ATMOSPHERE × EARTH × LIFE

The Neoproterozoic Oxygenation

~800 to 540 million years ago

Proterozoic · Neoproterozoic · Tonian

The Neoproterozoic Oxygenation is the second rise in oxygen in Earth's history, between 800 and 540 million years ago, a billion and a half years after the first rise.

The Neoproterozoic Oxygenation is a rise in oxygen named after the Neoproterozoic, the geological era in which it took place. It came a billion and a half years after a first rise and did not take the same form. Canfield and colleagues (2007) measured iron speciation in deep-sea sediments: the proportion of iron contained in minerals that form only without oxygen. In sediments laid down before and during the Gaskiers glaciation, an ice age 580 million years ago, this proportion indicates a deep ocean rich in iron and anoxic, that is, without oxygen. In sediments laid down after that glaciation, it indicates an oxygenated deep ocean. Stockey and colleagues (2024) analysed statistically the whole geochemical record, the chemical measurements made on ancient rocks. They found no evidence that the seas as a whole became oxygenated in the late Neoproterozoic. They did find a moderate, prolonged rise in atmospheric oxygen and in marine primary production, the organic matter that marine organisms make from light. Both changes would have raised dissolved oxygen and the food supply in shallow water, where the first animals lived.

Why it matters

Animal life consumes much oxygen and food: muscle, movement and predation use both, and other organisms had first to produce them. During this rise, oxygen and food increased together and gradually. This is why animals appear across tens of millions of years rather than on a single date.

Dating & uncertaintyDisputed

Researchers accept that oxygen rose a second time. They disagree on the magnitude, the rate and the date of the rise. Iron speciation shows a deep ocean that became oxygenated after the Gaskiers glaciation, 580 million years ago. Statistical analyses of the whole geochemical record find only a moderate, long-term rise. In these analyses, modern conditions are reached only in the Late Palaeozoic, the end of the era that follows the Neoproterozoic, well after the first animals.

Earth history as one day

19:46:154 h 14 min before midnight

if Earth’s 4.54 billion years were compressed into a single day