How life begins remains unresolved issue. One of the key components may be RNA, a molecular relative of DNA found in all forms of life on Earth, and now scientists say they have shown how it may have formed on our planet centuries ago. But not everyone is convinced, and RNA may be just one of many molecules that could give rise to life on different worlds.
In the newspaper published today at Proceedings of the US National Academy of Sciences.Astrobiologist Yuta Hirakawa and colleagues describe how conditions on Earth about 4.3 billion years ago may have been ideal for the emergence of life. In their experiment, they showed that as a result of a strong impact on the Earth, RNA could be formed, and then life.
The steps outlined by the team suggest that “RNA is an integral product of planets everywhere,” says Stephen Benner of the Foundation for Applied Molecular Evolution (FfAME) in Florida, a co-author of the paper. And this, in turn, “will mean that life is everywhere.” Unlike proteins, which carry out most of the chemical processes in modern cells, and DNA, which stores genetic information, RNA can do both—one reason it was long considered promising candidate for the first molecule of life.
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Hirakawa's research team prepared test tubes containing an aqueous mixture of materials similar to those thought to be common on the early Earth, then heated them and allowed them to dry. The mixtures included a chemical soup of ribose sugar, nucleic acid bases, a reactive source of phosphorus, and a mineral compound called borate.
The process of heating and drying was “ubiquitous on the early Earth,” Hirakawa says. “So this reaction had to happen.” The result of the experiment was the formation of RNA-like molecules, which, with minimal further chemical reactions, could become RNA itself. The team says it shows RNA can form naturally, not far from the dawn of our planet.
Lee Cronin, an expert in prebiotic chemistry at the University of Glasgow who was not involved in the work, said he was unsure of the results because human input was required to source and mix the various components. “The fact that they reverse engineered RNA synthesis under the right conditions doesn't say anything,” he says. “The plausibility rationale is false.”
One of the key findings in the paper is that the borate compound does not inhibit the formation of life-precursor materials, as previously thought, but actually promotes the production of RNA. “Borate is very important for stabilizing sugars, which are unstable molecules,” says Hirakawa, also noting that reactions with borates can produce ribose phosphate and dehydrated phosphate, two key molecules for subsequent RNA synthesis. “The most important finding of my research is that borate facilitates these reactions.”
Researchers also discovered borate on Marswhich raises the possibility that life could have arisen independently on the Red Planet, Benner says. “Earth's early atmosphere was not very different from what we have now on Mars,” he says.
However, the research team's hypothesis still requires strong external influence. Namely, a large object falling to Earth would be the most obvious way to deliver RNA precursors. They calculated that something the size of the asteroid Vesta, located in the asteroid belt, should have been enough. This impactor would have been separated from and much smaller than the Mars-sized object that is believed to have caused the impact. formation of the Moon as a result of a collision with the Earth. The known physics of planet formation strongly suggests that medium-sized impacts like the one proposed in the new study were relatively common during Earth's early eras.
This means, Benner says, that it is likely that other rocky planets also experienced impact events that could lead to similar conditions. “The argument is that the impact story is universal,” he says. “As the planet increases a small portion of its orbit around the star, it clears its territory,” acquires RNA precursors and appears to prepare RNA. And if this scenario is true, he says, it “means there is life everywhere, including in billions of other stars like the Sun. [in the Milky Way that] There are almost certainly rocky planets.”
According to the team, the most notable result of the proposed large impact would be the molecules needed to convert ribose, a sugar, into ribose phosphate.
Recent analysis of samples of the asteroid Bennu collected by NASA's OSIRIS-REx spacecraft in 2020 and returned to Earth in 2023 also found revealed the presence of ribose on this asteroid. The discovery also suggests that ribose was present on the early Earth, says Yoshihiro Furukawa of Tohoku University, who led the discovery of ribose and was also a co-author of the new paper, because Bennu points to the same type of primordial material that originally formed our planet. “Meteorites like Bennu would therefore have been the building blocks of life on prebiotic Earth,” he says.
Cronin, however, says Benner and the new study still rely on human input for RNA production, even if it appears to be the result of a natural process. And even with all the right ingredients, he says, the chances of producing RNA are actually extremely low without human intervention, akin to getting a royal flush in a game of poker. “The mathematical probability of finding RNA anywhere else in the universe is virtually zero,” Cronin concludes.
Instead, he says, many other molecules besides RNA may be ingredients for life on other worlds. “RNA is a very boring molecule,” he says. “There's nothing special about it, and there are plenty of alternatives that could do the job.”
However, the role of borate in this process is “very interesting,” Cronin adds. “The work of borate researchers is enormous,” he says. “It shows how strange things can create molecules that we didn't even know existed.”
