How life arose from non-living material is one of the most profound mysteries facing science, and now a new study from the University College London (UCL) may have brought us a step closer to understanding it. The team may have solved a long-standing chicken-and-egg riddle related to how different types of peptides and proteins interact to give rise to life.

Evolution can only be traced back so far – at a certain point we have to wonder how life sparked out of lifeless matter. It's generally thought that everything started with a "primordial soup" rich in nutrients, which pooled on the surface or surrounded deep-sea hydrothermal vents. Energy from lightning strikes or volcanic activity can kickstart the process, allowing amino acids to link up, forming peptides that can go on to form proteins and eventually life.

But as the researchers on the new study point out, there's a problem with that story.

"Peptides, which are chains of amino acids, are an absolutely essential element of all life on Earth," says Matthew Powner, lead author of the study. "They form the fabric of proteins, which serve as catalysts for biological processes, but they themselves require enzymes to control their formation from amino acids. So we've had a classic chicken-and-egg problem – how were the first enzymes made?"

To get to the bottom of the conundrum, the researchers ignored amino acids for a moment and focused on their precursors – molecules called aminonitriles. Normally, these molecules begin stacking into amino acids only in either strongly acidic or alkaline environments, and then the amino acids need energy to make peptides.

But the team found that they could skip both of those steps, turning aminonitriles directly into peptides. The process worked in water by combining aminonitriles with hydrogen sulfide and ferricyanide. These two molecules are outgassed by volcanoes, meaning they would likely have been around on early Earth.

"This is the first time that peptides have been convincingly shown to form without using amino acids in water, using relatively gentle conditions likely to be available on the primitive Earth," says Saidul Islam, co-author of the study.

Along with helping us better understand how life arose, the researchers say the technique could be applied to synthetic chemistry, making for more efficient ways to produce materials and pharmaceuticals. The next steps for the team are to investigate other ways to turn aminonitriles into peptides.

The research was published in the journal Nature.