Research that has recreated in the laboratory the conditions that prevail in cosmic molecular clouds has proven that the basic mechanisms of life can develop in the extreme conditions of space and that life is not a condition unique to planets like Earth.
New research has shown that amino acids can form peptides, the building blocks of life, in space, suggesting that life as we know it may have originally formed in space, and not just on our planet.
Current theories about the origins of life state that amino acids were transported by comets and meteorites that seeded the Earth in the first moments of its formation, and that these acids were then converted into peptides due to the favorable conditions that existed then. on our planet.
The new research challenges this assumption, as it has been able to determine that the conversion of amino acids into peptides can occur in space. It is not necessary for a planet like Earth to exist for life to germinate in another part of the universe, concludes this research.
The origin of life remains one of the great mysteries of science, more than 4,000 years after it began to form on our planet.
According to current theories, early in the formation of our planet there was a ‘primordial soup’ with simple chemicals that would produce amino acids. These became the proteins needed to create the cells that, in turn, gave rise to plants and animals.
What has never been determined is how the amino acid ‘building blocks’ were assembled into the proteins that formed the cellular machinery and early life forms.
What the new research, carried out by scientists at the Friedrich Schiller University of Jena and the Max Planck Institute for Astronomy, both in Germany, says is that amino acids can be converted into more complex peptides, a key component of life, in the harsh space conditions. The results have been published in Nature Communications.
As explained by the authors of this research, the amino acids, nucleobases and various sugars found in meteoroids, for example, show that their origin could be extraterrestrial in nature.
However, they add, for a peptide to form from single amino acid molecules, very special conditions are required that were thought to be more likely to exist only on Earth.
Until now, those conditions included the presence of water, mainly because every time one amino acid base combines with another to form a peptide chain, a molecule of water must be removed.
“Water plays an important role in the conventional way peptides are created,” explains Serge Krasnokutski, one of the researchers, in a statement.
“Our quantum-chemical calculations have shown that the amino acid glycine can be formed through a chemical precursor, called amino ketene, which combines with a water molecule. Bottom line: In this case, water must be added for the first reaction step and water must be removed for the second.”
… and without water
This set of contradictory circumstances forced the researchers to look at the origin of the peptides in a completely different and direct way, eliminating one of the two steps and the process water altogether.
“Instead of taking the chemical turn where amino acids are formed, we wanted to find out if aminoketene molecules could be formed and combined directly to form peptides,” Krasnokutski says.
“And we did it under the conditions that prevail in cosmic molecular clouds, that is, in dust particles in a vacuum, where the corresponding chemicals are present in abundance: carbon, ammonia and carbon monoxide.”
To test this hypothesis, the team used an ultra-high vacuum chamber, which would allow them to simulate the environment of space by lowering it to about one trillionth of normal air pressure and minus 263 degrees Celsius.
Inside the chamber, they placed artificial substrates that served as models of dust particles like those found in interstellar space.
When the researchers introduced carbon, ammonia and carbon monoxide molecules to the surfaces of simulated dust particles, they witnessed the one-step conversion of individual glycine amino acids to the polyglycine peptide chain. And all without the introduction of water.
“Investigations showed that under these conditions, the polyglycine peptide was formed from simple chemicals,” says Krasnokutski. “These are therefore chains of the very simple amino acid glycine.”
“And we looked at different lengths,” adds Krasnokutski regarding the complexity of the peptides seen in his experiments. “The longest specimens consisted of eleven units of the amino acid.”
According to the research team, the success of this one-step, waterless conversion relies primarily on an “extremely reactive” amino acid: amino ketene.
“The fact that the reaction can take place at such low temperatures is because aminoketene molecules are extremely reactive,” Krasnokutski said. “They combine with each other in an efficient polymerization. The product of this is polyglycine.”
The researchers say they found it surprising that this aminoketene polymerization could occur under such extreme, space-like conditions, primarily because of the energy barrier this conversion has to overcome.
However, they suspect that something may be happening on a very small scale, a phenomenon known as quantum tunneling, that is helping the amino acid get around that energy barrier and form actual peptide chains.
“It may be that a special effect of quantum mechanics helps us in this”, explains Krasnokutski referring to the so-called tunnel effectwhereby an elementary particle can de facto pass through a wall.
“In this special reaction step, a hydrogen atom changes places. However, it is so small that, as a quantum particle, it could not overcome the barrier, but could simply tunnel through it, so to speak.”
If the results of this study were confirmed beyond the laboratory, it would mean that amino acids probably do not need the conditions that existed on early Earth to combine into complex molecules.
Instead, it’s possible that those conditions already exist within interstellar space, and that early Earth simply needed to cool down enough for those building blocks of life to take hold.
If this assumption is true, it would mean that the “origin of life” not only remains an unanswered question, but that the answer is no longer to be found solely on our planet.
Now that it’s clear that not only amino acids but also peptide chains can be created under cosmic conditions, we may have to look not just to Earth to get to the bottom of the origin of life, the researchers conclude.
A pathway to peptides in space through the condensation of atomic carbon. SA Krasnokutsk et al. Nature Astronomy (2022). DOI:https://doi.org/10.1038/s41550-021-01577-9