A new study from Stanford University suggests that life may have been started by constant electric shocks generated by "microlightning" between water droplets. The most important missing link in the evolutionary tree is the first: How do living cells arise from nonliving matter? There is a view that the early Earth contained a primordial soup containing the ingredients necessary for life as we know it - all it needed was a specific catalyst to start chemical reactions that turned inorganic compounds into organic matter.
One of the most enduring ideas is that lightning strikes can provide this spark. The groundbreaking Miller-Ulay experiment of 1952 sent an electric shock through a flask containing water and gases (used to represent the early Earth's atmosphere) and found that certain amino acids and other important biomolecules were produced.
But there are some problems with this assumption. If this process occurred in the ocean, the resulting chemicals would be too dilute to initiate life broadly. If it occurs in a shallow pond, the likelihood of a lightning strike in such a small space is slim to none.
In new research, Stanford University scientists propose that the electrical energy may come from a more common and stable source -- something they call microlightning. When water droplets are ejected into the air from things like ocean waves or waterfalls, tiny electrical charges form between them. These tiny electric shocks can trigger complex chemical reactions without the need for any external electricity.
"Microdischarges between microscopically charged water droplets produced all the organic molecules previously observed in the Miller-Ulay experiment, and we believe this is a new mechanism for the prebiotic synthesis of molecules that form the building blocks of life," said Richard Zare, senior author of the study.
To test this idea, the researchers conducted an updated version of the Miller-Ulay experiment. When the experiment began, the tank was filled with gases that simulated the early Earth, including nitrogen, methane, carbon dioxide and ammonia. Into the gas mixture, they sprayed tiny droplets of room-temperature water.
Upon closer inspection, they found that larger water droplets tended to have a positive charge, while smaller water droplets had a negative charge. Basic physics tells us that when oppositely charged droplets approach each other, tiny charges jump between them.
Although they are too fast to be seen under normal circumstances, researchers used high-speed cameras to capture the tiny flashes of light, confirming that the phenomenon does exist.
Importantly, in ancient atmospheric samples, just the spray of water was enough to ionize the air and trigger the formation of organic molecules with carbon-nitrogen bonds, such as hydrogen cyanide, glycine and uracil. These bonds are among the most common in organic chemistry, and the molecules in which they occur provide the building blocks of proteins and DNA.
"Given that lightning is an intermittent and unpredictable phenomenon, and water jets are very common on Earth, we believe our results provide another possible pathway for the abiotic formation of carbon-nitrogen bonds," the researchers wrote. "This means that waves, waterfalls, and other water jets may have stirred up large amounts of organic compounds on Earth, and these building blocks may have eventually begun to accumulate into the earliest life forms."
The research was published in the journal Science Advances.