New experimental evidence is strengthening the RNA world hypothesis, a long-standing idea that places RNA at the center of how life first emerged on Earth. The findings suggest that RNA, one of life’s most essential molecules, may have formed naturally on our planet around 4.3 billion years ago and could be widespread throughout the universe.
RNA, or ribonucleic acid, plays a crucial role in modern biology, particularly in protein synthesis. Compared to DNA, RNA is structurally simpler. It appears in three primary forms: messenger RNA, which carries genetic instructions from DNA; ribosomal RNA, which forms the core of ribosomes; and transfer RNA, which assembles proteins based on those instructions.
Because of its relative simplicity and functional versatility, RNA is widely believed to have preceded DNA. Its ability to store genetic information and catalyze chemical reactions has positioned it as a central element in theories about the origin of life. This idea is commonly referred to as the RNA world hypothesis, which proposes that early life relied on RNA for replication and genetic storage before DNA-based systems evolved.
Despite its appeal, explaining the formation of RNA under early Earth conditions has proven difficult. The spontaneous assembly of RNA requires a precise sequence of chemical reactions, making its natural emergence seem highly improbable. To address this challenge, chemists have searched for reaction pathways that could reliably produce RNA without biological assistance.
One proposed route is the six-step Discontinuous Synthesis Model. However, this pathway faced a major obstacle in the form of borates, common compounds found in seawater. Borates are negatively charged oxyanions containing boron and oxygen, and they were previously thought to interfere with key chemical reactions needed to form RNA.
A research team led by Yuta Hirakawa from Tohoku University and the Foundation for Applied Molecular Evolution has now challenged that assumption. Their experiments indicate that borates may actually support RNA formation rather than prevent it.
The team combined RNA’s basic components, including ribose sugar, phosphates, and the four RNA nucleobases, with borates and basalt. The mixture was then heated and dried, replicating conditions believed to have existed near underground aquifers on the early Earth. Under these conditions, RNA molecules successfully formed.
The results showed that borates helped stabilize ribose, which is typically prone to degradation, and aided phosphate production. These effects supported key stages of the Discontinuous Synthesis Model, directly contradicting earlier assumptions about borates being harmful to RNA formation.
The findings align with recent discoveries from NASA’s OSIRIS-REx mission, which returned samples from the asteroid Bennu. Scientists recently confirmed the presence of ribose in the Bennu material, meaning all known components of RNA have now been identified in extraterrestrial samples.
Hirakawa’s team proposes that a massive protoplanet impact, involving an object roughly 500 kilometers wide and rich in RNA ingredients, could have delivered these building blocks to Earth in large quantities. They estimate this event occurred about 4.3 billion years ago, shortly after Earth formed and well before the oldest known evidence of life preserved in ancient zircon minerals.
Previously, RNA synthesis in laboratories required deliberate human intervention to initiate chemical reactions. The researchers argue that this study marks the first instance of RNA forming under laboratory conditions without direct human manipulation, although some critics maintain that assembling the ingredients still constitutes intervention.
Large asteroid impacts were also common on early Mars, and borates have been detected there as well. This raises the possibility that the chemical conditions necessary for RNA formation once existed on the Red Planet.
While RNA itself is not considered life, it is fundamental to nearly all known living systems. If RNA emerged rapidly on the early Earth, it may have accelerated the appearance of the planet’s first simple organisms, offering a crucial stepping stone in the origin of life on Earth.
