New Pathway to Hydrogen Cyanide on Early Earth Unveiled

To explore this question, a research team led by Professor Ryuhei Nakamura of Institute of Science Tokyo (Science Tokyo) focused on amino acids, which are thought to have been abundant on early Earth. The team examined 38 different minerals, including minerals found in deep-sea hydrothermal vent deposits ("chimneys") and minerals originating from meteorites.

The researchers discovered that manganese dioxide (MnO₂), a common mineral, helps oxidize amino acids, producing HCN as a reaction product. Remarkably, the reaction proceeded in mild aqueous environments without oxygen gas-conditions similar to those on Earth before life emerged.

The study also showed that not only glycine, the simplest amino acid, but also various other amino acids and short peptides could react with MnO₂ to produce HCN. In other words, amino acids themselves-already considered important ingredients for life-may also have helped generate another key ingredient for life.

This study suggests that even if methane levels were low on early Earth, chemical reactions needed to produce the building blocks of life could still have taken place. Previous studies showed that amino acids could break down into substances such as ammonia (NH₃) and carbon dioxide (CO₂), but they rarely produced HCN. In other experiments using electricity, scientists detected cyanide groups (-CN) attached to the surfaces of gold or platinum electrodes. However, these surface-bound molecules were not the "free" HCN needed to react with other molecules and help build the chemistry of life.

In the new study, MnO₂ played a special role. The research team carefully investigated whether the detected HCN truly came from amino acids and which part of the amino acid molecule was transformed into HCN. The team focused on glycine (NH₂CH₂COOH), the simplest amino acid, which contains two carbon atoms. By labeling each carbon atom and tracking the reaction, the researchers found that the carbon in the CH₂ group was converted into HCN. This result revealed a previously unknown reaction pathway in which MnO₂ specifically interacts with the CH₂ part of amino acids.

This research addresses one of science's biggest questions: how did life begin? The discovery of an HCN formation pathway that does not depend on methane could provide new clues not only about early Earth, but also about the possibility of life-forming chemistry on other planets such as Mars.

The findings may also have practical applications. HCN is an important industrial chemical used in metal extraction and chemical synthesis. In the future, this reaction could contribute to technologies that convert plant-derived amino acids into useful chemicals, as well as more sustainable methods for resource mining.

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