Mesoproterozoic Archives

Relationship between total group age T and crown group age tcg across various diversification rates λ − µ, equation 4. The heatmap represents the crown group age for a given rate and total group age (isolines are presented for reference). The orange dot-dashed line is the minimum value for T to fit the observed eukaryotic-grade fossil record of the late Palaeoproterozoic (1780 Ma), the red-dashed isoline is the minimum age for tcg fitting the observed crown-eukaryote fossil record from the end of the Mesoproterozoic (1050 Ma), and the grey interval is the range of possible tcg require to obtain the living diversity for a given rate and total age. The isolines for late LECA (tcg = 1200) or generous late LECA (tcg = 1400 Ma) are the red-dotted lines. -- biorxiv.org

Biosignatures & Paleobiology, Fossils & Paleontology, Genomics, Proteomics, Bioinformatics, Habitable Zones, Microbiology & Virology, Origin & Evolution of Life, Sample Return, Status Report

Clade Dynamics Support An Early Origin Of Crown Eukaryotes

by Keith CowingApril 7, 2026April 7, 2026

The timing of the last eukaryotic common ancestor (LECA) remains a fundamental question in evolutionary biology and palaeontology. Unambiguous eukaryotic-grade fossils appear from 1780 Ma, but no crown-group supergroups are […]

(A) Predicted pO2 (red line) and (B) pCO2 (purple line) values are compared for a range of possible assumed pN2. Vertical dashed lines and colored bands reflect pN2 estimates for 1.44 Ga. from existing models (22–26). For O2, the green and yellow bands reflect the thresholds for early animal respiration and full O3 shielding, respectively (31, 32). The pO2 safely exceeds these thresholds (0.01 PAL) if pN2 exceeded 0.2 bar. For CO2, horizontal dashed lines reflect estimated CO2 contents necessary to achieve the specified temperature (33–35). The diagonal line extrapolates from Archean atmospheric models that account for the effect of total atmospheric pressure on the required CO2 to keep the planet warm (35). Based on these points, our data suggests modern-like climates were possible if pN2 exceeded 0.5 bar. -- PNAS

Astrogeology, Atmospheres, Climate, Weather, Biogeochemical Cycles & Geobiology, Biosignatures & Paleobiology, Gaia - Planetary Perspectives, Status Report

Direct Constraints From 1.4 Ga Fluid Inclusions Reveal A Fair Climate And Oxygenated Atmosphere

by Keith CowingJanuary 8, 2026January 8, 2026

The Mesoproterozoic eon, often regarded as mundane and static, lays the foundation for dramatic transformations in Earth’s physical and biological evolution during the subsequent Neoproterozoic.