How Life Emerged on Early Earth: New Study Challenges Nitrogen Limitation Assumptions
by Robert Schreiber
Berlin, Germany (SPX) Mar 01, 2025
Researchers from RPTU University Kaiserslautern-Landau in Southwestern Germany are shedding new light on how life might have developed on early Earth. Their latest findings challenge long-standing theories that biologically available nitrogen was a limiting factor in early life’s expansion.
Nitrogen is a crucial component of proteins and other biological molecules. Although Earth’s atmosphere is rich in nitrogen, most organisms, including humans and most plants, cannot absorb it directly. Instead, nitrogen-fixing microbes convert atmospheric nitrogen into bioavailable forms. This process was equally essential billions of years ago, but scientists have long debated how effectively early life forms could access nitrogen.
Unraveling Ancient Nitrogen Sources
Dr. Michelle Gehringer, a geomicrobiologist at RPTU, is leading efforts to answer key questions about early Earth’s nitrogen sources and their role in life’s evolution. Her team recently validated a measurement method that demonstrates biological nitrogen fixation remains stable even under varying atmospheric conditions.
Nitrogen exists in two stable isotopes, 15N and 14N. “Nitrogen gas is a mixture of the light atom 14N and the heavier atom 15N. When modern microbes use nitrogen, they do so in a consistent ratio of these isotopes. We measure this by burning nitrogen-containing biomass and analyzing the nitrogen gas produced,” explained Gehringer.
Previous assumptions held that nitrogen-fixing microbes maintained the same 15N/14N ratio across different environmental conditions. However, this had never been experimentally verified. Gehringer’s team cultivated cyanobacteria under conditions similar to early Earth-oxygen-free and with high carbon dioxide levels. Their results confirmed that the 15N/14N ratio remains stable, reinforcing the idea that this ratio has been consistent throughout Earth’s history.
The Role of Hydrothermal Vents in Nitrogen Absorption
Building on these findings, Gehringer collaborated with Dr. Ashley Martin from Northumbria University, UK, and Dr. Eva Stueken from the University of St Andrews, UK, to investigate nitrogen cycles in 2.7-billion-year-old stromatolites-sedimentary structures formed by microbial activity. By grinding pristine, unweathered samples into fine powder for isotope analysis, the researchers discovered that ancient stromatolites incorporated nitrogen not only through biological fixation but also through dissolved ammonium.
“The most plausible source of this ammonium is hydrothermal activity on the sea floor,” noted Gehringer. The team also examined sedimentary rocks from a volcanic basin of similar age, further confirming the significance of ammonium from hydrothermal sources.
Implications for Early Life and Astrobiology
“It was previously thought that life on early Earth was constrained by nitrogen scarcity before atmospheric oxygen became abundant. However, our findings show that hydrothermal vents provided an additional nitrogen source, allowing life to thrive in both deep and shallow marine environments,” Gehringer said. This contributed to the emergence of microbial diversity that persists today.
The study’s implications extend beyond Earth. “Hydrothermal activity has been identified on Mars and likely occurs on icy moons in the outer solar system,” Gehringer added. This raises the possibility that similar nitrogen-enabling processes could support extraterrestrial life.
Research Report:Anomalous d15N values in the Neoarchean associated with an abundant supply of hydrothermal ammonium
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