Scientists Reveal How Early Life Adapted to Rising Oxygen Levels on Earth

A team of researchers in the United States has made new discoveries about how some of Earth’s earliest life forms adjusted to an environment with increasing oxygen levels.

The study, conducted by scientists at Montana State University (MSU) and published in Nature Communications, provides insights into how ancient microbes evolved in extreme conditions, offering valuable clues about the origins of life on our planet. For over two decades, Professor Bill Inskeep from MSU’s Department of Land Resources and Environmental Sciences has been investigating microorganisms thriving in Yellowstone National Park’s hot springs. In this latest research, Inskeep and his colleague, Associate Professor Mensur Dlakic from the Department of Microbiology and Cell Biology, aimed to deepen their understanding of life’s evolution before and during the Great Oxidation Event. This transformative period, which occurred approximately 2.4 billion years ago, saw Earth's atmosphere shift from having almost no oxygen to the 20% oxygen levels we rely on today.

To explore this, the researchers studied microbes in two geothermal springs—Conch Spring and Octopus Spring—located in Yellowstone’s Lower Geyser Basin. These sites were selected because they share many similarities, except for one key difference: Conch Spring has higher oxygen levels than Octopus Spring. This contrast allowed the team to investigate microbial communities in both low- and high-oxygen environments.

Focusing on three types of thermophiles—heat-loving microbes—that inhabit both springs, the scientists examined how these organisms may have been among the first to adapt to the oxygen increase during the Great Oxidation Event. These microbes form ‘streamers,’ delicate, thread-like structures that sway in the flowing hot water, resembling tiny underwater plants. While streamers in both springs appeared similar, genetic analysis revealed that they hosted distinct microbial populations.

The researchers found that Octopus Spring, with its higher oxygen levels, supported a more diverse microbial ecosystem. “Octopus Spring contained around ten microbial populations that were absent in Conch Spring, including additional early-evolved bacteria and archaea,” Inskeep explained.

Genetic analysis further showed that microbes in the low-oxygen Conch Spring had highly active genes tailored for survival in oxygen-deficient conditions. In contrast, those in Octopus Spring exhibited genes adapted for oxygen-rich environments, suggesting that they evolved to thrive as atmospheric oxygen levels increased.

The findings from Inskeep and Dlakic’s study are helping scientists reconstruct how life adapted to Earth’s changing conditions over billions of years, with Yellowstone providing an ideal natural setting for such research. “Recreating these conditions in a lab would be extremely difficult,” Inskeep noted. “Trying to simulate hot-water streams with the right balance of oxygen and sulfur would be nearly impossible. That’s why studying these natural environments is so valuable—we can observe these organisms in precisely the geochemical conditions they require to survive.”

Though ancient microbes may seem unrelated to modern life, they provide crucial insights into how all living organisms, including humans, have adapted to survive over time. “It may seem counterintuitive to study something so simple to understand complex life,” Dlakic added, “but that’s where it all begins.”