Theoretical origin of life: early living filament fossils (Introduction)

by David Turell , Friday, July 16, 2021, 21:42 (1226 days ago) @ David Turell

From 3.42 byo:

https://advances.sciencemag.org/content/7/29/eabf3963?utm_campaign=toc_advances_2021-07...

"Abstract
Subsurface habitats on Earth host an extensive extant biosphere and likely provided one of Earth’s earliest microbial habitats. Although the site of life’s emergence continues to be debated, evidence of early life provides insights into its early evolution and metabolic affinity. Here, we present the discovery of exceptionally well-preserved, ~3.42-billion-year-old putative filamentous microfossils that inhabited a paleo-subseafloor hydrothermal vein system of the Barberton greenstone belt in South Africa. The filaments colonized the walls of conduits created by low-temperature hydrothermal fluid. Combined with their morphological and chemical characteristics as investigated over a range of scales, they can be considered the oldest methanogens and/or methanotrophs that thrived in an ultramafic volcanic substrate.

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"The filaments satisfy the commonly accepted biogenicity, indigenicity, and syngenicity criteria. The studied filaments also differ from known abiotic pseudofossils in the specific combination of their site of occurrence, 3D morphological complexity, kerogenous nature, spectrally observed ultrastructures, and their specific metal-organic signature. Although biomorphs, produced in the absence of any direct biological activity under geochemical conditions that could have existed on early Earth, must be considered when evaluating the biogenicity of putative early trace of life, their features with the various attributes of the filaments described here are currently not known. Possibly the strongest evidence for the biogenicity of the studied filaments is their occurrence in specific associations (single or in clusters) within different parts of the vein microhabitat and in association with biofilms.

"Although cellular fossils of archaeal methanogens and methanotrophs have not yet been reported in the Paleoarchean record and Paleoarchean geochemical evidence (carbon isotopes) for microbially produced methane is limited, methane-utilizing metabolic pathways are commonly recognized as ancient in origin. Despite the demonstrated fossilization potential of Archaea, their fossil record is restricted to the Phanerozoic. Our findings could possibly extend this record back to 3.42 Ga.

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"In this work, a suite of converging and mutually supportive evidence indicative of biogenicity (morphology and chemical composition) and a favorable ecological setting along with meeting endogenicity and syngenicity criteria was established for filaments in a habitable Archean subsurface ultramafic environment. This discovery of microfossils extends knowledge of the early subsurface fossil record and provides a strong case for the importance of subsurface hydrothermal systems as an abode for early life. These findings provide the oldest direct evidence for subsurface methane-cycling microorganisms, most likely methanogens, consistent with their expected antiquity based on carbon isotope analysis of fluid inclusions and molecular evidence.

Comment: More evidence of an early start to life after Earth formed.