London: Scientists have found that oxygen had reached a level where it could have supported life much earlier than thought – 400 million years further back in time.
The evidence is found in 1.2-billion-year-old rocks from Scotland, which show signatures of bacterial activity known to occur when there is copious atmospheric oxygen.
This is not to say that complex life existed 1.2 billion years ago, merely that the conditions would have been right for it to start to take hold.
"We`re recording a key stage in the evolution of life on Earth. The evidence relates to a particular group of microbes that have been very successful through Earth`s history and are now found everywhere from glaciers to the deep ocean floor,” the BBC quoted Professor John Parnell from the University of Aberdeen as saying.
"These microbes made an important advance by becoming more efficient, which they did through using oxygen in their environment. So the occurrence of these microbes is a marker for increasing oxygen in the atmosphere," he added.
The researchers do not see the fossil evidence of the microbes themselves - only the chemical traces that they were present and using sulphur in the lake floor as a form of energy.
"There`s a certain stage which is achieved by bacteria when they start to work in a more complex way, and they do this by forming a community where some bacteria are turning sulphate into sulphide and there`s another lot of bacteria turning the sulphide back to sulphate," explained Parnell.
"What we are now showing is that the conditions in the atmosphere were in place [1.2 billion years ago], so it probably needed some other factor to trigger the early evolution of complex life and the fact that the Ediacaran fauna occur after the ``snowball Earth`` episode suggests those two are linked somehow," he said.