Gas trapped in ancient bubbles reveals that Earth's atmosphere was rich in oxygen up to 200 million years earlier than models have predicted, well before animal diversity exploded.
Bubbles in salt crystals called halites (pictured) that formed millions of years ago can provide clues to ancient climates. Nigel Blamey of Brock University in St Catharines, Ontario, Canada, and his colleagues studied pockets of air inside 815-million-year-old halites from southwest Australia. The air contained nearly 11% oxygen, more than expected for that time period.
The authors suggest that high oxygen levels drove animal evolution, rather than the other way around.
Geology http://doi.org/bmt3 (2016)
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Analysing ancient air in salt crystals. Nature 535, 469 (2016). https://doi.org/10.1038/535469a