Anyone who’s ever noticed a water puddle drying in the sun has seen an environment that may have driven the type of chemical reactions that scientists believe were critical to the formation of life on the early Earth.
The important molecules of contemporary life, known as polypeptides, can be formed simply by mixing amino and hydroxy acids – which are believed to have existed together on the early Earth – then subjecting them to cycles of wet and dry conditions.
This simple process, which could have taken place in a puddle drying out in the sun and then reforming with the next rain, works because chemical bonds formed by one compound make bonds easier to form with the other.
The research supports the theory that life could have begun on dry land, perhaps even in the desert, where cycles of nighttime cooling and dew formation are followed by daytime heating and evaporation.
Just 20 of these day-night, wet-dry cycles were needed to form a complex mixture of polypeptides in the lab. The process also allowed the breakdown and reassembly of the organic materials to form random sequences that could have led to the formation of the polypeptide chains that were needed for life.
“The simplicity of using hydration-dehydration cycles to drive the kind of chemistry you need for life is really appealing,” said Nicholas Hud, a professor in the School of Chemistry and Biochemistry at the Georgia Institute of Technology. “It looks like dry land would have provided a very favorable environment for getting the chemistry necessary for life started.”
Origin-of-life scientists had previously made polypeptides from amino acids by heating them well past the boiling point of water, or by driving polymerization with activating chemicals.
But the high temperatures are beyond the point at which most life could survive, and the robust availability of activating chemicals on the early Earth is questionable. The simplicity of the wet-dry cycle therefore makes it attractive to explain how peptides could have formed, Hud added.