Tiny, water-filled pores in hot rocks on the sea floor may have served as nurseries for Earth’s earliest forms of life. Using recreations in the lab, a team of German researchers show that the natural temperature gradients found in those long, almost tunnel-like pores could have promoted processes crucial for fostering early life -- such as the ability to replicate and the emergence of nucleic acids (the NA in RNA and DNA). The findings were published in Nature Chemistry last week.
For life to begin on Earth, we needed simple biomolecules to form more complex structures that can replicate themselves and store hereditary information in some shape and form that’s chemically stable. This required amassing all the precursor molecules into one highly concentrated solution. But in the early oceans, these compounds were present in surprisingly low concentrations. "Life is fundamentally a thermodynamic non-equilibrium phenomenon,” says Dieter Braun of Ludwig-Maximilians-Universität München. “That is why the emergence of the first life-forms requires a local imbalance driven by an external energy source -- for example, by a temperature difference imposed from outside the system.”
Seafloor pore systems heated by volcanic activity on early Earth may have acted as reaction chambers for the synthesis of molecules carrying genetic information. “The key requirement is that the heat source be localized on one side of the elongated pore, so that the water on that side is significantly warmer than that on the other,” Braun explains in a news release. Once all the necessary conditions were provided, biomolecules washed into the pores become trapped and concentrated by the temperature gradient. Because charged molecules prefer to move from the warmer side to the cooler one, longer molecules in particular become securely trapped.
So, Braun’s team recreated such a setting with all the necessary conditions. They used tiny glass tubes to reconstruct the natural pores found in rocks, and then they heated the pore from one side. This allowed the water, which contained dissolved fragments of linear DNA, to percolate through. The long strands, they found, did become trapped within the pore.
Once detained, the nucleic acids had the right conditions for replicating. In the hot zone, double strands separated into their component strands within minutes, and these single strands are then transported back to the cold side by the flow along the pore. There, they encounter the biochemical precursors funneled in by a continuous inward flow, and the strands start acting as templates for the formation of complementary strands. Not only are the strands replicated, they’re also elongated when fragments of varying lengths are stitched together. When the nucleic acids pile up beyond the pore’s storage capacity, the replicated molecules go out and colonize nearby pore systems on the sea floor.