Scottish rocks record ancient oxygen clues

Oxygen levels on Earth reached a critical threshold to enable the evolution of complex life much earlier than thought, say scientists.

The evidence is found in 1.2-billion-year-old rocks from Scotland.

These rocks retain signatures of bacterial activity known to occur when there is copious atmospheric oxygen.

The microbes' behaviour is seen 400 million years further back in time than any previous discovery, the researchers tell the journal Nature.

The team is not saying complex life existed 1.2 billion years ago, merely that the conditions would have been right for it to start to take hold. ...

via BBC News - Scottish rocks record ancient oxygen clues.