2.75 Billion-Year-Old Rocks Rewrite the Story of Earth’s Early Life

A study of ancient stromatolites reveals that ammonium reservoirs in early Earth’s oceans, likely influenced by volcanic activity, may have supported microbial life before the Great Oxidation Event.

Analysis of fossilized stromatolites dating back more than 2.5 billion years has shed new light on Earth’s environmental conditions before the emergence of oxygen.

A research team led by Dr. Ashley Martin of Northumbria University, in collaboration with experts in geology, microbiology, and geochemistry, examined ancient stromatolites preserved in southern Zimbabwe. Their study focused on understanding nitrogen cycling processes in early Earth’s ecosystems.

Nitrogen is essential for life but must first be converted into bioavailable forms as it moves through the atmosphere, soil, plants, and animals in the nitrogen cycle.

The team believes the unusual nitrogen isotope patterns found in Zimbabwe can offer new understandings of the mechanisms at play in Earth’s early marine environment before the Great Oxidation Event, which occurred between 2.5 to 2.3 billion years ago. This event, which was likely caused by the evolution of photosynthesis, is a major milestone in Earth’s history, and saw the first rise of oxygen concentration in Earth’s atmosphere.

Understanding Pre-Oxygen Earth

Scientists have long debated about the biological and chemical conditions that led to the Great Oxidation Event and little is known about nitrogen cycles before it took place. At this point in time, the early Earth would have looked very different from today, with most continents still submerged beneath a great ocean that covered the planet.

Dr. Martin, from the Department of Geography and Environmental Sciences at Northumbria University, said: “There are two key nutrients that control productivity in the oceans on geological timescales – nitrogen and phosphorus. Together they ultimately control the productivity of marine life.

“Our study reveals high nitrogen isotope values in 2.75 billion-year-old shallow water stromatolites, and lower nitrogen values in deeper marine sediments. This suggests that ammonium, which is nitrogen in its reduced form, accumulated in the deep waters and was brought into shallow waters by upwelling – the movement of deep nutrient-rich water toward the surface of the ocean.

“A large ammonium reservoir would have been very beneficial for early life, providing the nitrogen source needed for biological processes to occur. These conditions, likely in an ocean depleted of dissolved oxygen with a strong volcanic or hydrothermal influence, would have helped to support microbial growth, potentially spurring biological innovations and paving the way for the Great Oxidation Event.”

The Impact of Volcanic Activity on Early Life

A paper published in the prestigious scientific journal, Nature Communications, outlines the findings of the research team, which includes experts from the University of St Andrews; the University of Kaiserslautern-Landau in Germany; Leibniz University, Hannover; the Max Planck Institute for Chemistry in Germany and the University of Johannesburg in South Africa.

Dr. Eva Stüeken from the University of St Andrews explained: “We have long been puzzled by the unusual nitrogen isotope values in these rocks. Our new findings suggest a strong linkage to hydrothermal nutrient recycling, meaning that early life may in part have been fuelled by volcanic activity.”

Professor Axel Hofmann from the University of Johannesburg added: “Volcanism was exceptionally active 2.75-billion-years ago and left a lasting impact in the evolution of life at that time. Rocks in Zimbabwe preserve a remarkable record of this time interval.”

The proposal that in some areas of the world, large quantities of bioavailable nitrogen in the form of ammonium may have accumulated in the ancient oceans due to volcanic activity and fuelled the development of life, is supported by an earlier study from Dr. Martin, Dr. Stüeken and Dr. Michelle Gehringer from the University of Kaiserslautern-Landau.

Reference: “Anomalous δ15N values in the Neoarchean associated with an abundant supply of hydrothermal ammonium” by Ashley N. Martin, Eva E. Stüeken, Michelle M. Gehringer, Monika Markowska, Hubert Vonhof, Stefan Weyer and Axel Hofmann, 22 February 2025, Nature Communications.
DOI: 10.1038/s41467-025-57091-3

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