The disputed whiff of oxygen
Metals in Australian shale suggested oxygen arrived early — until the rock's history was re-examined.
- When
- Known to
- ± 30 million years
- Era
- Paleoproterozoic, Proterozoic
Molybdenum and sulfur enrichments in the ~2.5-billion-year-old Mount McRae Shale were read as a transient pulse of oxygen some 50 million years before the Great Oxidation Event, and became the textbook example of an early whiff. A detailed reappraisal found the metals sit with late-stage pyrite rather than original organic carbon, implying they were added long after deposition. The original authors dispute the reinterpretation. Whether oxygen genuinely appeared this early is unresolved.