Rocks reveal the turning point when oxygen changed Earth forever
Several moments in Earth’s distant past help answer two fundamental questions: How did we get here? And where are we headed? These turning points reveal how life adapts to environmental changes.
One event, known as the Great Oxidation Event (GOE), was especially significant. Over two billion years ago, oxygen began to accumulate in the atmosphere for the first time. This shift made complex life, including humans, possible.
The Earth before oxygen
Before the GOE, Earth’s environment was almost completely anoxic – lacking oxygen. Life was limited to anaerobic organisms that thrived without it, relying on fermentation to survive.
Even today, similar life forms inhabit extreme places like acidic hot springs and deep-sea hydrothermal vents.
The GOE triggered a dramatic change. It transformed Earth from a planet devoid of atmospheric oxygen into one capable of supporting the diverse biosphere we know.
Scientists have long sought to understand exactly when and how this shift happened. In a recent study, researchers from Syracuse University and MIT uncovered new clues by examining ancient rock cores from South Africa.
The research provides a clearer timeline of how rising oxygen levels fueled biological evolution and paved the way for the first eukaryotes – organisms with complex cells.
Digging into the deep past
The team analyzed sedimentary rocks that are between 2.2 and 2.5 billion years old. These rocks, collected from carefully chosen sites in South Africa, preserve chemical evidence from the time of the GOE.
By studying stable isotopes embedded in these rocks, the researchers found signs of nitrate, a chemical marker that suggests more oxygen was present in ancient oceans.
The study was led by Benjamin Uveges, who earned his Ph.D. at Syracuse University and later completed the project as a postdoctoral associate at MIT.
Uveges collaborated closely with Christopher Junium, an associate professor of Earth and environmental sciences at Syracuse University, whose lab focuses on reconstructing past environmental conditions. The chemical analyses were performed using state-of-the-art instruments housed at Syracuse.
“The rocks that we analyzed for this study had very low nitrogen concentrations in them, too low to measure with the traditional instrumentation used for this work,” said Uveges.
“Chris has built one of only a handful of instruments in the world that can measure nitrogen isotope ratios in samples with 100 to 1,000 times less nitrogen in them than the typical minimum.”
How the research was conducted
In the lab, the team used an Isotope Ratio Mass Spectrometer (IRMS) to examine the nitrogen isotopes. First, they crushed the rock samples into powder and chemically treated them to extract specific elements.
The material was then turned into gas, ionized, and separated based on mass. Measuring the ratio of nitrogen isotopes – ¹⁵N to ¹⁴N – helped reveal how microbes processed nitrogen long ago.
A key part of the IRMS is the cryotrapping/capillary-focusing module, which allowed for precise measurements even with extremely low nitrogen levels. The equipment is one of only a few of its kind and plays a vital role in studies like this.
Decoding Earth’s oxygen timeline
But how does nitrogen unlock secrets about ancient oxygen levels? Microbes left chemical signatures in sediments that later hardened into rock. These signatures preserve a record of how nitrogen was cycled in ancient oceans.
By tracing changes in nitrogen isotope ratios, scientists can reconstruct how oxygen levels shifted over time.
The team’s findings suggest that aerobic nitrogen cycling started about 100 million years earlier than previously thought. This means oxygen-sensitive processes in the oceans were already happening long before oxygen accumulated in the atmosphere.
“All of this fits with the emerging idea that the GOE was a protracted ordeal where organisms had to find the balance between taking advantage of the energy gains of oxygenic photosynthesis, and the gradual adaptations to dealing with its byproduct, oxygen,” said Junium.
The rise of oxygen on Earth
The slow rise in oxygen levels set off a cascade of changes. As oxygen began to build up in the atmosphere, many anaerobic organisms were driven to extinction. In their place, organisms capable of using oxygen for respiration began to thrive.
This process, aerobic respiration, provides the energy needed for complex life processes such as muscle movement, brain function, and cell maintenance.
“For the first 2 plus billion years of Earth’s history there was exceedingly little free oxygen in the oceans or atmosphere,” said Uveges. “In contrast, today oxygen makes up one fifth of our atmosphere and essentially all complex multicellular life as we know it relies on it for respiration.”
“So, in a way, studying the rise of oxygen and its chemical, geological and biological impacts is really studying how the planet and life co-evolved to arrive at the current situation.”
A new chapter in Earth’s story
These results reshape how we understand Earth’s oxygenation. They show that the journey toward an oxygen-rich atmosphere – and the complex life it enabled – was even slower and more intricate than once believed.
“I hope our findings will inspire more research into this fascinating time period,” said Uveges. “By applying new geochemical techniques to the rock cores we studied, we can build an even more detailed picture of the GOE and its impact on life on Earth.”
The research gives us a clearer view of how life and Earth’s environment have shaped each other through deep time. It’s a reminder that big changes don’t happen overnight – and that the air we breathe today is the result of billions of years of slow, steady transformation.
The full study was published in the journal Proceedings of the National Academy of Sciences.
Image Credit: Benjamin Uveges
—–
Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates.
Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.
—–
