How could the first organic molecules that became the basis of terrestrial biology have arisen? A study now sheds light on the possible role of asteroid dust that once rained on our planet. The model simulations indicate that this “rich” material could have accumulated heavily in ice melt holes in the early Earth. There, the special substance cocktail may have triggered the prebiotic chemistry that was at the beginning of the development of life, say the researchers.
Life always produces new life – but how did the first step come about? How inanimate matter once formed complex compounds that enabled self-replication and metabolism is still a mystery. In principle, it seems clear that the complex organic molecules initially formed through chemical processes: it is assumed that in the first 500 million years of Earth’s history, prebiotic chemistry produced RNA, DNA, fatty acids and proteins. These building blocks may then have functionally combined, creating the first biological units. However, the previous formation of the basic building blocks does not appear to be inevitable. In order for these complex organic molecules to be created through chemical reactions, relatively high concentrations of the elements nitrogen, sulfur, carbon and phosphorus are necessary. But corresponding cocktails can hardly be formed from earthly material because it does not contain high levels of these substances.
Life elements from space
However, there has long been speculation that asteroids could have provided the relevant quantities, because they are demonstrably rich in the elements necessary for life. But this explanation is controversial. Because as chunks, meteorites only deliver the substances in a limited environment. The research team led by Craig Walton from the Swiss Federal Institute of Technology in Zurich has therefore looked at another possibility: dust from broken asteroids could have become “fertilizer” for prebiotic processes on Earth. So far, however, there has been the objection that the material was scattered too widely to provide relevant quantities of the substances. “But if you take into account processes that could have led to a concentration, things look different,” says Walton.
To shed light on the extent to which cosmic dust could have supplied prebiotic chemistry, Walton and his colleagues have now developed model simulations. This included assumptions about the extent of the former dust rain. Even today, around 30,000 tons of cosmic dust particles fall to Earth from space every year. But according to the researchers, it can be assumed that in the early history of our planet’s development, millions of tons fell from the then frequent collisions of asteroids. The models also incorporated assumptions about the conditions on the young Earth as well as data on possible accumulation processes of cosmic dust. “Recent research has provided evidence that the Earth’s surface cooled and solidified very quickly and large ice sheets formed,” says Walton.
Dust primordial soup in ice melting holes
As the team reports, the simulations made it clear that areas with significant dust concentrations could have formed, which were also continuously supplied with supplies. The once ice-covered areas of the earth emerged as the best places for the accumulations. In particular, an effect could have come into play that is still known today in glaciers and ice sheets: the ice surfaces often appear dirty and, especially in the holes where meltwater collects, sediments that were previously blown onto the ice accumulate heavily. The simulations show that cosmic dust could once have been highly concentrated in such so-called cryoconite holes.
As the researchers explain, the relevant elements could have been released from the dust particles in these cryoconite holes. As soon as their concentration in the water reached a critical threshold, chemical reactions could have started on their own, leading to the formation of the organic molecules at the origin of life, the scientists say. The low temperatures would not have been unfavorable either: “Cold does not harm organic chemistry, on the contrary. Reactions are more selective and specific at low temperatures than at high ones,” explains Walton. For example, it has already been shown that complex organic molecules can actually form at certain substance concentrations and temperatures around freezing point.
Walton and his colleagues hope that their thesis will once again stimulate the discussion about the origins of terrestrial biology: “Our study will probably cause controversy. But it may also lead to new ideas about the origin of life,” says Walton. He and his colleagues plan to support their theoretical results with experimental data. Specifically, they want to recreate the conditions that might have existed in the prehistoric melting holes in laboratory vessels and then examine whether biologically relevant molecules are formed.
Source: Swiss Federal Institute of Technology Zurich, specialist article: Nature Astronomy doi: 10.1038/s41550-024-02212-z