Researchers have developed a new approach to simulating in a laboratory some of the processes that may have led to the emergence of cell metabolism on Earth – a crucial biological function for all living organisms.
The research, which is published online today in the journal Astrobiology, could help scientists understand whether it is possible for life to have emerged in similar environments on other worlds.
Senior Faculty Dr. Marc M. Baum and Dr. John A. Moss from the Oak Crest Institute of Science in Pasadena, CA, co-authored the paper along with researchers from the NASA Astrobiology Institute ‘Icy Worlds’ team at the Jet Propulsion Laboratory (JPL) in Pasadena and the School of Chemistry and the Centre for Computational Fluid Dynamics at the University of Leeds in West Yorkshire, England.
“This research aims to fill some of the gaps between the geological processes of the early Earth and the emergence of biological life on this planet,” said Dr. Baum.
Hydrothermal vents, formed where subsurface fluids emerge into the deep ocean, form energy-rich habitats for life. Scientists have also proposed that hydrothermal vents could have kick-started the emergence of life, since these geological environments produce electrical energy and organic compounds.
“Before biological life, one could say the early Earth had ‘geological life’. It may seem unusual to consider geology, involving inanimate rocks and minerals, as being alive. But what is life?” said Dr. Terry Kee from the University of Leeds. “Many people have failed to come up with a satisfactory answer to this question. So what we have done instead is to look at what life does, and all life forms use the same chemical processes that occur in a fuel cell to generate their energy.”
Fuel cells, such as those used in cars, generate electrical energy from chemical energy by reacting fuels and oxidants. This is an example of a ‘redox reaction’, as one molecule loses electrons (is oxidized) and one molecule gains electrons (is reduced).
Similarly, photosynthesis in plants involves generating electrical energy from the reduction of carbon dioxide to sugars and the oxidation of water to molecular oxygen. Respiration in cells in the human body is the oxidation of sugars to carbon dioxide and the reduction of oxygen to water, with electrical energy produced in the reaction.
Certain geological environments, such as hydrothermal vents can be considered as ‘environmental fuel cells’, since electrical energy can be generated from redox reactions between hydrothermal fuels and seawater oxidants, such as oxygen. Indeed, last year researchers in Japan demonstrated that electrical power can be harnessed from these vents in a deep-sea experiment in Okinawa.
In the new study, the researchers, who were joined by a team of community college students from NASA’s JPL, have demonstrated a proof of concept for their fuel cell model of the emergence of cell metabolism on Earth. In the laboratories at the University of Leeds and NASA’s JPL, the team replaced traditional platinum catalysts in fuel cells and electrical experiments with those composed of geological minerals.
Dr. Laura Barge lead author of the paper, from the NASA Astrobiology Institute ‘Icy Worlds’ team at JPL and Visiting Associate at Oak Crest, said: “Certain minerals could have driven geological redox reactions, later leading to a biological metabolism. We’re particularly interested in electrically conductive minerals containing iron and nickel that would have been common on the early Earth.”
Iron and nickel generally have a different chemical reactivity from platinum, but a small but significant power output successfully demonstrated that these metals could still generate electricity in the fuel cell – and hence also act as catalysts for redox reactions within hydrothermal vents in the early Earth.
For now, the chemistry of how geological reactions driven by inanimate rocks and minerals evolved into biological metabolisms is still a black box. But with a laboratory-based model for simulating these processes, scientists have taken an important step forward to understanding the origin of life on this planet and whether a similar process could occur on other worlds.
Dr. Barge said: “These experiments simulate the electrical energy produced in geological systems, so we can also use this to simulate other planetary environments with liquid water, like Jupiter’s moon Europa or early Mars.
“With these techniques we could actually test whether any given hydrothermal system could produce enough energy to start life, or even, provide energetic habitats where life might still exist and could be detected by future missions.”