A new study challenges one of the key theories surrounding the origin of life on Earth first put forward by Charles Darwin. He suggested life first arose in shallow pools of water.
However, researchers at University College London successfully created protocells in hot, alkaline seawater similar to the marine environments found near deep-sea hydrothermal vent features, suggesting that terrestrial life could have begun in the deepest parts of the world rather than the shallowest.
"There are multiple competing theories as to where and how life started. Underwater hydrothermal vents are among most promising locations for life's beginnings – our findings now add weight to that theory with solid experimental evidence," said the study's lead author, Nick Lane, in a statement.
Previous experiments tried unsuccessfully to form protocells, which are viewed as one of the key building blocks to the evolution of cell-based life. However, creating protocells from simple molecules that occur naturally was successful in cooler freshwater under tightly controlled experimental conditions that later fell apart when duplicated in environments similar to hydrothermal vents.
"Other experiments had all used a small number of molecule types, mostly with fatty acids of the same size, whereas in natural environments, you would expect to see a wider array of molecules,” said first author Sean Jordan.
Writing in Nature Ecology & Evolution, the authors note that they were able to create protocells that could self-assemble in environments that were similar to hydrothermal vents. In particular, heat, salt, and alkalinity did not impede their development but helped to spur it.
"In our experiments, we have created one of the essential components of life under conditions that are more reflective of ancient environments than many other laboratory studies," said Jordan. "We still don't know where life first formed, but our study shows that you cannot rule out the possibility of deep-sea hydrothermal vents."
Oceanic hydrothermal vents are found at locations around the world only recently accessible to humans through advanced technology. Such marine features are vents that spew out minerals from below the Earth’s crust. When they come into contact with the surrounding seawater, such minerals reacted to create a warm, nitrogen-rich environment characterized by “chimneys” built up through years of mineral deposits capable of oozing alkaline and acidic fluids. Altogether, the environment provides an energy that is ripe for interactions between hydrogen and carbon dioxide that can form more and more complex organic compounds.
As our knowledge of hydrothermal vent features in the deep ocean has expanded, researchers have largely accepted the notion that terrestrial life began in the very, very hot depths of the deepest parts of the oceans. But it’s not so cut and dried. A 2017 study revived Darwin’s original notion with proponents and opponents on both sides of the argument, particularly as hydrothermal vents have been observed on other planets in our Solar System.
"Space missions have found evidence that icy moons of Jupiter and Saturn might also have similarly alkaline hydrothermal vents in their seas. While we have never seen any evidence of life on those moons, if we want to find life on other planets or moons, studies like ours can help us decide where to look,” said Lane.