Life on Earth needs nitrogen.
It is an essential building block for proteins and DNA, helping all living things grow and function.
Even though nitrogen makes up most of our air, plants and animals cannot absorb it directly. Instead, tiny microbes convert nitrogen gas into a form that living organisms can use.
This process is called nitrogen fixation.
For a long time, scientists have wondered how nitrogen was made available for life billions of years ago.
Where did early life get its nitrogen? What role did it play in the development of living things?
A team of scientists, led by Dr. Michelle Gehringer from RPTU, has been working to answer these questions. Their research has now uncovered a new source of nitrogen that may have helped life thrive in Earth’s early oceans.
Dr. Gehringer and her team focused on how nitrogen-fixing microbes behave under different environmental conditions. They studied two forms of nitrogen: the lighter isotope 14N and the heavier isotope 15N.
Modern microbes use both in a specific ratio, and scientists measure this ratio by analyzing burned nitrogen-containing material.
Until now, researchers assumed that microbes kept the same 15N/14N ratio even under extreme conditions, such as an atmosphere with no oxygen and high levels of carbon dioxide—similar to early Earth.
However, no one had tested if this was true.
To find out, the team grew cyanobacteria (bacteria that can perform photosynthesis) under early Earth-like conditions. The results showed that their nitrogen ratio stayed the same. This suggests that nitrogen fixation has remained stable for billions of years, supporting the idea that microbes played a key role in making nitrogen available for life throughout Earth’s history.
The research didn’t stop there. Dr. Gehringer collaborated with Dr. Ashley Martin from Northumbria University and Dr. Eva Stüeken from the University of St Andrews to study ancient stromatolites. These are layered rocks formed by microbes and can provide clues about ancient ecosystems.
The scientists examined 2.7-billion-year-old stromatolites, grinding them into powder to analyze their nitrogen content. They expected to find signs of biological nitrogen fixation by cyanobacteria, similar to modern stromatolites. But they found something surprising: ancient stromatolites also contained nitrogen in the form of dissolved ammonium, which microbes could use as an additional nitrogen source.
Where did this ammonium come from? The most likely answer is deep-sea hydrothermal vents—hot underwater openings where mineral-rich fluids flow from the Earth’s crust. The team also studied volcanic basin rocks of the same age and found similar evidence of ammonium from hydrothermal activity. This means nitrogen was more widely available than previously thought, allowing life to spread and diversify in early Earth’s oceans.
For a long time, scientists believed that early life on Earth struggled due to a lack of usable nitrogen. This new discovery suggests otherwise—hydrothermal vents provided an extra nitrogen source, meaning life had more opportunities to grow and evolve in both deep and shallow waters.
What does this mean for life beyond Earth? Scientists know that Mars had hydrothermal activity in the past, and similar vents likely exist on icy moons like Europa and Enceladus. If nitrogen was available in these environments the way it was on early Earth, then life might have existed—or still exist—on other planets and moons.
This exciting research, published in Nature Communications, Applied and Environmental Microbiology, and Geology, sheds new light on how life began on Earth and where else in the universe it might be possible.
Source: KSR.
