Just as many researchers had come to accept the idea that terrestrial life originated at hydrothermal vents in the ocean, new work by Ben Pearce of McMaster University in Canada and colleagues calls that hypothesis into question, and revives Darwin’s old idea of the origin of life in a warm little pond.
Computer modeling by the researchers suggests that the chemical building blocks of life were brought to Earth by meteorites and deposited in small bodies of water on the continents, where they readily assembled to form long-chained molecules such as RNA or DNA. This assembly would have occurred very fast—within a few cycles of the ponds drying out and becoming filled with water again. Thus, the resulting RNA or RNA-like molecules would likely have appeared very early in Earth’s history.
Since most of the meteoric infall of organic building blocks occurred prior to 4.17 billion years ago, the authors believe the first self-replicating RNA molecules (the so-called “RNA world”) would also have formed by that time—within 200 to 300 million years of Earth becoming habitable.
However, Pearce and colleagues leave the door open to a slightly different scenario. If early Earth was cold rather than warm, the wet-dry cycles could have been replaced with freeze-thaw cycles. These also would be well-suited for the assemblage of long-chained RNA molecules, but based on what we know of our planet’s evolution, a warm or hot early Earth seems more likely.
The new paper re-establishes the “warm pond” scenario as a leading explanation for the origin of life on Earth. This is, of course, one of the most important questions in astrobiology, because once we have pinned down where and how life originated, we can make much more informed scientific guesses about where life exists elsewhere. It’s also possible that both scenarios—ocean vents and warm ponds—are possible pathways for the origin of life on Earth. And there may be other scenarios we haven’t yet considered. New insights in this field are hard to come by, but we do advance, however slowly and incrementally.