Basic building blocks had to exist for the formation of the first living beings on our planet - but how could they have arisen? An experimental study now shows that precursors of biological molecules could have formed under the influence of iron particles from meteorites and volcanic ash. Under the possible atmospheric conditions of the young earth, the metal therefore acted as a catalyst for the conversion of carbon dioxide into biologically relevant substances. The process could have contributed significantly to the potential for the emergence of the first organisms, the researchers say.
It is one of the most fundamental questions in science: How did the first cell-like structures on earth form, which eventually replicated themselves and then took on increasingly complex forms? According to the current state of knowledge, the development of life probably began surprisingly early on the still young planet. The basis was formed by organic molecules that could serve as building blocks for the first organisms. Previous research suggests that the precursors to these substances may have been supplied by asteroids or formed by certain reactions on early Earth. But there are still many unanswered questions about the possible mechanisms.
Information from the chemical industry
The inspiration for the current study on this topic came from industrial chemistry, reports senior author Oliver Trapp from the Ludwig Maximilian University of Munich (LMU). Specifically, he wondered whether the so-called Fischer-Tropsch process could have had a counterpart in the carbon dioxide-rich earth's atmosphere around 4.4 billion years ago. In this process, hydrocarbons are produced from carbon monoxide and hydrogen with the help of metallic catalysts. The inquiring gaze was directed to iron particles from meteorites or volcanic ash, which could have acted as catalysts. These are substances that accelerate certain chemical reactions, but are not consumed in the processes.
"When I looked at the chemical composition of the Campo del Cielo iron meteorite, it was clear to me that it could represent a perfect Fischer-Tropsch catalyst," says Trapp. Another possible carrier substance for the catalytically active metal was volcanic ash. "There should have been plenty of fine ash particles in the atmosphere and on the first land masses of the earth," says co-author Dmitry Semenov from the Max Planck Institute for Astronomy in Heidelberg. The first author of the study, Sophia Peters from the LMU, then dealt with the experimental investigation of the possible processes. She used meteorite samples and iron-rich volcanic ash from Mount Etna as test materials. The test substances were ground to relevant sizes and mixed with various minerals as a carrier substance. Each substrate was then placed in a pressure chamber filled mostly with carbon dioxide but also with some hydrogen to simulate early Earth's atmosphere. The mixing ratio as well as the pressure and temperature were varied from experiment to experiment.
Catalyzed formation of organic molecules
As the team reports, the analytical studies of the reaction products revealed: Thanks to the iron catalyst from the meteorite and the ash material, organic compounds were produced in considerable quantities: methanol, ethanol, acetaldehyde and formaldehyde. The two latter substances in particular are known to be important building blocks for fatty acids, nucleobases (genetics), sugar substances and amino acids, the scientists emphasize.
It was also shown that these reactions proceeded successfully over a wide range of pressure and temperature conditions. "Since there are many different possibilities for the properties of early Earth, I tried to experimentally test every possible scenario," says Perters. The fact that the organic molecules formed under such different conditions is strong evidence that such reactions may have occurred on early Earth, the scientists say.
The team concludes that another mechanism is now emerging that, along with others, could once have contributed to the basic material potential for the formation of organisms. The sources of the molecular building blocks that have been possible so far include hydrothermal vents on the sea floor, electrical discharges in the atmosphere and the transport of organic compounds by celestial bodies from space. The researchers say that future investigations could now look more closely at the question of which of the various mechanisms could have provided the highest yield of building blocks under realistic conditions.
Source: Max Planck Institute for Astronomy, specialist article: Scientific Reports, doi: 10.1038/s41598-023-33741-8