Mysterious deep-sea hydrothermal vents, where fissures in the sea floor allow the magma in the Earth’s mantle to heat trapped water to high temperatures before it is pumped back into the ocean from towering natural chimneys, provide ideal conditions for the origins of life, scientists believe.
An experiment replicating the hot, alkaline conditions found at the vents saw the successful creation of protocells – regarded as a vital basic building block for life.
The research, published in the journal Nature Ecology & Evolution, even suggests that heat and alkalinity might be not just useful but essential for spawning living things.
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“There are multiple competing theories as to where and how life started. Underwater hydrothermal vents are among the 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, professor of evolutionary biochemistry at UCL.
At the vents, seawater comes into contact with minerals from the planet’s crust, reacting to create a warm, alkaline environment containing hydrogen.
This process creates the mineral-rich chimneys with alkaline and acidic fluids, providing a source of energy that facilitates chemical reactions between hydrogen and carbon dioxide to form increasingly complex organic compounds.
Some of the world’s oldest fossils, discovered by a UCL-led team, originated at such underwater vents.
The researchers have also suggested the results of the experiment provide hope of finding life on other planets and moons where there are oceans and similar conditions.
Previous experiments to create protocells from naturally-occurring simple molecules – specifically, fatty acids – have succeeded in cool, fresh water, but only under very tightly controlled conditions, whereas the protocells have fallen apart in experiments in hydrothermal vent environments.
The protocells are essentially the most basic form of a cell, consisting of just a bilayer membrane around an aqueous solution – a cell with a defined boundary and inner compartment.
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The study’s first author, Dr Sean Jordan from UCL’s genetics, evolution and environment department, said he and his colleagues identified a flaw in the previous work: “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.”
For the new study, the research team tried creating protocells with a mixture of different fatty acids and fatty alcohols which had not previously been tested.
They found molecules with longer carbon chains required heat in order to form into a protocell structure. What’s more, an alkaline solution helped the fledgling protocells keep their electric charge. A saltwater environment also proved helpful, as the fat molecules banded together more tightly in a salty fluid, forming more stable vesicles.
For the first time, the researchers succeeded at creating self-assembling protocells in an environment similar to that of hydrothermal vents. They found the heat, alkalinity and salt did not impede the protocell formation, but actively assisted 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,” Dr Jordan said.
“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.”
The researchers also pointed out that deep-sea hydrothermal vents are not unique to Earth.
Professor Lane said: “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.”