Researchers have uncovered inorganic nanostructures near deep-ocean hydrothermal vents that closely resemble molecules essential for life as we know it. These nanostructures are self-organizing and function as selective ion channels, generating energy that can be converted into electricity. This discovery enhances our understanding of the origins of life and offers potential applications for industrial blue-energy harvesting.
Led by Ryuhei Nakamura from the RIKEN Center for Sustainable Resource Science (CSRS) in Japan and The Earth-Life Science Institute (ELSI) at Tokyo Institute of Technology, researchers have found inorganic nanostructures surrounding deep-ocean hydrothermal vents. Remarkably similar to life-sustaining molecules, these nanostructures organize themselves and serve as selective ion channels, producing energy that can be transformed into electricity. The results, published on September 25 in Nature Communications, not only deepen our knowledge of life’s beginnings but also suggest applications in industrial blue-energy harvesting.
When seawater seeps deep into the Earth through cracks in the ocean floor, it is heated by magma, then rises to the surface and is released back into the ocean through fissures known as hydrothermal vents. The heated water contains dissolved minerals acquired during its journey deep within the Earth, and when it encounters the cooler ocean water, chemical reactions cause mineral ions to precipitate, forming solid structures around the vent.
Hydrothermal vents are believed to be the cradle of life on Earth due to their stable, mineral-rich environment that provides essential energy sources. A significant portion of life on Earth relies on osmotic energy, produced by ion gradients—the differences in salt and proton concentrations—between the inside and outside of living cells. The researchers from RIKEN CSRS focused on serpentinite-hosted hydrothermal vents, which have complex layered mineral precipitates consisting of metal oxides, hydroxides, and carbonates. “Unexpectedly, we found that osmotic energy conversion, a crucial process in current plant, animal, and microbial life, can occur abiotically in a geological setting,” explains Nakamura.
The research involved samples from the Shinkai Seep Field, located in the Pacific Ocean’s Mariana Trench at a depth of 5,743 meters. A significant sample, measuring 84 cm, predominantly comprised brucite. Using optical microscopes and micrometer-sized X-ray scans, the team discovered that brucite crystals were arranged in continuous columns that functioned as nano-channels for the vent fluid. They observed that the surface of the precipitate was electrically charged, with varying sizes and polarities—positive or negative—distributed across the surface. Recognizing that structured nanopores exhibiting variable charge are essential for osmotic energy conversion, the researchers proceeded to investigate whether this process was naturally occurring in the inorganic rock from the deep sea.
The team used an electrode to measure the current-voltage characteristics of the samples. When exposed to high concentrations of potassium chloride, the electrical conductance was proportional to the salt concentration at the surface of the nanopores. However, at lower concentrations, the conductance remained constant and was influenced by the local electrical charge of the precipitate’s surface. This charge-regulated ion transport resembles the function of voltage-gated ion channels found in living cells, including neurons.
By testing the samples with chemical gradients typical of the deep ocean environment, the researchers demonstrated that the nanopores function as selective ion channels. For instance, at areas where carbonate adhered to the surface, the nanopores permitted positive sodium ions to flow through. In contrast, at nanopores with calcium on the surface, only negative chloride ions were allowed to pass.
“The spontaneous formation of ion channels discovered in deep-sea hydrothermal vents has profound implications for understanding the origin of life on Earth and potentially elsewhere,” states Nakamura. “Specifically, our research reveals how osmotic energy conversion, a key function in living organisms today, can occur abiotically in geological settings.”
Industrial power generation often harnesses salinity differences between seawater and river water for energy, a technique known as blue-energy harvesting. According to Nakamura, gaining insights into how nanopore structures form spontaneously in hydrothermal vents could aid engineers in developing improved synthetic methods for generating electrical energy from osmotic conversion.
