Charles Darwin thought it started in a warm pond. Others point to comets that ploughed into Earth. And some suspect a bolt from the blue, a lightning strike into the ocean.
How life started on Earth may forever be a mystery, but new research proposes a radical idea: that crashing waves and waterfalls may have kicked off the process by throwing up mists of water.
In experiments at Stanford University, chemists discovered that microdroplets in fine sprays of water generate streaks of “microlightning”. When surrounded by the right mix of gases, these sparks power chemical reactions that synthesise many molecules for life.
Prof Richard Zare, a chemist who led the team, said: “This is a real contribution to understanding how you can go from non-life to life. You have water sprays all over the place, particularly around rocks, and there are crevices in rocks where these chemicals can accumulate.”
There is no consensus about the origins of life, and no shortage of hypotheses. When Darwin published On the Origin of Species in 1859 he described how evolution generated the diversity of life, but not how it started. He speculated, however, that chemicals could have interacted in “a warm little pond” from which living cells eventually emerged.
Hot undersea vents that spew mineral-rich fluids are now considered to be leading contenders for fostering life. Impacting comets may have helped, too, by creating shock waves that converted simple organics into amino acids, the constituents of proteins.
Lightning strikes might also have lent a hand. The idea that lightning created the ingredients for life gained traction in 1953 when Stanley Miller and Harold Urey at the University of Chicago reported that electrical discharges in a simulated early Earth atmosphere produced amino acids. But the hypothesis has its critics: lightning is too infrequent, they say, and the chemicals produced simply drift away.
Zare’s team took to a dark room to investigate the electrical properties of water sprays. They found that droplets carry opposing charges and when they come together, tiny sparks leap between them. Unlike lightning bolts that cover miles, microlightning travels a few billionths of a metre.
While the effect is faint, it carries enough energy to drive chemical reactions. Writing in Science Advances, the researchers describe how they sprayed water into a mixture of nitrogen, methane, carbon dioxide and ammonia. This led to the rapid formation of key molecules including hydrogen cyanide; glycine, an amino acid involved in protein production; and uracil, a building block of RNA found in all living cells. “We propose that this is a new mechanism for the prebiotic synthesis of molecules that constitute the building blocks of life,” Zare said.
Dr Eva Stueeken, who studies the origins of life at the University of St Andrews, said the work was fascinating. “It opens up an array of possibilities that we need to explore further, using different gas and fluid compositions,” she said. “It will also be important to quantify how significant this mechanism would have been on a global scale for the generation of prebiotic molecules.”
Prof David Deamer at the University of California, Santa Cruz, who has worked with Zare but not on the latest study, said microlightning “can now be added to the list of possible energy sources available to drive organic synthesis before life began”.