Oxygen overshot on Earth 2.3bn years ago, and that should have killed some. They are still here

Earth witnessed the Great Oxygenation Event around 2.3 billion years ago, boosting oxygen levels that allowed new life forms to take root. Before this, oxygen levels on our planet were on a much lower scale. This shift meant that the organisms that had already evolved to create energy now needed to adapt to an entirely different atmosphere. To understand how they managed to do so, a group of scientists went on an expedition in Japan. They gathered data on five iron-rich hot springs that they say are potentially "windows into ancient microbial ecology." These springs were chosen as they mimicked ancient oceanic environments during the Great Oxygenation Event. They could also provide insights into ancient microorganisms and how life could form on other planets. “These iron-rich hot springs provide a unique natural laboratory to study microbial metabolism under early Earth-like conditions during the late Archean to early Proterozoic transition, marked by the Great Oxidation Event,” Shawn McGlynn, a study author, said in a statement.

The researchers from the Earth-Life Science Institute and the Institute of Science, Tokyo, found an element in these springs which is rare on Earth today. This element is what helped them survive the Great Oxygenation Event, scientists believe. They are naturally rich in ferrous iron and also have low levels of oxygen and a near-neutral pH. This is exactly what the environment would have been like on Earth during the mega shift. The study authors note that these iron-rich ecosystems proved to be the main reason that helped the microorganisms make it to the other side despite a major change. Also Read: Yellowstone supervolcano mapping reveals scale of future eruptions: 'Things can change within...'

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Hot springs in Japan carry clues of ancient ecosystems

Iron-oxidising bacteria were found to be the dominant microbes in four of the five hot springs. Ferrous iron was the main energy source for the organisms, while cyanobacteria, which produce oxygen, were only sparingly found. "Our results show that in the presence of ferrous iron and limited oxygen, communities of microaerophilic iron oxidisers, oxygenic phototrophs, and anaerobes consistently coexist and sustain remarkably similar and complete biogeochemical cycles," Fatima Li-Hau, study co-author, said in a statement. However, the fifth hot spring threw up completely opposite results.

At the fifth site, non-iron-based metabolisms were found to be dominant. Despite this one anomaly, the scientists believe that not only do their findings offer a window into the early ecosystems, but also show that microbes may have harnessed energy from iron oxidation and oxygen produced by early phototrophs.