How life on earth began

The story of us begins with a whimper. So insignificant, in fact, scientists think we started out completely by chance.

In a laboratory at Wits University scientists believe they have replicated how life began before a time when there were tissues, cells or even DNA.

And it was no earth-moving big bang, just a couple of molecules hooking up.

PhD student Nisha Dhar and Pierre Durand from the Evolution of Complexity Laboratory in the Evolutionary Studies Institute at Wits University studied how small strands of molecules linked up to form larger molecules that had the ability to replicate themselves.

"These complex molecules by a chance event would have been able to reproduce themselves," said Durand, adding that this would be the point at which life is seen to begin to evolve.

Their research appeared on Wednesday in the journal Royal Society OS.

In the past five years Dhar and Durand have been working to find out just how these molecules linked up.

It is all part of theory of the evolution of life known as the RNA World Hypothesis. This puts forward the theory that RNA molecules were the start of the evolution of DNA and proteins. RNA is made from nucleic acids.

"This is a well-known model system [RNA world hypothesis] for studying the origin of life. There is a lot known about it, but also a lot is missing," said Durand. "Nisha picked one aspect of this hypothesis of how larger molecules evolved from smaller molecules."

They found RNA molecules had enzymes, allowing what is called ligation, which enabled them to join with other molecules.

Molecules of RNA had to be replicated billions of times in the laboratory so they would be observed.

"The small molecules are very promiscuous and can join other pieces to themselves. What was interesting was that these smaller molecules were smaller than we had originally thought," said Durand.

This event is believed to have taken place possibly 4billion years ago, at a time when a young earth was a hostile place with a volcanic activity and an atmosphere that had yet to contain oxygen. RNA, said Durand, was hardy and would have survived these kinds of conditions.

"This probably would have happened along the shoreline, in pools of water, although some people believe it might have even happened on clay," Durand said.

Francis Thackeray, of the Institute for Human Evolution at Wits, said that surprisingly what Durand and Dhar had discovered was suggested by Charles Darwin 146 years ago. This is a journey that continues.

"We need to understand what led to the very origins of life," said Thackeray.