The origins of life on Earth remain one of science's most intriguing mysteries. Recently, new experiments lend support to the 'RNA world' hypothesis, suggesting that RNA—an essential molecule for protein synthesis—could be more prevalent throughout the universe than previously thought. These findings imply that RNA may have formed on our planet around 4.3 billion years ago under conditions that were more favorable than we understood.
RNA, which stands for ribonucleic acid, is a simpler variant of DNA (deoxyribonucleic acid), the molecule responsible for storing genetic information in living organisms. RNA exists in three primary forms: messenger RNA (mRNA), which carries genetic instructions from DNA for protein creation; ribosomal RNA (rRNA), which forms ribosomes necessary for protein synthesis; and transfer RNA (tRNA), which is crucial for assembling proteins based on mRNA instructions.
Despite its significance, understanding how RNA originated has posed various challenges. Researchers have long pondered what might have caused the right ingredients for RNA to combine and undergo the required chemical reactions. At first glance, the likelihood of RNA forming spontaneously seems incredibly low.
To address this puzzle, chemists are investigating possible pathways that could lead to the emergence of RNA-like molecules. One particular pathway, known as the Discontinuous Synthesis Model (DSM), consists of six steps that could potentially result in RNA formation.
A notable hurdle in this pathway has been the role of borates, which are common compounds found in seawater. Borates are classified as oxyanions, meaning they carry a negative electrical charge, and contain both boron and oxygen atoms. For many years, scientists believed that borates inhibited certain reactions needed for RNA formation. However, recent research led by biochemist Yuta Hirakawa from Tohoku University in Japan and the Foundation for Applied Molecular Evolution in Florida challenges this notion, suggesting instead that borates may actually facilitate RNA creation.
In their experiments, Hirakawa's team mixed the fundamental components of RNA—ribose (a five-carbon sugar), phosphates, and four nucleobases (adenine, guanine, cytosine, and uracil)—with borates and basalt, then subjected this mixture to heat and allowed it to dry. This process mimicked what they believe were common environmental conditions near underground aquifers on early Earth.
The results were astonishing: RNA successfully formed within the mixture. Rather than obstructing the necessary reactions, borates appeared to enhance specific steps in the DSM model, such as stabilizing ribose molecules—which can often break down easily—and aiding phosphate production.
These findings gain additional credibility from recent discoveries involving samples collected from the asteroid Bennu by NASA's OSIRIS-REx mission. The identification of ribose in these samples means that all the essential components of RNA have now been found within the 120 grams (about 4.2 ounces) of material that OSIRIS-REx brought back from Bennu.
Hirakawa’s team proposes that the collision of a protoplanet, comparable in size to the asteroid Vesta and rich in RNA-building materials, could have delivered these crucial building blocks to Earth approximately 4.3 billion years ago. This event is believed to have occurred 200 million years after Earth formed and 200 million years before the oldest signs of life, indicated by carbon isotopes found in ancient zircon deposits dated at about 4.1 billion years.
Historically, RNA had only been synthesized in laboratories through human intervention, which intentionally triggered the necessary chemical reactions. Hirakawa’s research claims to represent the first instance of RNA being generated in a lab environment without direct human influence, though critics argue that merely placing RNA's building blocks together in a test tube constitutes human intervention.
It’s worth noting that similar large-scale impacts occurred during the formative years of Mars, suggesting that the building blocks of RNA could also have reached the Red Planet. Interestingly, borates have been discovered on Mars too, which implies that conditions suitable for RNA production may have existed there as well.
While RNA itself is not synonymous with life, it is indispensable for nearly all known life forms. If RNA did indeed arise on Earth in a relatively short geological timeframe, it could have accelerated the emergence of the first simple organisms on our planet.
This groundbreaking research was published on December 15 in the journal Proceedings of the National Academy of Sciences.
Keith Cooper, a freelance science journalist and editor based in the United Kingdom, holds a degree in physics and astrophysics from the University of Manchester. He is also the author of "The Contact Paradox: Challenging Our Assumptions in the Search for Extraterrestrial Intelligence" (Bloomsbury Sigma, 2020) and has contributed articles on astronomy, space, physics, and astrobiology to numerous magazines and websites.
