Tag : Fluctuating

Washington: A new research has shed light on one of the reasons why animal evolution accelerated millions of years ago and according to scientists it is the wild fluctuations in the oxygen levels a billion years ago that could be held responsible. Scientists believe atmospheric oxygen developed in three stages, starting with what is known as the Great Oxidation Event around two billion years ago, when oxygen first appeared in the atmosphere. The third stage, around 400 million years ago, saw atmospheric oxygen rise to current levels. What is uncertain is what happened during the second stage, in a time known as the Neoproterozoic Era, which started about one billion years ago and lasted for around 500 million years. During this time, early forms of animal life emerged. 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? Fossilised traces of early animals - known as Ediacaran biota, multi-celled organisms that required oxygen - have been found in sedimentary rocks that are 541 to 635 million years old. To try to answer the question, a research team at the University of Leeds supported by the Universities of Lyon, Exeter and UCL, 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 produ ...