Biotic Enhancement of Weathering over the Past 3.7 Billion Years

Gregory J. Retallack

Dept. of Earth Sciences, University of Oregon, Eugene, Oregon 97403-1272, USA, gregr@uoregon.edu

Abstract

Over the past four billion years, our sun became 30% brighter, yet Earth’s water has neither completely frozen nor boiled off during that time. A theoretical solution to this paradox is a carbon dioxide greenhouse planetary thermostat regulated by evolutionary advances in biologically mediated silicate and apatite weathering. This carbon sequestration history can now be quantified using paleosols. Calculations of precipitation-normalized nutrient depletion rates (µmol mm^–1 a^–1) in paleosols ranging in age back to 3.7 Ga show discrete order of magnitude increases in carbon consumption by silicate and apatite weathering due to evolutionary advances in life on land at around the Great Oxidation Event (2.45 Ga) and Neoproterozoic Oxidation Event (0.8 Ga). This biological weathering countered increased solar luminosity and continued emission of volcanic greenhouse gases.

Manuscript received 15 Apr. 2022. Revised manuscript received 10 June 2022. Manuscript accepted 17 June 2022. Posted 14 July 2022.

© The Geological Society of America, 2022. CC-BY-NC.

https://doi.org/10.1130/GSATG543A.1