Abstract
The diversification of complex animal life during the Cambrian Period (541–485.4 Ma) is thought to have been contingent on an oxygenation event sometime during ~850 to 541 Ma in the Neoproterozoic Era. Whilst abundant geochemical evidence indicates repeated intervals of ocean oxygenation during this time, the timing and magnitude of any changes in atmospheric pO2 remain uncertain. Recent work indicates a large increase in the tectonic CO2 degassing rate between the Neoproterozoic and Paleozoic Eras. We use a biogeochemical model to show that this increase in the total carbon and sulphur throughput of the Earth system increased the rate of organic carbon and pyrite sulphur burial and hence atmospheric pO2. Modelled atmospheric pO2 increases by ~50% during the Ediacaran Period (635–541 Ma), reaching ~0.25 of the present atmospheric level (PAL), broadly consistent with the estimated pO2 > 0.1–0.25 PAL requirement of large, mobile and predatory animals during the Cambrian explosion.
Highlights
The diversification of complex animal life during the Cambrian Period (541–485.4 Ma) is thought to have been contingent on an oxygenation event sometime during ~850 to 541 Ma in the Neoproterozoic Era
The oxygenation of the Earth system was a necessary condition for the rise of complex animal life[1,2,3,4,5], which occurred in several steps[6,7,8]
The Great Oxidation Event (GOE) ~2.3 Ga saw a permanent rise in atmospheric oxygen from 9
Summary
The diversification of complex animal life during the Cambrian Period (541–485.4 Ma) is thought to have been contingent on an oxygenation event sometime during ~850 to 541 Ma in the Neoproterozoic Era. The redox state of the ocean clearly fluctuated, with a series of transient oxygenation events (Fig. 1c) getting somewhat more frequent through the Ediacaran and early-mid Cambrian[16] These include partial and temporary oxygenation of deeper waters following the Sturtian22 ~660 Ma, Marinoan23 ~635 Ma and Gaskiers24,25 ~580 Ma glaciations. Assuming that global arc magmatism is proportional to subduction, mantle depletion curves point to a maximum in subduction during the early Phanerozoic[36], supported by reconstructions of subduction-zone lengths from both plate-tectonic reconstructions[37] and kinematic modelling[38] Whilst these methods all carry uncertainties, the geologic data all point to a general step-increase in subductiondriven degassing across the Proterozoic-Phanerozoic transition
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