A 1.4 billion-year-old sample of oxygen has given scientists fresh evidence of what the Earth's atmosphere and biosphere were like in the lead up to the emergence of animal life.
Teased out of a 1.4 billion-year-old evaporative lake deposit in Ontario, the sample represents the oldest measurement of atmospheric oxygen isotopes by nearly a billion years.
The findings, published in the journal Nature, support previous research suggesting that oxygen levels in the air during this time in Earth's history were a tiny fraction of what they are today due to a much less productive biosphere.
"It has been suggested for many decades now that the composition of the atmosphere has significantly varied through time," explained Peter Crockford, who led the study as a PhD student at McGill University.
"We provide unambiguous evidence that it was indeed much different 1.4 billion years ago."
The findings were uncovered via the scientists collecting pristine samples of ancient salts, known as sulfates, found in a sedimentary rock formation north of Lake Superior.
Crockford shuttled the samples to Louisiana State University, where he worked closely with the research's co-authors Huiming Bao, Justin Hayles, and Yongbo Peng, whose lab is one of a handful in the world using a specialised mass-spectrometry technique capable of probing such materials for rare oxygen isotopes within sulfates.
The results provide the oldest gauge yet of what earth scientists refer to as "primary production," in which micro-organisms at the base of the food chain - algae, cyanobacteria, and the like - produce organic matter from carbon dioxide and pour oxygen into the air.
"This study shows that primary production 1.4 billion years ago was much less than today," added senior co-author Boswell Wing, who helped supervise Crockford's work.
"This means that the size of the global biosphere had to be smaller, and likely just didn't yield enough food - organic carbon - to support a lot of complex macroscopic life."
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