Despite bearing witness to its own increase in Earth's atmosphere by around 2.5 to 2.3 billion years ago, oxygen has had relatively little to say about its own early history until now.
A recent EU-funded study provides a fresh perspective on one of Earth history's most significant stories — the rise of oxygen.
While the recent history of Earth's atmosphere can be accessed by directly measuring atmospheric gases trapped in ice cores, it may be surprising to know that a similarly faithful time capsule of atmospheric oxygen is not yet known for the majority of Earth history. The rise of atmospheric oxygen is one of Earth history's greatest stories but this story is typically told through secondhand evidence, such as from proxies of sulfur stable isotope evidence from ancient rocks.
Stable isotopes of sulfur are particularly helpful for understanding the time when oxygen first accumulated in Earth's atmosphere because they show a characteristic response to the increase in oxygen above 0.001% of today's atmospheric levels. However, the record of how the sulfur isotope record in rocks responds to the first increases in atmospheric oxygen does not have a completely straightforward interpretation. Competition between global versus local, and original versus secondary, processes influence the preservation of chemical signals in ancient rocks. Accordingly, additional evidence is needed to support current interpretations of early atmospheric oxygen that are based on different proxies.
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