Researchers have long debated how the molecular components needed for life came to exist in the bleak environment of the early Earth about 4 billion years ago. Researchers now present experimental evidence for a new possibility—that metals from iron-rich meteorites pelting the planet from above, as well as from volcanic particles spewing from within, catalyzed the fixation of carbon dioxide, the dominant gas in the atmosphere at the time. This helped build basic carbon-containing molecules such as hydrocarbons, aldehydes, and alcohols, which could then perform the reactions that generated more complex biotic molecules.
“We have closed a gap in the story of initiating life,” says Oliver Trapp, a chemist at Ludwig Maximilian University of Munich, who led the work (Sci. Rep. 2023, DOI: 10.1038/s41598-023-33741-8).
The idea hit Trapp like a meteorite—literally. One day about 6 years ago, he was examining a meteorite he had purchased that was part of the Campo del Cielo, a cluster of meteorites thought to have fallen to Earth more than 4,000 years ago in Argentina. Reading the certificate listing the rock’s components–92% iron, 7% nickel, 0,5% cobalt, and a sprinkle of iridium—he imagined a meteorite hurtling through the atmosphere. It would slow down and heat up, causing the outside of the rocks to form nanoparticles. “Of course, these nanoparticles are highly reactive,” Trapp says. “I immediately realized this was the perfect Fischer-Tropsch catalyst.”
To test their idea experimentally, he and his colleagues made nanoparticles from meteorites and from volcanic ash and minerals. They put these materials into chambers that simulated a variety of atmospheric and climate conditions of that time—specifically, different atmospheric pressures and temperatures, different ratios of CO2 and hydrogen, and wet versus dry climate conditions. Across climate scenarios, the iron and other metals in the meteorite and ash particles catalyzed the synthesis of prebiotic molecules.
“Under [all] these conditions you are getting really, really similar compositions of these oxygenated compounds, which are really nice building blocks that can continue to generate chemistry,” Trapp says. Based on the rate of reactions observed, as well as estimates from other studies of ancient meteorite activity, the researchers calculated that this mechanism could have churned out 600,000 metric tons of these molecules per year, for tens to hundreds of millions of years. The team is now conducting large-scale simulation models and experiments to explore what kinds of reactions this initial prebiotic mixture molecules might have undergone and what larger compounds it might have produced.
“It’s surprising that chemists haven’t until recently systematically looked at how inorganic volcanic and meteoritic particles react with CO2,”, says Joseph Moran, a chemist at the University of Strasbourg. “The early Earth was producing hydrogen and hydrogenation catalysts were literally raining down from the sky,” Moran says. “Perhaps it is no coincidence that very ancient organisms were running their metabolisms on hydrogenation.”