An ancient salt rock has revealed that the rise of oxygen in the Earth’s atmosphere 2 billion years ago was “substantial”.

The Earth faced its “most dramatic event ever” 2.3 billion years ago when the atmosphere became oxygenated for the first time.

The Great Oxidation Event happened very rapidly and, until now, scientists did not know just how high the oxygen concentration was after the event.

Research groups, led by the Universities of St Andrews and Princeton, discovered that the rise in oxygen was “much more substantial” than was previously thought.

The University of St Andrews. Image: Claire Hutchison

Dr Clara Blättler, a postdoctoral research fellow in the Department of Geosciences at Princeton, said: “We now have the most quantitative picture yet of Earth two billion years ago.

“It impacts our understanding of the evolution of life on Earth and of the feedbacks between cycles and climate.”

The findings were published in Science on March 22 and found that, after a sharp rise in oxygen, the concentration was similar to that of today.

The oxygen levels were discovered by analysing the chemistry of a 2-billion-year-old cyrstalised salt rock from Russia.

The rocks were found in a 1.2-mile-deep hole in the Karelia region, in the Northwest.

Dr Mark Claire, an atmospheric chemistry lecturer at University of St Andrews, said: “These are the oldest evaporates found by well over a billion years in the entirety of geologic history.

“They are salts; they are very easy to dissolve.

“So the fact that they have been preserved for 2 billion years is really cool.”

Scientists agree that there is still more to be learned about this time period.

Despite the sharp rise in oxygen, animal life did not form for another 2 billion years.

Claire said: “2 billion years is a long time.

“If there was enough oxygen in the atmospheres and oceans, what took it so long for complex life to emerge?”