- REUTERS/Ognen Teofilovski
- Charles Darwin once theorized that the origin of life – known as abiogenesis – could have happened as precursor compounds came together in “warm little ponds.” A new study provides evidence for that theory, modeling how meteorites may have delivered compounds that could have led to the formation of RNA (a cousin of DNA) in ponds all over the Earth. Proponents of the other major life-origin story, the idea that life comes from hydrothermal vents deep in the ocean, are not convinced.
The biggest question about life is an obvious one, but the answer is hotly debated.
How did it all begin?
The most well-known of biologists, Charles Darwin, once theorized in a private letter to his friend Joseph Lee Hooker that life – the very first molecules of it – could have emerged from a “warm little pond” where some precursor components underwent a chemical reaction, creating compounds that would later develop into the forms of life as we know them today.
The other main theory is that life could have first emerged underwater at ultrahot hydrothermal vents, where cold seawater is heated to searing temperatures by volcanic activity deep in the ocean, providing enough energy to transform chemicals and other particles.
This week, the warm little ponds theory got a boost.
In a study published Monday in the journal Proceedings of the National Academy of Sciences, researchers wrote that they had mathematically modeled a way that meteorites, which smacked into early Earth far more regularly than they do now, could have delivered organic materials called nucleobases to warm little ponds all over the earth. These nucleobases would have served as the building blocks for RNA (a cousin of DNA), which many scientists think was the first sort of “life” to emerge, since it can both store information and help catalyze chemical reactions that would lead to the formation of other organic compounds.
Scientists say that for life to exist, molecules have to be able to trigger reactions that lead to the creation of new molecules. RNA has properties that could allow it to do that without already having complex proteins, which DNA requires for the replication process – a key argument for why RNA would come first.
The authors say their simulation is the first to model this origin story in such a complete way, helping demonstrate that the warm little pond story might be the correct one.
“No one’s actually run the calculation before. It’s pretty exciting,” Ben Pearce of McMaster University, lead author of the new study, said in a press release.
- B. K. D. Pearce
A model for life formation
Pearce and co-authors created a model of what the Earth looked like as the planet changed geologically in its early stages. All over the world, meteorites that hit the planet somewhere between 4.5 and 3.7 billion years ago could have delivered nucleobases to those warm little ponds, thousands of which could have been found all over early continents still emerging from the ocean.
During dry seasons, these ponds would shrink, bringing chemicals together; they’d expand during wet seasons. Wet and dry cycles help explain polymerization, the process by which compounds develop into chains or three-dimension structures, the authors wrote. The shrunken pools during dry cycles would bring compounds close together, allowing them to bond, which is one of the reasons they think that chemicals coming together in more open water near hydrothermal vents is a less plausible explanation.
But because of rapidly changing environmental conditions during these cycles, the authors believe RNA must have formed within a few years of meteorite impact. Otherwise, UV from sunlight during dry periods could have destroyed the compounds.
The authors think this happened at least 4.17 billion years ago, millions of years before we have clear evidence of life forming on the planet. That evidence dates to about 3.5 billion years ago – though another study this week also made the claim that life existed at least 3.95 billion years before now.
There are several reasons the authors believe this model could help solve the question of the origin of life, known as “abiogenesis.” Their model accounts for meteorites as the source material for the RNA precursors; it can help explain how some of the necessary reactions would have occurred; and they say their timeline fits with the early geologic conditions of the planet.
“Because there are so many inputs from so many different fields, it’s kind of amazing that it all hangs together. Each step led very naturally to the next,” said study co-author Ralph Pudritz in the release. “To have them all lead to a clear picture in the end is saying there’s something right about this.”
But the question is still far from solved.
“Yeah, that’s a possibility, but it’s certainly far, far, far from being the only possibility, and it’s far, far, far from being true,” Jan Amend, a geochemist at the University of Southern California who studies hydrothermal vents, told Newsweek.
Amend disagreed with the necessity of the wet-dry cycle, pointed out the meteorite impacts could have destroyed the precursor compounds, and said that even meteorites probably couldn’t have delivered the all the necessary materials.
Other scientists prefer the hydrothermal vent explanation because they believe it’s the only way there could have been sufficient energy for the life-forming reactions to occur.
This new study at least advances the warm pond theory, even if the question remains far from solved.
“Based on what we know about planet formation and the chemistry of the solar system, we have proposed a consistent scenario for the emergence of life on Earth. We have provided plausible physical and chemical information about the conditions under which life could have originated,” co-author Dmitry Semenov of the Max Planck Institute for Astronomy said in the news release. “Now it’s the experimentalists turn to find out how life could indeed have emerged under these very specific early conditions.”