By analyzing a suite of forgotten samples, university and NASA scientists found a new answer to a longstanding question in prebiotic chemistry. The samples were from reactions performed in 1958 by Dr. Stanley Miller; these reactions were variations on his well-known spark discharge experiments, which demonstrated that amino acids and other important prebiotic molecules could be formed by adding electrical energy to a variety of atmospheric conditions that could have existed on the prebiotic Earth. A challenging question for prebiotic chemists to answer is how amino acids (or other monomers such as DNA or RNA nucleotides) can be combined into polymers called peptides. The condensation of amino acids into peptides produces water and water is the solvent for these reactions, and, in fact, all life as we know it. This poses a challenge, because net reaction rates slow down when there is a high abundance of product molecules in the system (Le Chatelier’s principle). Thus, the condensation of amino acids in water proceeds only very slowly.
Cyanamide is a condensing agent, a molecule that accelerates the rate of condensation reactions even in water. In the samples analyzed in the current study, Miller added additional cyanamide to his normal mix of gases for a round of spark discharge experiments, but the samples were not analyzed at the time. They surfaced some 50 years later and were now available for study. Eric Parker and co-workers (including myself) analyzed the archived samples and discovered that, in addition to the amino acids commonly produced by the spark discharge experiments, a number of small peptides were also produced. Importantly, cyanamide is also product of the spark discharge reactions, meaning that it is produced concurrently with the amino acids in the spark discharge experiments. Therefore, the spark discharge experiments simulate a plausible way to make peptides from simple gases such as nitrogen, hydrogen and methane, improving our understanding of how molecules important for the origins of life could be generated on a variety of terrestrial bodies in our universe.