Four billion years ago, Earth was a chaotic, lifeless world — a fiery hell with spewing volcanoes and meteorite impacts dominating the landscape. The atmosphere was filled with noxious fumes from these volcanoes, including hydrogen sulfide, methane, and ten to 200 times as much carbon dioxide as today’s atmosphere.

It’s hard to imagine how life appeared in this hellscape, but somehow it found a way. How? A new hypothesis suggests that tiny sparks of electricity, leaping between water droplets, could have jump-started the chemical reactions that gave rise to the basic building blocks of life.

A New Twist on an Old Idea for the Origin of Life

The new research from Stanford University builds on the famous Miller-Urey experiment of 1952, which showed that lightning-like electrical sparks could transform simple gases into amino acids, the building blocks of proteins. Lightning striking in Earth’s early oceans might have seeded these chemicals that eventually became RNA and the first life forms. But critics have long argued that lightning strikes were too rare and the oceans too vast for this to be a plausible explanation.

Richard Zare, a chemist at Stanford, and his team offer a compelling alternative.  They discovered that when water is sprayed into the air — as might happen with crashing waves or waterfalls on early Earth — the droplets develop opposing electrical charges. Larger droplets tend to carry positive charges, while smaller ones become negatively charged. When these droplets come close together, electrons leap between them, creating tiny flashes of electricity. They have called these sparks “microlightning.”

“We usually think of water as so benign, but when it’s divided in the form of little droplets, water is highly reactive,” Zare said.

Lightning in a droplet

Using high-speed cameras, the researchers captured these fleeting sparks, which are invisible to the naked eye. They then sprayed water into a chamber filled with gases thought to mimic Earth’s early atmosphere — nitrogen, methane, carbon dioxide, and ammonia. The microlightning triggered chemical reactions that produced hydrogen cyanide, the amino acid glycine, and uracil, a component of RNA. Nothing as intense and dramatic as lightning seems to be required to catalyze these reactions.

“On early Earth, there were water sprays all over the place — into crevices or against rocks, and they can accumulate and create this chemical reaction,” Zare said. “I think this overcomes many of the problems people have with the Miller-Urey hypothesis.”

The new research builds on a long history of science about the strange behavior of water. In 1867, Lord Kelvin observed that water droplets could generate sparks as they fell from a height. More recently, scientists have studied how water droplets can become charged when they interact with air or other surfaces. But until now, no one had fully explored the chemical consequences of these tiny electrical discharges.

The researchers also explored the energy of these microlightning events by testing their ability to ionize various molecules. They found that the sparks could ionize benzene, a molecule with a relatively high ionization energy, as well as other nonpolar molecules like octane and even xenon, a noble gas. The energy is certainly there and enough to do some serious chemistry.

The Spark of Life in a Droplet

This is a completely new way of thinking about how simple molecules could have been transformed into something resembling the complex chemistry of life. Unlike lightning, which is sporadic and localized, water sprays are everywhere. They are in ocean waves, waterfalls, and the mist created by crashing waves. This ubiquity makes microlightning a compelling candidate for driving the chemical reactions that led to the origins of life.

If microlightning can drive chemical reactions on Earth, could it do the same elsewhere? Water is abundant in the solar system, from the icy moons of Jupiter and Saturn to the subsurface oceans of Enceladus and Europa. If these worlds have conditions where water droplets can form and interact with gases, microlightning could be a universal mechanism for prebiotic chemistry.

Next, the researchers plan to continue exploring the potential of microlightning, including its ability to drive other types of chemical reactions. They also hope to study how these processes might have contributed to the emergence of more complex molecules, such as proteins and nucleic acids.

The findings appeared in the journal Science Advances.