Early Life Fed on Organic Haze

A haze of atmospheric chemicals similar to those now found on Saturn's giant moon Titan might have been a major source of food for ancient life on Earth, a new study suggests.

Scientists have long been fascinated with Titan, which is shrouded by a murky orange atmosphere of smog-like chemicals created as sunlight interacts with methane high above the surface.

"This thick haze completely shrouds Titan, so all you can see in the photographs is orange," said Margaret Tolbert, a chemist at the University of Colorado at Boulder and a study co-author.

Tolbert's team wondered if similar chemicals might have formed in early Earth's atmosphere, which at various times also contained methane. So they mixed methane and carbon dioxide—a major constituent of the Earth's primordial atmosphere—in a reaction chamber and exposed it to simulated sunlight.

Researchers had previously thought that carbon dioxide—which is not present in Titan's atmosphere—would stifle the reactions that produce complex molecules.

Instead, Tolbert's team found that their simulated atmosphere produced a stew of organic chemicals.

"Contrary to the early predictions, you get more haze with carbon dioxide," she said. "You also get a richer broth of chemicals, including oxygen-containing molecules.

"They have more energy," she added. "Microorganisms can eat them, so they can be a food source."

In other words, the work suggests that Earth's early atmosphere may have been a veritable banquet for the earliest single-celled organisms.

Tolbert's team reports its findings this week in the journal the Proceedings of the National Academy of Sciences.