Buried inside ancient grains of rock salt, a team of geologists has discovered traces of a breathable, animal-friendly atmosphere. If confirmed, the finding will push back the rise of oxygen on Earth hundreds of millions of years, raising new questions about the evolution of complex life both here and beyond our solar system.
Earth may be our cosy blue marble today, but hop in a time machine and travel back two billion years, and you’d soon asphyxiate from a lack of oxygen. While scientists have found traces of oxygen on Earth dating back more than three billion years, it took eons of microbial activity before the air became anything close to what we’d consider breathable.
According to models and indirect geochemical evidence, atmospheric oxygen levels rose sharply toward the end of the Neoproterozoic era some 600 million years ago, closely coinciding with the appearance of marine animals in the fossil record. But a new study published in the journal Geology calls that date—and its tight link to the emergence of multicellular life—into question.
By analysing air bubbles trapped inside 815-million-year-old grains of halite, or rock salt, geologists at the University of Aberdeen and elsewhere have now produced the oldest direct measurements of an oxygen-rich atmosphere. The ancient air samples have oxygen contents ranging from 10.3 to 13.1 per cent, more than five times higher than what scientists had previously estimated for the mid Neoproterozoic. (Our modern atmosphere is approximately 21 per cent oxygen.)
“I think our results will take people by surprise,” study co-author Nigel Blamey, told Science News. “We came out of left field, and I think some people are going to embrace it, and other people are going to be very sceptical. But the data is what the data is.”
If the finding can be supported by additional samples in other locales, it’d imply a substantial gap between rise of oxygen and the rise of animals during the Cambrian explosion, suggesting that some other preconditions needed to be met before complex life could take over.
And that would have profound implications for the discovery of complex life beyond our solar system. With Earth as our only example to go on, one might assume that complex life always follows an oxygen-rich atmosphere. If it turns out that’s not the case, then biospheres like our own and beings like ourselves may be less cosmically common than we hope. [University of Aberdeen News via Science News]