Geologists studying rocks in Scotland have claimed that the atmosphere of the earth contained enough oxygen for the development of complex life nearly 1.2 billion years ago- 400 million years earlier than previously believed.

Rocks studied by geologists retained signs of bacterial activity which occur only when there is abundant atmospheric oxygen.

The researchers told the journal Nature that the microbes' behaviour was seen 400 million years further back in time than previously thought.

Adrian Boyce from the Scottish Universities Environmental Research Centre said that the research would help them understand the evolution of Earth's atmosphere and the life it sustained.

Speaking on the findings, Boyce said, "Our findings., will give impetus to further investigations into the timescale of the development of complex life."

The findings, published in the November 11th Nature, could lead researchers to review the requisites for life on Earth and other planets.