By creating protocells — seen as a key stepping stone to the development of cell-based life — in hot, alkaline seawater, a team of scientists from the Centre for Life’s Origins and Evolution at University College London and Birkbeck College has added to evidence that the origin of life could have been in deep-sea hydrothermal vents rather than shallow pools.

Deep under the Earth’s seas, there are vents where seawater comes into contact with minerals from the planet’s crust, reacting to create a warm, alkaline (high on the pH scale) environment containing hydrogen.

The process creates 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 originated in such underwater vents.

Scientists researching the origins of life have made great progress with experiments to recreate the early chemical processes in which basic cell formations would have developed.

The creation of protocells has been an important step, as they can be seen as 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.

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.

“There are multiple competing theories as to where and how life started,” said University College London’s Professor Nick Lane, lead author of the study.

“Underwater hydrothermal vents are among most promising locations for life’s beginnings — our findings now add weight to that theory with solid experimental evidence.”

“We identified a flaw in the previous work,” added University College London’s Dr. Sean Jordan, first author of the study.

“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 study, Professor Lane, Dr. Jordan and their colleagues tried creating protocells with a mixture of different fatty acids and fatty alcohols that had not previously been used.

They found that molecules with longer carbon chains needed heat in order to form themselves into a vesicle (protocell).

An alkaline solution helped the fledgling vesicles 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.

“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 findings appear in the journal Nature Ecology & Evolution.

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S.F. Jordan et al. Promotion of protocell self-assembly from mixed amphiphiles at the origin of life. Nat Ecol Evol, published online November 4, 2019; doi: 10.1038/s41559-019-1015-y