🌍 The origin of life on Earth could be much simpler than thought

The origin of the first living molecules on our planet has long been debated. However, recent experiments are revealing new information about the plausible conditions on the early Earth.

This research provides details on one of the major hypotheses concerning the emergence of life: the RNA world. It suggests that the necessary ingredients, combined with very common minerals and simple hydrological cycles, could have led to the assembly of ribonucleic acid.

An experiment rooted in early geology

Researchers reproduced a plausible environment of the Earth more than four billion years ago in the laboratory. To do this, they mixed the chemical precursors of RNA (namely ribose, a 5-carbon sugar, phosphate, and the four fundamental nucleobases: adenine, guanine, cytosine, and uracil) with specific compounds: borates, present in ancient oceans, and basalt, an ubiquitous volcanic rock.

This mixture was then subjected to repeated wet and dry cycles. These cycles were intended to replicate the transitions our planet experienced in the past near geothermal aquifers and subsurface areas. The team observed that this process allowed for the formation of RNA chains with no other human intervention than placing the ingredients in a test tube.

The work, published in Proceedings of the National Academy of Sciences, reveals that contrary to previous belief, borates did not block the synthesis. On the contrary, they played a stabilizing role for ribose, a naturally fragile sugar that degrades easily. This stabilization allowed ribose to remain available to form the backbone of the RNA molecule, an essential preliminary step.

Basalt, for its part, served as a surface on which the reactions could occur with greater efficiency. This synergy between simple chemical ingredients and a common geological substrate demonstrates that the prebiotic synthesis of RNA did not require an exceptional set of circumstances but could emerge from a common planetary environment.

Cosmic implications for the emergence of life

Scientists maintain the idea that a collision of Earth with a protoplanet rich in organic materials could have simultaneously provided the necessary precursors and the energy required to initiate the chemical reactions needed to create life.

From this perspective, the scope of these discoveries goes beyond Earth. Indeed, space missions that have enabled sample return, such as OSIRIS-REx, have confirmed the presence of ribose and other RNA building blocks in asteroidal material. These complex organic molecules therefore exist in space, reinforcing the idea that they could have been delivered in the same way to other rocky planets by impacts similar to those our planet experienced.

Furthermore, Mars shared with the early Earth a similar context of intense bombardment. The detection of borates on its surface by rovers, coupled with the ancient presence of liquid water, indicates that the ingredients and conditions necessary for this prebiotic chemistry were also present there. The formation of RNA, or analogous molecules, could therefore have been a possibility on our planetary neighbor.

To go further: What is the "RNA World" hypothesis?

This hypothesis suggests a key step in the long journey toward life. It imagines a period where RNA molecules, capable of both carrying information and catalyzing simple chemical reactions, existed and evolved, before the appearance of the first cells.

It is important to understand that the spontaneous formation of RNA molecules, as promising as it may be, does not in itself constitute the creation of life. It rather represents the assembly of a sophisticated molecular tool. Life, as we define it, requires a delimited system, capable of metabolism, self-maintenance, and reproduction with variation.

The "RNA World" hypothesis proposes that this tool could have been the starting point. RNA molecules capable of copying themselves, even imperfectly, could have initiated a process of molecular natural selection. The most stable sequences or those replicating most efficiently would then have taken over.

This hypothetical step is therefore considered a possible bridge between ordinary chemistry and evolutionary biology. It does not solve the riddle of the origin of life by itself, but it identifies a plausible candidate for the first actor in a much longer and more complex story.