Canfield ocean

In a paper published in 1998 in Nature,[1] Canfield argued that the deep ocean was anoxic and sulfidic (also known as euxinic) during the time of the Boring Billion (1.8–0.8 billion years ago (Gya)), and that those conditions ceased the mineral deposition of iron-rich banded iron formations (BIF) in ocean sediments.

However, the atmosphere had enough oxygen to facilitate weathering of sulfate-containing terrestrial minerals, delivering sulfate (SO42-) to the ocean through runoff.

[1] Most evidence for euxinic ocean conditions comes from stable isotope ratios found in sediment records.

[4] A δ34S value higher than 45‰ would be evidence of a fully oxygenated ocean, while a δ34S value lower than 5‰ would imply an anoxic atmosphere.

This would prevent the high rates of primary production that are required for euxinic oceans to form in the first place.