Researchers at the University of Alberta report that they may have identified a missing piece in one of science’s biggest questions: how life first began on Earth.
Many scientists think life started deep on the ocean floor, near hydrothermal vents that release heat and mineral-rich fluids from beneath the crust. These environments could have supplied energy and raw materials for early chemistry. However, a major puzzle has remained. Without sunlight, how were essential nutrients, especially usable forms of carbon and nitrogen, produced in amounts sufficient to support the first living systems?
"Without sunlight, how were essential nutrients, especially usable forms of carbon and nitrogen, produced in amounts sufficient to support the first living systems?"
To investigate, Long Li and his colleagues in the Department of Earth and Atmospheric Sciences examined rock cores drilled about 200 meters into the oceanic crust in the South China Sea. Their analysis revealed signs of a process known as abiotic nitrogen reduction (ANR), in which minerals act as catalysts to convert nitrogen into chemically useful forms. The team concluded that this reaction likely generated nutrients needed for life to emerge.
One important product of this process is ammonium. Li explains that ammonium plays a central role in the abiotic synthesis of organic compounds, which are the molecular building blocks required for the development of the earliest life forms.
The study was conducted in partnership with researchers at the South China Institute of Oceanography and was published in Nature Communications.
Evidence from the Ocean Floor
“This definitely fills in the gap for the first-step reaction in the origin of life,” says Li. “People have searched for this reaction for a long time, but this is the first time we have convincing evidence to show it is occurring on Earth, and probably did occur on early Earth as well.”
"...minerals act as catalysts to convert nitrogen into chemically useful forms. The team concluded that this reaction likely generated nutrients needed for life to emerge."
Although ANR has been produced under controlled laboratory conditions, detecting it in natural ocean settings has been challenging.
According to the authors, modern biological activity alters nitrogen in seawater and sediments, making it difficult to separate abiotic signals from those created by living organisms. By studying deeply buried rock samples, the team was able to identify geochemical evidence consistent with a nonbiological nitrogen reduction process.
Implications for the Faint Young Sun Paradox
The findings may also help scientists address the “faint young sun paradox.” This long-standing problem asks how liquid water could have existed on early Earth when the young Sun emitted less energy. Climate models suggest that surface temperatures at the time should have been well below 0 C.
Despite those models, geological records show that liquid water was present at least 4.4 billion years ago. Li says this apparent contradiction can likely be explained by greenhouse gases such as carbon dioxide, methane, and ammonia, which would have trapped heat in the atmosphere. Hydrothermal vents on the seafloor may have helped generate these gases, contributing both to a warmer climate and to the chemistry needed for life.
Li adds that the strength of the evidence from the South China Sea suggests this reaction was not limited to a single location.
“We definitely need more evidence to show that. But since the conditions for ANR are common in both modern and ancient oceans, we reasonably speculate that this could happen globally over Earth’s history.”
