Possible link between Earth’s rotation rate and oxygenation
The biotic and abiotic controls on major shifts in atmospheric oxygen and the persistence of low-oxygen periods over a majority of Earth’s history remain under debate. Explanations of Earth’s stepwise pattern of oxygenation have mostly neglected the effect of changing diel illumination dynamics linked to daylength, which has increased through geological time due to Earth’s rotational deceleration caused by tidal friction. Here we used microsensor measurements and dynamic modelling of interfacial solute fluxes in cyanobacterial mats to investigate the effect of changing daylength on Precambrian benthic ecosystems. Simulated increases in daylength across Earth’s historical range boosted the diel benthic oxygen export, even when the gross photosynthetic production remained constant. This fundamental relationship between net productivity and daylength emerges from the interaction of diffusive mass transfer and diel illumination dynamics, and is amplified by metabolic regulation and microbial behaviour. We found that the resultant daylength-driven surplus organic carbon burial could have shaped the increase in atmospheric oxygen that occurred during the Great and Neoproterozoic Oxidation Events. Our suggested mechanism, which links the coinciding increases in daylength and atmospheric oxygen via enhanced net productivity, reveals a possible contribution of planetary mechanics to the evolution of Earth’s biology and geochemistry.
The rise of free oxygen (O2) in the Earth’s atmosphere and oceans enabled the evolution of aerobic life1. Oxygenic photosynthesis (OP) in microbial mats was a substantial source of O2 for the Great Oxidation Event (GOE) ~2.4 billion years ago (Ga), during the stable low-O2 conditions that followed and for the Neoproterozoic Oxygenation Event (NOE) ~600 Ma (ref. 2). The biological3,4, tectonic5 and geochemical6,7 mechanisms that determined this stepwise pattern of oxygenation are still debated. Here we explore a previously unconsidered link between Earth’s oxygenation pattern and rotation rate, which decelerated over geological time due to tidal friction8,9. We establish a mechanistic link between daylength and export fluxes of solutes from microbial mats. Experimental measurements and models of Proterozoic cyanobacterial mat analogues show that longer daylength increases benthic O2 export, changes the balance between aerobic and anaerobic remineralization, and thus enhances the diel organic carbon (Corg) burial. We then investigated the remarkable similarity between the timing and pattern of increase in atmospheric O2 (\(p{{\rm{O}}_2}\) as a fraction of the present atmospheric level (PAL)) and daylength. We found that increases in daylength could plausibly have influenced Earth’s oxygenation, particularly around key oxidation events, and thus helped to pave the way for the evolution of plants and animals of the modern world.
