RNA can form spontaneously when component molecules are filtered into basaltic glass, and that could explain the origin of life on Earth - and point us to where to look for it on other planets, according to new research.
The researchers admit that the discovery does not give all the answers, but argue that it provides a simple and clear answer to one of the biggest questions in science.
Evolutionary theory and genetics combine to explain how the simplest forms of life could have evolved to form the world we know today. However, they have not answered how these first forms of life appeared, something that is difficult to understand.
The nucleotides that form the basis of DNA and RNA have already been found in meteorites, but explaining how they formed is a far more difficult task. A paper in the journal Astrobiology claims to fill in the missing gaps by demonstrating that basaltic glass causes nucleoside triphosphates to join together to form RNA chains.
Earth had a significant amount of basaltic glass when life arose. "For several hundred million years after the moon's formation, frequent impacts coupled with abundant volcanism on the young planet formed molten basaltic lava, the source of basaltic glass," coauthor Stephen Mojzsis, a professor at the University of Colorado, said in a statement. "The impacts would also havemade water evaporate and gave rise to dry land, providing aquifers where RNA could have formed."
The authors demonstrated an impressive synthesis rate for RNA molecules of 90-150 nucleotides in length at 25° C (77° F) and a pH of 7.5, with some lengths reaching 300 nucleotides.
With sufficient feedstock, "a small impact region on the Hadean surface containing just a few metric tons of fractured glass and water permeate could have the capacity to produce about one gram of RNA per day," the authors write.
Meanwhile, evidence for the presence of nucleotide bases in certain meteorites continues to mount, suggesting that they may have arrived on Earth from space. These bases transform into nucleosides in reduced atmospheres, such as those that existed on Earth after asteroid impact.
Team members had previously shown that nickel, abundant in some meteorites, catalyzes nucleosides and phosphate to form triphosphates.
RNA and the origin of life
However, this still leaves open the question of whether these RNA molecules were enough to give rise to life. Biologists have long postulated the idea of an "RNA World", where RNA would have preceded DNA and the proteins it forms.
It remains to be seen how much RNA needs before it can sustain Darwinian evolution, with estimates ranging from 50 to 5,000 nucleotides. Even if the minimum were greater than the chains demonstrated here, it is easy to imagine slightly different circumstances that could give rise to longer chains.
If the article is correct, we owe thanks to basalt for our existence. Other materials present on the early Earth, such as quartz, do not make nucleotides bond in the same way.
Mars was equally rich in basaltic glass at the equivalent period in the history of the two planets. And unlike Earth, much of it remains near the surface, available for assessment on future missions.