Artist's impression of the early Earth conditions that the Miller-Urey experiment tried to recreate. Credit: CSIC.
Some of the basic ingredients for life are well known: a dash of water, methane, ammonia, hydrogen and a spark. But a pinch of minerals is also needed, according to a new study1 by Italian and Spanish researchers that recreated an experiment from 1952, paying attention to a detail that had been overlooked for all these years: the glass pot in which it was performed.
“In science you should take nothing for granted,” says Raffaele Saladino, a professor at Tuscia University and president of the Italian Society of Astrobiology. “Nobody would have guessed that a setting tested hundreds of times could tell us anything more.” In 1952 at the University of Chicago, Stanley Miller and Harold Urey simulated the Earth’s environment 4.6 billion years ago to study abiogenesis, the natural synthesis of organic molecules such as amino acids and nucleobases (the building blocks of proteins and DNA/RNA respectively). In a sealed flask, they recreated the primordial atmosphere along with water, while a spark simulated lightning. Later, they found several amino acids, demonstrating how the precursors of life could emerge in a prebiotic soup. “In some experiments Miller also noted the presence of silica [the main component of glass and some rocks],” says Saladino, “but he didn’t pay much attention to it.” And nobody else investigated its role until now.
In previous studies, the team found that silica and its minerals in a solution similar to Miller’s could facilitate the process. So they decided to test the idea that, in the original experiment, they had been diluted from the flask because of the causticity of the mixture. They repeated the experiment using three containers made of materials with different pHs: borosilicate glass or Pyrex (the same material used by Miller), Teflon, which is an inert material, and Teflon with some borosilicate bits in the solution. The results confirmed that organic matter emerged in every flask independently of the pH, but the Teflon container had the fewest products, followed by the one with glass pieces. The abundance of organic molecules in the Pyrex container – 56 different kinds, amino acids and nucleobases included – was staggering, with some molecules appearing only in the borosilicate glass, revealing the importance of minerals as hidden ingredients for the precursors of life. “It makes sense, if we want to simulate a realistic scenario,” explains Saladino, “because we would have the atmosphere, water, lightning, but what we missed was the rock containing the water.”
A renewed interest in abiogenesis could help the search for life on other planets. “The complexity of a molecule doesn’t guarantee that it was produced by biological processes,” notes Saladino. “If we were able to create such molecular richness with a single experiment, then finding molecules like glycine or phosphine on other planets wouldn’t necessarily imply that they were synthesized by a living organism.” Future studies will test which molecules can emerge in a Miller-Urey setting using different minerals and alien atmospheres. Then, when looking for life on different planets we will better know what molecules to expect and, more importantly, those that are truly unexpected.
