Phanerozoic atmosphere oxygen cycles revealed by trace elements in marine pyrite

TL;DRAbstract

It is generally accepted that oxygen in the atmosphere rose in two major steps at s.round 2.4-2.2 and 0.7-0.5 billion years ago. The variation in atmosphere oxygen over the last 500 millionyears, is considered to have been relatively minor by comparison. Sedimentary pyrite from marine shales efficiently captures many trace elements from the oceans, providing a novel proxy forseawater chemistry. Here we use temporal changes in the selenium and cobalt content of Phanerozoic marine pyrite, coupled with the 87Sr/86Sr ratio in marine carbonate, to argue for fivedramatic p02 cycles, each starting with a period of oxygenation, followed by a period of de-oxygenation. The selenium proxy is based on the premise that increased erosion of continentalrocks leads to the release of selenium as both the selenate and selenite species. Under neutral to alkaline, oxygenated conditions the selenate species remains highly soluble, where it can bereadily transported via river systems to the ocean. Cobalt on

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