It might be that what set prebiotic chemistry in motion and kept it going in the early days of the Earth was dust from outer space accumulating in holes melted into ice sheets. NOMIS Fellow Craig Walton and researchers at ETH Zurich and the University of Cambridge have used a computer model to test this scenario. Their findings were published in Nature Astronomy.
by Peter Rüegg
Before life existed on Earth, there had to be chemistry to form organic molecules from the chemical elements nitrogen, sulphur, carbon and phosphorus. For the corresponding chemical reactions to start and be maintained, these elements had to be present in abundance – and constantly replenished. On the Earth itself, however, these elements were and still are in short supply.
In fact, the elementary building blocks of life were so rare that chemical reactions would have quickly become exhausted, if they indeed ever managed to get going at all. Geological processes such as erosion and weathering of the Earth’s constituent rocks were also unable to ensure a sufficient supply, as the Earth’s crust simply contained too few of these elements. Nevertheless, in the first 500 million years of Earth’s history, a prebiotic chemistry developed that produced organic molecules such as RNA, DNA, fatty acids and proteins, on which all life is based.
Ingredients from outer space?
Where did the required quantities of sulphur, phosphorus, nitrogen and carbon come from? Geologist and Nomis Fellow Craig Walton is convinced that these elements came to Earth primarily as cosmic dust.
This dust is created in space, for example when asteroids collide with each other. Even today, around 30,000 tonnes of dust still fall to Earth from space each year. In the early days of the Earth, however, the dust rained down in much greater volumes, amounting to millions of tonnes per year. Above all, however, the dust particles contain a lot of nitrogen, carbon, sulphur and phosphorus. They would therefore have the potential to set a chemical cascade in motion.
However, the fact that the dust disperses widely and can be found only in very small quantities in any one place speaks against this. “But if you include transport processes, things look different,” Walton says. Wind, rain or rivers collect cosmic dust over a large area and deposit it in concentrated form at certain locations.
Continue reading this ETH Zurich story: Do we have cosmic dust to thank for life on Earth?
Read the Nature Astronomy publication: Cosmic dust fertilization of glacial prebiotic chemistry on early Earth
Feature image: An asteroid is breaking up, producing a lot of dust, which reaches the Earth eventually. (Image: NASA / JPL-Caltech)
