[ Watch the Video: The Origins of Life on Earth ]
Brett Smith for redOrbit.com – Your Universe Online
By simulating a geologic precursor of cell metabolism, a team of British and American scientists have taken an important step toward understanding how life arose on Earth. Their work is published in a new paper in the journal Astrobiology.
“What we are trying to do is to bridge the gap between the geological processes of the early Earth and the emergence of biological life on this planet,” said study author Terry Kee, a chemist at the University of Leeds.
Widely supported theories posit that life emerged on Earth around hydrothermal vents on the ocean floor, which are rich in gases and minerals capable of supporting life without energy from the sun.
“Before biological life, one could say the early Earth had ‘geological life,’” Kee said. “It may seem unusual to consider geology, involving inanimate rocks and minerals, as being alive. But what is life?”
“Many people have failed to come up with a satisfactory answer to this question,” he added. “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 generate electrical energy via a ‘redox reaction,’ a reaction where one molecule is ‘reduced’ by gaining electrons and one molecule is ‘oxidized’ by losing electrons. Similar reactions occur during photosynthesis and cell respiration, a process in which electrical energy produced as sugars are oxidized into carbon dioxide and oxygen is reduced into water.
Similarly, the environment around hydrothermal vents can act as a fuel cell as electrical energy can be produced from redox reactions between hydrothermal fuels and oxidants in seawater. The newly published study is a proof-of-concept for this type of fuel cell, the study team said.
“Certain minerals could have driven geological redox reactions, later leading to a biological metabolism,” said study author Laura Barge from the NASA Astrobiology Institute. “We’re particularly interested in electrically conductive minerals containing iron and nickel that would have been common on the early Earth.”
For the study, the team replaced the conventional platinum catalysts in fuel cells with those made from geological minerals. Although the iron and nickel replacements are much less reactive than platinum, a small but noteworthy power output showed that these metals could still produce electricity in the fuel cell – and therefore catalyze redox reactions in hydrothermal vents billions of years ago on Earth.
The research team said their findings were a major step forward in understanding how life on Earth arose and if a related process could occur on other worlds.
“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,” Barge said. “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.”