Paleoproterozoic Archives - Astrobiology

PIXL micro-XRF observation from the third “Apollo Temple” scan (a,b), alongside a SHERLOC WATSON color image for context (c). An RGB composite shows the areas with relative enrichment of FeOT, SO3, and SiO2 where brownish tones highlight Fe-sulfide (a). Zones of Ni enrichment are seen in yellow (b) and marked with white arrows (a,b,c). Dashed black box shows the approximate area of the PIXL scan (c). Image Credit: NASA/JPL-Caltech.

Astrogeology, Atmospheres, Climate, Weather, Biogeochemical Cycles & Geobiology, Biosignatures & Paleobiology, Habitable Zones, Imaging & Spectroscopy, Mars, Robotics/Rovers/UAVs, Status Report

Strong Nickel Enrichment Co-located With Redox-organic Interactions In Neretva Vallis, Mars

by Keith CowingApril 8, 2026April 8, 2026

In 2024, NASA’s Perseverance rover explored Neretva Vallis, an ancient river channel that once transported water into Jezero crater.

Iron disruption through endosymbiosis: An overview of disruptive effects of iron throughout endosymbiosis, from ecological associations and biochemistries of archaea and bacteria (69) to LECA (90, 94). These effects may underlie a mechanistic connection between the cessation of marine iron deposition and the radiation of the earliest eukaryotes. -- biorxiv.org

Biogeochemical Cycles & Geobiology, Biophysics, Biosignatures & Paleobiology, Origin & Evolution of Life, Status Report

Did Iron Suppress Eukaryote Emergence and Early Radiation?

by Keith CowingFebruary 5, 2026June 11, 2026

The last eukaryotic common ancestor (LECA) is widely thought to have been an oxygen-respiring organism, arising through endosymbiosis when a free-living bacterium became the mitochondrion.

Conceptual model for the evolution of exoenzymes and the recycling of organic matter across the Great Oxidation Event (GOE). (A) In the Archean Ocean, prior to the GOE, the recycling of organic matter depended entirely on the activity of fermenters. This resulted in low recycling efficiency, elevated carbon burial, and limited regeneration of essential nutrients back into seawater. This scarcity of particulate organic matter (POM) also reduced the availability of niches for microbial colonization, thus limiting the selective pressure for the evolution of exoenzyme systems. (b) Following the GOE, rising oxygen levels increased the availability of high-energy electron acceptors (e.g. O2, nitrate and ferric iron), supporting the expansion of metabolic groups with high exoenzyme capacity, such as aerobic heterotrophs, dissimilatory nitrate reducers and dissimilatory ferric iron reducers. Concurrently, increases in POM abundance and microbial cell densities would have amplified the selective pressure to produce exoenzymes. Collectively, these changes in the Paleoproterozoic promoted more efficient recycling of organic matter and regeneration of nutrients back into the water column, ultimately fueling greater primary productivity and oxygen release. This feedback between exoenzyme evolution, nutrient cycling, and oxygen production would have amplified Earth’s progressive oxygenation. -- biorxiv.org

Atmospheres, Climate, Weather, Biochemistry & Organic Chemistry, Biogeochemical Cycles & Geobiology, Biophysics, Biosignatures & Paleobiology, Gaia - Planetary Perspectives, Origin & Evolution of Life, Status Report, Water/Hycean Worlds & Oceanography

Microbial Exoenzymes Catalyzed The Transition To An Oxygenated Earth

by Keith CowingOctober 11, 2025October 11, 2025

Microbial exoenzymes—extracellular enzymes secreted to degrade complex organic polymers— are essential for recycling carbon and nutrients, thus sustaining primary productivity in today’s oceans.

Biochemical requirements and toxicities for oxygen, iron and sulfide restrict conditions for endosymbiosis: Iron, sulfide and oxygen readily react with one another, leading to reservoir fluctuations that characterize Paleoproterozoic marine chemistry. A narrower set of interactive conditions involving these three chemicals (dotted box) are circumscribed by the context of cellular homeostatic constraints, which differ among organisms. Iron is biphasic: it is essential at lower cellular concentrations but toxic at higher cellular concentrations. Iron and oxygen homeostatic constraints must have been operable within archaea and bacteria across the process of endosymbiosis, up to and including full endogenization of the mitochondrion into a eukaryotic organelle. -- biorxiv.org

Biosignatures & Paleobiology, Genomics, Proteomics, Bioinformatics, Microbiology & Virology, Origin & Evolution of Life, Status Report

Did Iron Suppress Eukaryote Emergence and Early Radiation?

by Keith CowingJune 29, 2025June 28, 2025

The last eukaryotic common ancestor (LECA) is widely thought to have been an oxygen-respiring organism, arising through endosymbiosis when a free-living bacterium became the mitochondrion.

Photo Credit DALL-E, prompt by Harrison Tasoff. A soft summer evening in the Paleoproterozoic, as envisioned by DALL-E.

Away Teams & Field Reports, Biosignatures & Paleobiology, Fossils & Paleontology, Microbiology & Virology, Origin & Evolution of Life, Press Release

Even The Oldest Eukaryote Fossils Show Dazzling Diversity And Complexity

by Keith CowingJanuary 30, 2024January 30, 2024

The sun has just set on a quiet mudflat in Australia’s Northern Territory; it’ll set again in another 19 hours. A young moon looms large over the desolate landscape. No […]

TL photomicrograph of a five-celled filament with constant width and dark narrow transverse bands. -- Science Advances

Biosignatures & Paleobiology, Fossils & Paleontology, Microbiology & Virology, Origin & Evolution of Life, Press Release

North China Fossils Show Eukaryotes First Acquired Multicellularity 1.63 Billion Years Ago

by Keith CowingJanuary 25, 2024January 24, 2024

In a study published in Science Advances on Jan. 24, researchers led by Prof. ZHU Maoyan from the Nanjing Institute of Geology and Palaeontology of the Chinese Academy of Sciences […]