254 / 2025-04-15 21:48:24

Rethinking Microbialites in Extinction Events: Geochemical Modelling of Biomineralization in Extinctions

Microbialites,Extinction,Carbon Cycle

Theme 4: Microbial and Biogeochemical Evolution through Time > Session 4b: Roles of Microbes in Shaping Our Habitable Earth

Abstract: Microbes function as the engine in ocean carbon cycles. Through bio-induced mineralization and bio-controlled mineralization, microbes affect carbonate precipitation in the ocean, hence controlling dissolved carbon in the ocean and the carbon cycle. Microbial reef or microbialite occupies a unique ecological niche in the evolution of carbonate mineralization. In phanerozoic, microbialite often resurges after mass extinctions, which has been consistently observed across several extinction boundaries, especially the end-Ordovician, end-Devonian, end-Permian, and end-Triassic. The flourishing of microbialite can be attributed to several reasons. Firstly, mass extinctions severely reduced metazoan diversity, significantly reducing grazing pressure and giving microbial mats a chance to thrive and lithify. Secondly, post-extinction settings offer niches that are rapidly occupied by "disaster taxa" like microbialites. Here, we emphasize that the resurge of microbialite is correlated with and responds to the elevation of carbonate saturation in seawater caused by metazoan decline. Drop in metazoan skeleton reduces biocalcification and elevates carbonate saturation, allowing microbes to be mineralized to form microbialite. In turn, microbe mineralization maintains high saturation in seawater and, therefore, sustains high pCO₂ level after extinction. In this study, we use a geochemical model to modify seawater carbon cycle change with the emergence of microbes. We propose that microbes not only are passively involved but also profoundly participate in the shift of the carbon cycle in geological times.