2013-12-01 09:45:59
Molecules potentially precursors of amino acids have been detected in comets
How life emerged on planet Earth remains a mystery. Living organisms are very complex systems, made up of molecules that work as a team to survive and reproduce. In this sense, not only the gene molecules, formed by deoxyribonucleic acid, DNA, are replicated in reproduction, proteins and other molecules of life are also replicated. It is the entire living system that reproduces. How the first self-replicating system emerged and what molecules formed it remains unknown, although, from what we know, ribonucleic acid, more popular by its acronym RNA, could have been the nucleus of the first system with the capacity to self-replicate.
However, not only the nature of the first systems capable of replicating is the subject of debate and scientific study. The very origin of life’s simplest molecules remains controversial. In 1953, the famous Miller and Urey experiment, in which these scientists subjected a mixture of gases corresponding to the composition of the primitive Earth’s atmosphere to electrical discharges, demonstrated that it had the necessary components to generate amino acids, the chemical units that form proteins. In experiments carried out between 1959 and 1962, the Spanish scientist Joan Oró also demonstrated that the conditions of the primitive Earth also allowed the generation of the constituent molecules of nucleic acids, DNA and RNA.
However, one thing is that the conditions of the primitive Earth allow the generation of life molecules, and another is that these can be generated in sufficient quantities to give rise to the first living systems. On the other hand, even the origin of terrestrial water, absolutely necessary for life, remains disputed, since it is possible that water was not present at the formation of the planet, 4.5 billion years ago, but rather came from enormous and frequent collisions with icy comets, which occurred about 600 million years later, in a period called the “late heavy bombardment.”
AMINO ACIDS IN COMETS
In fact, precursor molecules of amino acids have been detected in comets, and even NASA’s Stardust space probe was able to collect samples from the surface of comet 81P/Wild-2, in which the presence of glycine, the most important amino acid, was detected. simple, but no less important. What could be the origin of amino acids in comets? Did these amino acids and water contribute to the early Earth, allowing the origin of life?
The synthesis of complex molecules from simpler ones requires energy.
In the cold outer space, far from the Sun, where the comet cloud was located before bombarding the Earth, and where temperatures are very low, the chemical reactions necessary to generate amino acids cannot occur at an appreciable speed. An energy source is necessary that substantially increases the temperature and allows chemical reactions to occur at a higher rate. Where can that energy come from? It is known that if something happened frequently in the early solar system, it was collisions between bodies in orbit around the Sun. The collisions, if they happen at sufficient speed, release a large amount of energy that can partially melt the cometary ice, and perhaps allow the generation of chemical reactions, which could give rise to the detected amino acids.
This hypothesis of chemical synthesis by shock is attractive, but, as with all hypotheses, it cannot be accepted unless we acquire some evidence to support it. This is what a group of researchers from Imperial College London have achieved, who publish their results in the journal Nature Geoscience.
COLLISION GENERATION
The researchers prepared various mixtures of compounds present in comets: water, ammonia, carbon dioxide and methanol, and frozen them at –160ºC, a temperature similar to that which can be found in comets in orbit around the Sun. After being frozen, the Researchers fired, at half a kilo of frozen mixture, a steel projectile at the speed of 7.12 kilometers per second, a speed also on the order of those found in collisions between comets and these with planets. This speed is about ten times greater than that of a bullet fired from a rifle, and is achieved with special gas cannons.
After firing the projectiles at the frozen mixtures, the researchers placed them in an aerated oven at 90ºC to evaporate the water and volatile compounds from the mixtures. If any non-volatile substance had been generated in the collision, it would be deposited in the unevaporated remains. The analysis of these remains revealed, in fact, that the collisions had generated various amino acids in some of the mixtures, although not in all, which indicates that the chemical composition of the comets may be critical for the impact generation of these molecular components. fundamental for life.
Thus, these shocking experiments provide evidence in support of the hypothesis that about 3.9 billion years ago, during the late heavy bombardment, comets not only brought water to the dry Earth, but in their collisions with the planet, they were able to generate also the molecules necessary to form a rich primordial soup from which the first system worthy of being called alive could arise.
NEW WORK BY JORGE LABORDA.
It can be purchased here:
Chained circumstances. Ed. Lulu
Other works by Jorge Laborda
One Moon, one civilization. Why the Moon tells us that we are alone in the Universe
One Moon one civilization why the Moon tells us we are alone in the universe
The intelligence funnel and other essays
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