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Billion-year-old air has five times more oxygen than expected

Scientists have, for the first time, been able to directly analyze the atmosphere of Earth from nearly a billion years ago. No, you did not miss the invention of time travel. A team of Canadian researchers developed a technique to recover microscopic pockets of air from ancient salt crystals, and they reveal Earth had a lot more oxygen than we thought in those days.

The atmosphere right now is about 20% oxygen. It’s been higher at various points over the eons, but a billion years ago it was thought to be just a fraction of that. The recovered samples, however, showed 10.9% oxygen. That’s about five times higher than expected.

The samples were recovered from drill cores collected in Australia and dated to around 815 million years. The gas in these cores was trapped during a geological era known as the Neoproterozoic. Just like today, when salt water evaporated, it formed salt crystals known as halites. These crystals are very stable and can trap tiny bubbles of liquid and air. Ice can also trap air pockets, but the problem with ice is that it melts. These salt crystals were buried by sediment and waited nearly a billion years to be unearthed by scientists.

These crystals were taken to Brock University where Nigel Blamey has built a one-of-a-kind machine that can crush tiny samples of rock — as little as a tenth of a gram — and analyze the gas released from them. He took multiple samples from the Australian halite and measured the gases inside. To validate the experiment, he also tested modern halite samples, which have known gas compositions.

The higher level of oxygen in the ancient samples could have major implications for the history of life on Earth. 815 million years ago, there were no complex multicellular life forms — at least none that we know of. With more oxygen, it would be possible for such creatures to survive. It’s plausible that if we look hard enough, we could find complex fossils that are much older than the ones we’ve found so far.

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