Origins of life traced to a rockpool four billion years ago

One day, about four billion years ago, a miraculous event in the planet’s history occurred.

Somewhere on the earth a string of chemicals folded over, attracted other chemicals into an identical string, and made a copy of itself.

All life on earth derives, it is believed, from that one chemical process.

The question is how did it happen, and where? A team of scientists think they have an answer to the second question, and a clue to the first.

RNA is a chemical present in all our bodies, a little like a simpler version of DNA.

It is crucial for our survival, but scientists believe that it was fundamental to the beginnings of life because despite being easier to make than DNA it also has the potential to replicate itself.

"RNA is always discussed as a potential precursor for life," said Thomas Henning, from the Max Planck Institute for Astronomy in Germany.

"Today’s life is characterised by DNA, but DNA is complex. RNA has the functions needed at the beginning of life."

Once a group of chemicals can copy itself, it opens the possibility of it mutating, improving and becoming complex life.

Some people have suggested that the first RNA may have developed beside undersea hydrothermal vents, but in a paper in the journal Proceedings of the National Academy of Sciences, Professor Henning has shown that there is a better candidate: warm, wet pools.

The early earth was a violent place, with probably billions of times more meteorites hitting it than today. This provided it with the complex molecules necessary to make RNA.

As the chemicals leached out of the meteorites, they needed to form long chains known as polymers.

Professor Henning and his colleagues have modelled the chemistry of "warm wet pools", similar to rockpools, that would be filled up then dried out in cycles, either by rain or tides.

The filling up process would protect them from ultraviolet radiation, while the pools drying out would concentrate the chemicals into a stronger and stronger "soup" - not possible in undersea vents.

Their paper shows, they claim, that this would be enough to make RNA. "As soon as you have warm ponds, in a relatively short period these RNA strands develop," said Professor Henning, who estimated that this "relatively short period" would be 200-300 million years.

If they can show that it is possible for RNA to replicate spontaneously under conditions on earth, then there would be a template for how life could have begun here and on other planets.

"This bombardment we had in the early solar system is similar to other planetary systems. If we can show this is a robust process, where life can form relatively easily under these conditions, the probability of life forming elsewhere is quite high."