Neoproterozoic oxygenation event

Unlike the GOE, it is unclear whether the NOE was a synchronous, global event or a series of asynchronous, regional oxygenation intervals with unrelated causes.

These elevated δ13C values are believed to be linked to an evolutionary radiation of eukaryotic plankton and enhanced organic burial, which in turn indicate a spike in oxygen production during this interval.

[2] δ15N data from 750 to 580 million year-old marine sediments hailing from four different Neoproterozoic basins show similar nitrogen isotope ratios to modern oceans, with a mode of +4% and a range from -4% to +11%.

No significant change is observed across the Cryogenian-Ediacaran boundary, implying that oxygen was already ubiquitous in the global ocean as early as 750 Mya, during the Tonian period.

[6] Seawater sulfate δ34S values, which saw a gradual increase over most of the Neoproterozoic punctuated by major drops during glaciations,[7] show a significant positive excursion during the Ediacaran, with a corresponding decrease in pyritic δ34S.

Banded iron formations (BIFs) deposited during the Neoproterozoic consistently display highly positive δ53Cr values, from 0.9% to 4.9%, demonstrating the era's oxygenation of the atmosphere.

[17] During the Boring Billion, open ocean productivity was very low compared to the Neoproterozoic and Phanerozoic as a result of the absence of planktonic nitrogen-fixing bacteria.

The evolution and radiation of nitrogen-fixing bacteria and non-nitrogen-fixing picocyanobacteria capable of occupying marine planktonic niches and consequent changes to the nitrogen cycle during the Cryogenian are believed to be a culprit behind the rapid oxygenation of and removal of carbon dioxide from the atmosphere, which also helps explain the development of extremely severe glaciations that characterised this period of the Neoproterozoic.

O 2 build-up in the Earth's atmosphere . Red and green lines represent the range of the estimates while time is measured in billions of years ago (Ga).
  • Stage 1 (3.85–2.45 Ga): Practically no O 2 in the atmosphere. The oceans were also largely anoxic – with the possible exception of O 2 in the shallow oceans.
  • Stage 2 (2.45–1.85 Ga): O 2 produced, rising to values of 0.02 and 0.04 atm, but absorbed in oceans and seabed rock. (Great Oxidation Event)
  • Stage 3 (1.85–0.85 Ga): O 2 starts to gas out of the oceans, but is absorbed by land surfaces. No significant change in oxygen level.
  • Stages 4 and 5 (0.85 Ga – present): Other O 2 reservoirs filled; gas accumulates in atmosphere. [ 1 ] Stage 4 is known as the neoproterozoic oxygenation event.