Wet-dry cycles could have allowed for synthesis of building blocks for RNA on early Earth

A team of researchers with members from institutions in Germany, the U.K. and Japan has developed a new theory to explain how RNA could have originated on early Earth. In their paper published in the journal Science, the group outlines what they describe as a plausible sequence of events that could have led to the natural synthesis of the building blocks of RNA. Nicholas Hud and David Fialho with the Georgia Institute of Technology have published a Perspective piece on the work done by the team in the same journal issue.

Most scientists who have studied the origins of life agree that the emergence of RNA was most likely the beginning of all life on Earth. But how RNA came to exist is still under debate. Most theories start by noting that RNA is made from purine and pyrimidine nucleosides—both are needed for information transfer during replication. Thus, for RNA to have developed, both materials would have to exist simultaneously and mix in the right way in order for RNA to form correctly. Unfortunately, most theories that describe how such materials could have originated are unable to explain how they could have coexisted in just the right way. In this new effort, the researchers suggest they have found the answer—wet/dry cycles.

The researchers propose that on prebiotic Earth, there were nucleoside precursors for both purine and pyrimidine—and both were mixed with ribose and exposed to wet/dry cycles in which humidity levels rose and fell. Such exposure would have led to evaporation of a liquid solution of reactants during higher temperatures, forcing them to coalesce into highly concentrated material, almost suitable for working together to create RNA. They suggest the addition of reagents such as iron and hydrogen sulfide could have provided the means (inducing a rearrangement of the materials to allow for a cytosine nucleoside) for allowing the precursors to become nucleoside precursors—and from there, to become purine and pyrimidine in a form that could not just exist together, but work together to build RNA.

The researchers note that unlike theories involving meteorite impacts or volcanic explosions, wet/dry cycles would occurred on a regular basis on all exposed lands, making the proposed process more plausible.