Now scientists are almost sure that life originated on Earth. This was preceded by the spontaneous appearance of biological molecules, which required a lot of energy. Ancient lightning probably served as its source – but a new study has shown that at first there may not have been so many of them.
In 1952, young graduate student Stanley Miller and his venerable, already Nobel Prize-winning supervisor, Harold Urey, conducted a landmark experiment. In a pair of connected glass flasks, they recreated the conditions that supposedly existed on Earth 3.8 billion years ago: the chemical composition of gases, heat and electrical discharges. Scientists believed that this was enough for the spontaneous appearance of the first biological molecules on the then lifeless Earth.
The Harold-Urey experiment was a resounding success: their apparatus immediately produced several amino acids, the building blocks for proteins. As a result, an unknown graduate student, Miller, immediately became the sole author of an article in the leading scientific journal Science (an unprecedented achievement for a young scientist) and hit the front pages of the world media.
However, over time, scientists doubted that the experiment was carried out correctly. Miller and Urey used methane and ammonia as the gas mixture, but later researchers came to the conclusion that the first atmosphere of the Earth, in fact, consisted mainly of carbon dioxide and nitrogen.
Now, the famous experience, which at one time made the front page of The New York Times, has received another serious blow: from the new publication it follows that the initial atmosphere was not very conducive to the occurrence of lightning. Therefore, the appearance of the first biological molecules took longer than previously thought. This also means certain difficulties for the origin of life.
Electrons, participants in all chemical processes without exception, behave differently in different environments. Therefore, in a mixture of methane with ammonia or carbon dioxide with nitrogen, chemical transformations occur in different ways. The question remained open of how different the behavior of electric discharges is in such mixtures. Obviously, the differences could affect the course of abiogenesis – the emergence of the first life from inanimate matter.
To deal with this, Christoph Köhn and his colleagues at the Technical University of Denmark created a model that describes the probability of a streamer, the initial stage of lightning formation. It turns out that in an atmosphere of carbon dioxide, this process occurs more slowly.
“Basically, in an atmosphere with a high content of nitrogen and carbon compounds, a large potential difference would be required for an electrical discharge to occur,” said Kyon.
The fact is that under such conditions, electrons collide less often: this leads to a slower accumulation of electric charges sufficient to form discharges. Transferring this result to the ancient atmosphere, scientists conclude that there could have been noticeably less lightning on the young Earth. This also means a lower probability of abiogenesis.
“If electrical discharges were indeed involved in the appearance of the first prebiotic molecules, we need to properly understand what was happening at that time,” continues Kyon. “And the big question still remains: how did all those prebiotic compounds come about?”
The new work of Danish researchers is just the beginning. It is devoted to only one of the initial stages of the occurrence of lightning, the team plans to study the remaining stages of this complex process, as well as modeling its connection with chemical transformations.
