NMMU scientist disproves ‘hot earth’ theory

FOR the past three decades, scientists have maintained that the sea was hot when life first began on Earth some 3.5 billion years ago – somewhere between a scorching 30°C and 80°C.

But at the same time, research has shown that the sun was much less intense, generating about 25% less heat than it does today.

For the Nelson Mandela Metropolitan University’s (NMMU) Professor Maarten de Wit, the two theories just did not add up.

“The planet should have been frozen unless the atmosphere was dense with greenhouse gases.”

So, with co-researcher Harald Furnes from the University of Bergen in Norway, he sought proof in the rocks of the Barberton greenstone belt, exposed in the Makhonjwa Mountains in Mpumalanga, which are among the oldest on earth, and arguably contain the earliest fossils.

The two have just published a paper in the journal Science Advances which disproves the earlier “hot earth” theories.

Working on the Barberton rock records, which would once have lain at the bottom of a deep ocean, over the past six years, they found two particular pieces of evidence against the hot-ocean theory.

The first was the discovery of hydrothermal pipes that formed in a deep ocean environment – which suggest the hot water in question did not come from the ocean, but rather from hydrothermal vents that sprang from the earth’s volcanic crust 2km to 4km below the ocean surface, and were active at about 200°C, “just as we find in modern oceans”, De Wit said.

They also found hydrothermal fields of slightly younger age, which would have operated as hot springs near and above sea level, between about 30°C and 270°C .

Quite separately, they also discovered evidence of glacial deposits, at and above sea level, and sulfate minerals like gypsum in the ocean sediments deposited 2km to 4km below sea level, which today only grow in deep-sea environments where there is cold water.

These key findings disprove the earlier theory and present a new one: that the sea was cold – and that life was already thriving and may even have originated in this cold sea.

“What is unique in our findings is that there is evidence from both deep oceans and shallow oceans that ocean water was cold,” De Wit said. Using paleomagnetic signatures in the ancient rocks, the scientists were able to determine that they would have formed somewhere near the equator.

“We don’t have glaciers at surface level at the equator,” he said.

“This shows there was a very special cold period in the planet as a whole – the whole world was cold.”