When life emerged, it did so quickly. Fossils suggest microbes were present 3.7 billion years ago, just a few hundred million years after the 4.5 billion-year-old planet cooled enough to support biochemistry, and many researchers think the hereditary material of these early organisms was RNA. While not as complex as DNA, RNA would still be difficult to forge into the long strands needed to transmit genetic information, raising the question of how it might have formed spontaneously.
Now, researchers may have an answer. In laboratory experiments, they show how rocks called basaltic glasses help individual letters of RNA, known as triphosphate nucleosides, to bind into strands up to 200 letters long. Spectacles would have been abundant in the fire and sulfur of the early Earth; they are created when the lava is blown out in the air or water or when the molten rock created in the asteroids hits it cools rapidly.
The result divided the best researchers on the origin of life. “This seems to be a wonderful story that finally explains how triphosphate nucleosides react with each other to give RNA strands,” says Thomas Carell, a chemist at the Ludwig Maximilian University of Munich. But Jack Szostak, an RNA expert at Harvard University, says he won’t believe the result until the research team better characterizes the RNA strands.
Origin-of-life researchers love a primordial “RNA world” because the molecule can carry out two distinct life-giving processes. Like DNA, it is made up of four chemical letters that can carry genetic information. And like proteins, RNA can also catalyze the chemical reactions necessary for life.
But RNA also brings headaches. No one has found a set of plausible prebiotic conditions that would cause hundreds of RNA letters, each of them complex molecules, to bind into strands long enough to support the complex chemistry needed to trigger evolution.
Stephen Mojzsis, geologist at the Research Center for Astronomy and Earth Sciences of the Hungarian Academy of Sciences, he wondered if basaltic glass played a role. They are rich in metals such as magnesium and iron which promote many chemical reactions. And, he says, “Basaltic glass was everywhere on Earth at that time.”
He sent samples of five different basalt glasses to the Foundation for Applied Molecular Evolution. There, Elisa Biondi, a molecular biologist, and her colleagues ground each sample into a fine powder, sterilized it and mixed it with a triphosphate nucleoside solution. Without a glass powder present, the letters RNA failed to connect. But when mixed with the glass powders, the molecules join into long strands, several hundred letters long, the researchers report this week in Astrobiology. There was no need for heat or light. “All we had to do was wait,” Biondi says. Small strands of RNA formed after just one day, but the strands continued to grow for months. “The beauty of this model is its simplicity,” says Jan Špaček, a molecular biologist at Firebird Biomolecular Sciences. “Mix the ingredients, wait a few days and detect the RNA”.
However, the findings raise many questions. One is how triphosphate nucleosides might have arisen in the first place. Biondi’s colleague Steven Benner says recent research shows how the basaltic glasses themselves may have promoted the formation and stabilization of individual RNA letters.
A bigger problem, Szostak says, is the shape of the long RNA strands. In modern cells, enzymes ensure that most RNAs grow in long linear chains. But RNA letters can also bind in complex branching patterns. Szostak wants the researchers to report the type of RNA created by the basaltic glasses. “I find it very frustrating that the authors made an interesting initial discovery, but then decided to follow the hype rather than the science,” says Szostak.
Biondi admits that his team’s experiment almost certainly produces a small amount of RNA branching. However, he notes that some branched RNAs exist in organisms today and related structures may have been present at the dawn of life. He also says that other tests performed by the group confirm the presence of long wires with connections which most likely mean they are linear. “It’s a healthy debate,” says Dieter Braun, an origin-of-life chemist at Ludwig Maximilian. “It will trigger the next round of experiments.”
Correction, June 6, 4pm: An earlier version of this story misrepresented Stephen Mojzsis’ affiliation.