Old rocks, new ideas
Once it was thought that Earth's earliest oceans were piping hot but new evidence suggests that they were cold - and this could change our understanding of how life began.
The evidence for these cold seas comes from a study of rocks in the Barberton Greenstone Belt, in Mpumalanga.
Scientists previously thought that 3.5billion years ago the planet's oceans were very hot - at between 30C and 80C - and that it was from them that early life sprang.
But through oxygen-isotope analysis of hundreds of rock samples, some believed to have been formed in glaciers, researchers now believe the opposite is true.
"These Barberton rocks formed near the equator - but there were glaciers. This is not at the poles, so this was a cold earth," said Maarten de Wit, a geologist at Nelson Mandela Metropolitan University, who was a co-author of the paper published in the Journal of Science Advances.
He said the probability of a cold Earth made sense because the sun then radiated less heat than today.
It was in the same rock formations that scientists found the earliest known evidence of life. These were microscopic tubular structures that also date back to 3.5billion years. Scientists suggested then that they evolved next to hot thermal vents.
"My best estimate is that these seas would have been at close to 0C, maybe -1C or -2C," said De Wit.
He said that with life possibly emerging from a very cold environment scientists might have to rethink evolution, and a frigid start to life on Earth bettered the odds that life sprang up elsewhere in the solar system.
"Earth and Mars would have been similar then," De Wit said. "What we have in South Africa is a unique record that the environment for life was already there."