RNA can spontaneously form when component molecules filter through basaltic glass, and this could explain the origins of life on Earth – and tell us where to seek it on other worlds, according to new research. The researchers admit the discovery leaves some questions unanswered, but argue it provides a clear and surprisingly simple answer to one of the biggest questions in science.
Evolutionary theory and genetics combine to beautifully explain how the most simple life forms could evolve into the world we see today. However, they have left unresolved how those first life-forms could appear, a point endlessly repeated by creationists mocking the idea of “something coming from nothing”. Even non-creationists see a problem, with RNA's structure described as; “A prebiotic chemist's nightmare”
The nucleotides that form the basis of DNA and RNA have been found in meteorites, but explaining how they come together has proven much harder. A paper in the journal Astrobiology claims to fill that most vital of gaps, showing basaltic glass causes nucleoside triphosphates to come together into chains of RNA.
One thing the Earth did not lack around the time life appeared was basaltic glass. “For several hundred million years after the Moon formed, frequent impacts coupled with abundant volcanism on the young planet formed molten basaltic lava, the source of the basalt glass,” said co-author Professor Stephen Mojzsis of the University of Colorado, Boulder, in a statement. “Impacts also evaporated water to give dry land, providing aquifers where RNA could have formed."
No extreme conditions are required – the authors demonstrated an impressive synthesis rate for RNA molecules 90-150 nucleotides long at 25º C (77º F) and a pH of 7.5, with a few reaching lengths of 300 nucleotides.
Given sufficient raw materials; “A small impact region on the Hadean surface containing just a few metric tons of fractured and water-permeated glass could have had the ability to produce close to a gram of RNA per day,” the authors write. Consequently, they conclude; “Polyribonucleotides were available to Hadean environments if triphosphates were.”
Meanwhile, evidence for the presence of nucleotide bases in certain meteorites continues to grow, suggesting these could have been delivered to the early Earth from space. These bases turn into nucleosides in reduced atmospheres, such as existed on the early Earth after asteroid impacts. Members of the team previously demonstrated that nickel, abundant in some meteorites, catalyzes nucleosides and phosphate to form triphosphates.
This leaves the question of whether these RNA molecules were sufficient to spark life. Biologists have long postulated an “RNA World” where RNA preceded DNA and the proteins it forms. There remains debate as to how long RNA needs to be before it can support Darwinian evolution, with estimates ranging from 50 to 5,000 nucleotides. Even if the minimum is longer than the chains demonstrated here, it's easy to imagine slightly different circumstances could give rise to longer chains.
"The beauty of this model is its simplicity. It can be tested by highschoolers in chemistry class," said Firebird Biomolecular Science's Dr Jan Špaček who was not involved in this study directly.
If the paper is right, we really do have basalt to thank for our existence. Other materials present on the early Earth, such as quartz, did not cause nucleotides to bond together in the same way.
Mars was equally rich in basaltic glass at the equivalent point in the two planets' history. Unlike on Earth, much of this remains close to the surface, available for checking by future missions.