How Fluctuating Oxygen Levels May Have Accelerated Animal Evolution
Published:31 Oct.2022    Source:University of Leeds
The question scientists have tried to answer is - was there anything extraordinary about the changes to oxygen levels in the Neoproterozoic Era that may have played a pivotal role in the early evolution of animals - did oxygen levels suddenly rise or was there a gradual increase? To try to answer the question, a research team at the University of Leeds used measurements of the different forms of carbon, or carbon isotopes, found in limestone rocks taken from shallow seas. Based on the isotope ratios of the different types of carbon found, the researchers were able to calculate photosynthesis levels that existed millions of years ago and infer atmospheric oxygen levels. 
As a result of the calculations, they have been able to produce a record of oxygen levels in the atmosphere over the last 1.5 billion years, which tells us how much oxygen would have been diffusing into the ocean to support early marine life. Dr Alex Krause, the lead scientist on the project, said the findings give a new perspective on the way oxygen levels were changing on Earth. He added: “our study shows oxygen levels were far more dynamic. There was an oscillation between high and low levels of oxygen for a long time before early forms of animal life emerged. We are seeing periods where the ocean environment, where early animals lived, would have had abundant oxygen -- and then periods where it does not.”