Deep-sea hydrothermal vents provide clues about the origin of life

Scientists have discovered inorganic nanostructures surrounding deep-ocean hydrothermal vents that closely resemble molecules essential for life. 

These self-organizing nanostructures act as selective ion channels, capable of generating energy that can be harnessed as electricity. 

The research was led by Ryuhei Nakamura at the RIKEN Center for Sustainable Resource Science (CSRS) in Japan and The Earth-Life Science Institute (ELSI) of Tokyo Institute of Technology.

The study not only advances understanding of how life may have originated but also holds potential for applications in industrial blue-energy harvesting.

Potential birthplaces of life

Hydrothermal vents, where seawater seeps deep into the Earth’s crust, gets heated by magma, and rises back to the ocean surface, have long been considered possible birthplaces of life on Earth. 

The rising hot water, rich in minerals absorbed deep in the Earth, interacts with cold seawater near the ocean floor, causing chemical reactions that form solid structures known as precipitates around the vents. 

Hydrothermal vents provide an ideal environment for life due to their stability, mineral richness, and energy sources. 

Life functions without life forms

Much of life on Earth relies on osmotic energy, created by ion gradients, or the difference in salt and proton concentrations, between the inside and outside of living cells.

Nakamura’s research team was particularly interested in serpentinite-hosted hydrothermal vents. These vents are known for having mineral precipitates with complex layered structures composed of metal oxides, hydroxides, and carbonates. 

“Unexpectedly, we discovered that osmotic energy conversion, a vital function in modern plant, animal, and microbial life, can occur abiotically in a geological environment,” Nakamura said.

Key discoveries in the Mariana Trench 

The key samples for this research were collected from the Shinkai Seep Field, located in the Pacific Ocean’s Mariana Trench at a depth of 5743 meters. 

The most important sample was an 84-cm-long piece, primarily composed of the mineral brucite. Using optical microscopes and micrometer-sized X-ray beams, the team found that the brucite crystals formed continuous columns, creating nano-channels for fluid to flow through the vent. 

Additionally, the researchers observed that the surface of the precipitate was electrically charged, with the size and direction of the charge – positive or negative – varying across the surface.

Behavior that mimics living cells

Given that structured nanopores with variable charges are a hallmark of osmotic energy conversion, the team tested whether this process was occurring naturally in the deep-sea rock. They used an electrode to measure the current-voltage relationship in the samples. 

When exposed to high concentrations of potassium chloride, the conductance was proportional to the salt concentration at the nanopores’ surface. 

However, at lower concentrations, the conductance remained constant, governed by the local electrical charge of the surface. This behavior closely mimics the voltage-gated ion channels found in living cells, such as neurons.

Spontaneous formation of ion channels

Testing the samples with the same chemical gradients found in the deep ocean, the researchers demonstrated that the nanopores functioned as selective ion channels. 

For example, nanopores with carbonate adhered to their surface allowed positive sodium ions to pass through, while those with calcium adhered to the surface only permitted negative chloride ions to flow.

“The spontaneous formation of ion channels discovered in deep-sea hydrothermal vents has direct implications for the origin of life on Earth and beyond,” said Nakamura. 

“In particular, our study shows how osmotic energy conversion, a vital function in modern life, can occur abiotically in a geological environment.”

Broader implications of the study

In industry, salinity gradients between seawater and freshwater are used to generate energy in a process called blue-energy harvesting. 

Nakamura believes that understanding how nanopore structures form spontaneously in hydrothermal vents could lead to improved synthetic methods for generating electrical energy from osmotic conversion, potentially advancing sustainable energy solutions.

“These findings open up an intriguing connection between the origin of life on Earth and beyond and the emerging field of chemistry and physics in nanospaces,” noted the study authors. 

“The current understanding of the material properties derived from confined nanospaces in geologic environments is still at an early stage, leaving much room for further exploration and discovery.”

The research is published in the journal Nature Communications.

Image Credit: NOAA

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