Volcanoes May Have Kick-Started Life on Earth Four Billion Years Ago

Somehow, about four billion years ago, organic life sprang from a violent, oxygen-free Earth. The very first chemical building blocks of life emerged as volcanoes erupted and asteroids smashed into the planet.

Now, planetary scientists have found a class of molecules that could have brewed in waters sprinkled with chemicals from volcanic eruptions. These molecules, they believe, might have driven reactions that led to the first organic life. The research was published in the journal Astrobiology.

Back in 2015, scientists found a method to synthesize the forerunners of RNA—one of the key ingredients of cells. Chemists created a cocktail for this key element of life by using hydrogen cyanide, hydrogen sulfide and UV light.

It remained unclear whether Earth would have held great enough stocks of these ingredients to kick-start life. "What were conditions on early Earth like before life?" Sukrit Ranjan, one of the study's authors, asked in a statement. "Could the scenarios [chemists] invoke have actually happened? They don't know as much what the stage setting was."

Ranjan gave a talk in 2016 on the gases churned out by volcanoes on Mars that ignited the curiosity of chemists in the audience. An early, pre-life Earth would have had the same kinds of conditions, they realized.

"They took away from that [talk] that, on early Earth, you don't have much oxygen, but you do have sulfur dioxide from volcanism … As a consequence, you should have sulfites," Ranjan, a postdoctoral fellow at the Massachusetts Institute of Technology, recalled. Sulfites could have set the stage for the planet's early lifeforms.

This gave researchers a target: Just how much of this molecule was around on an early Earth?

A "titanic" amount of sulfites

Ranjan estimated how much volcanism was likely taking place around 3.9 billion years ago using the geological record. He then figured out roughly how much of different gases these erupting volcanoes would have been spewing out, working from models in the literature.

Finally, he estimated the volume of gases that would have dissolved into shallow lakes—the kinds of environments where early chemical lifeforms could spring up and thrive.

A new class of molecules

Volcanoes, Ranjan worked out, would have blasted enormous levels of sulfur dioxide and hydrogen sulfide into the sky. Hydrogen sulfide in particular would have dissolved into shallow reservoirs, producing "titanic" amounts of sulfites and bisulfites.

These compounds, researchers think, could be thought of as a new class of molecules—a class that was available on ancient Earth.

Early chemical experiments give support to sulfites and bisulfites as potentially life-brewing molecules. They have been shown to produce ribonucleotides, which are the building blocks of RNA, and related molecules far more quickly and in much greater volumes than hydrosulfide.

Although the research can't actually prove this is what happened on the early Earth, it does show how life could have fizzled from the hot, violent volcanic eruptions that exploded across the planet.

"In shallow lakes, we found these molecules would have been an inevitable part of the environment," Ranjan said. "Whether they were integral to the origin of life is something we're trying to work out."