Dr. Robert Riding, research professor in Earth and Planetary Sciences at the University of Tennessee, received a write-up in New Scientist last week for a discovery he and his colleagues made while analyzing rock samples collected from Steep Rock Lake in Ontario, Canada.
Riding’s team found that the limestone from which the samples were taken had not changed in 2.8 billion years. For limestone to form, calcium carbonate must be stripped of all its dissolved iron — a process which can only happen if oxygen is present.
Why is this important? Because oxygen levels didn’t increase on a worldwide scale until 2.4 billion years ago. This is the first evidence of an “oxygen oasis,” which could have helped early life develop a tolerance to the poisonous gas.