Did biology begin with tiny bubbles?

Somehow, billions of years ago, a mix of organic molecules formed and started the chemical reactions that became life. In a new study, researchers in Germany propose that tiny air bubbles in water sloshing through volcanic rocks could have helped concentrate those molecules to start the process (Nat. Chem. 2019 DOI: 10.1038/s41557-019-0299-5).

Over 10 years ago, Dieter Braun’s group at Ludwig Maximilian University of Munich showed that polymers like DNA can move along a temperature gradient in a process called thermophoresis. As they studied the phenomenon further, the researchers wondered whether thermophoresis could help move prebiotic molecules around in the tiny channels in volcanic rocks, one of the locations where scientists think life may have started on Earth.

The researchers found that bubbles in liquid-filled microchannels, like those in volcanic rock, provide an air-water interface where biomolecules can accumulate. Braun compares it to the coffee-ring effect, in which particles congregate at the edge of a ring of coffee to leave a darker outline to the stain when the liquid evaporates.

To demonstrate this bubble effect, the researchers made tiny bubbles in a heated microfluidic chamber filled with water containing biomolecules like lipids, RNA, and DNA. Within 30 min, biomolecules accumulated on the outer surfaces of the bubbles or collected into cell-like vesicles. Concentrating molecules on the bubble surface also sped up reactions like the replication of RNA.

We can’t know what conditions existed when life started, Braun says. “We just focus on the mechanisms and look for clues.” The clues Braun and his team have found are completely novel, according to David Deamer, an expert in origin-of-life chemistry at the University of California, Santa Cruz. Deamer hopes the findings will “inspire others to investigate such conditions and advance our understanding of how life can begin.”

Braun agrees, saying he recently presented his work and other scientists immediately suggested other experiments. “We would be very happy if we can make something for really small molecules that shows open ended evolution, and shows in principle how it could have worked out,” he adds.