultra-mafic, mafic, and felsic systems, as well as hydrothermal/geothermal areas and sedimentary successions. We encourage contributions related to scientific drilling programs as well as research from underground facilites and deep drillings related to mining activity or nuclear waste disposal, in addition to studies of exposed ancient crust. Astrobiological implications are also encouraged.

Dr. Henrik Drake
Dr. Magnus Ivarsson
Dr. Christine Heim
Guest Editors

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