The question goes beyond science, it is of a philosophical, metaphysical nature. Man has always asked himself: How did life appear on our planet? What are the ingredients and the recipe that made it possible for something that will become a living being to gush out of the great cauldron?
Researchers at the University of Nice-Sophia Antipolis have succeeded in recreating an "artificial comet" from ice, one of the essential building blocks of life, in the laboratory. It has long been suspected, but this is the first time that it has been possible to show that ribose, a complex sugar that forms the basis of the genetic material of living organisms, has been able to form in cometary ice.
Po achieve this result, scientists from the Nice Institute of Chemistry (CNRS/University Nice Sophia Antipolis) have very precisely analyzed an artificial comet created by their colleagues at the Institute of Space Astrophysics (CNRS/University Paris-Sud). In collaboration with other teams, including one from the SOLEIL synchrotron at Gif-sur-Yvette, they are presenting the first realistic scenario for the formation of this essential compound, which has never before been detected in meteorites or cometary ice. An important step in understanding the emergence of life on Earth.
The scientists presented their recipe in the journal Science on Friday, April 8, 2016. Take grains of sand similar to those found on comets. They should be very small (one tenth of a micrometre). You surround your grains of sand with water ice, a little methanol and ammonia and then you light them with ultraviolet light at very low temperatures. This is done to reconstruct the conditions of the stellar nebulae, where these grains form. Keep an eye on your thermometer, it should be at -195° C. Once this step has been completed, you warm it up slightly in order to volatilize the products obtained and to get closer to the conditions of a comet that warms up as it approaches the sun. And now, observe what you get in your broth.
Surprise of the researchers who expected to find only what is already known, and in particular amino acids: but they discover sugars! That is to say, assemblies of several atoms of carbon and oxygen. How did they discover these molecules that had gone unnoticed by all scientists? To analyse the composition of the result of their recipe, they went to Grasse. It's not far from Nice and it's the home of perfumers. And yet, they use the technique of multidimensional gas chromatography coupled with time-of-flight mass spectrometry almost daily. The barbaric name of a tool used by perfumers to study the composition of essential oils.
By having the idea of using this technology, the scientists from Nice have managed to identify more than 4000 compounds, whereas before, they had laboriously observed only 300. This is why the sugars had remained invisible for so long in all the experiments carried out until then.
In the sugars found at the bottom of the pot, the researchers discovered (presumably shouting for joy and jumping up and down in a frantic jig...) ribose. This is the essential link in the RNA chain, where R means ribonucleic.
All living organisms on Earth, as well as viruses, have a genetic heritage made up of nucleic acids - DNA or RNA. RNA, considered more primitive, is believed to be one of the first characteristic molecules of life to appear on Earth. Scientists have long wondered about the origin of these biological molecules. According to some, the Earth was "seeded" by comets or asteroids containing the building blocks needed to construct them. And indeed, several amino acids (a constituent of proteins) and nitrogenous bases (one of the constituents of nucleic acids) have already been found in meteorites, as well as in artificial comets, reproduced in the laboratory.
But ribose, the other key component of RNA, had never before been detected in extraterrestrial material or produced in the laboratory under "astrophysical" conditions. By simulating the evolution of the interstellar ice that makes up comets, and by succeeding in forming ribose, the French research teams have taken an important step towards understanding the origin of RNA and thus the origins of life.
While the existence of ribose in real comets has yet to be confirmed, this discovery completes the list of "molecular building blocks" of life that can be formed in interstellar ice. It adds another argument to the theory of comets as a source of organic molecules that made life possible on Earth... and perhaps elsewhere in the Universe.
Questioned by The WorldAndré Brack, Honorary Research Director of the CNRS, a specialist in the chemical origin of life on Earth, welcomes this discovery but tempers our fantasies. We should not imagine that life appeared all roasted on Earth, after being put into the first ice ages of the Solar System. The most likely scenario is that a meteor shower arrived on Earth, bringing an avalanche of very ancient organic matter. According to him, this would have formed a layer nearly 30 metres thick. We had to wait for the right conditions (water, solar radiation, heat...) for this inert matter to come to life and become capable of reproducing. But this is still a mystery.