Scientists conducted their research in the hot springs of Yellowstone National Park, which is also home to the Grand Prismatic Spring pictured here. (Pandora Pictures/Shutterstock)

BOZEMAN, Mont. — Billions of years ago, Earth was unrecognizable. It was an oxygen-poor planet hostile to most modern life forms. Today, in the scalding waters of Yellowstone National Park’s geothermal springs, scientists have discovered microbes that might reveal how life survived those harsh early conditions. A new study from Montana State University shows how these ancient organisms adapted to an environment that mirrors our planet’s earliest days.

The Great Oxidation Event marked a pivotal moment in Earth’s history. Roughly 2.4 billion years ago, our planet’s atmosphere transformed from virtually no oxygen to containing significant amounts of this vital gas. Today’s atmosphere is about 20% oxygen, but historically, oxygen levels were so low they would have been almost undetectable by modern instruments. This dramatic shift reshaped life on Earth, but questions remained about how organisms survived during this transition.

The study, published in Nature Communications, revealed answers in an unlikely place—the superheated waters of Yellowstone’s hot springs. In these extreme environments, where temperatures reach 190 degrees Fahrenheit (88°C), modern microbes demonstrate survival strategies that may mirror those used by Earth’s earliest life forms.

The research team focused on two specific hot springs in Yellowstone’s Lower Geyser Basin: Conch and Octopus Springs. While these springs share many characteristics, they differ in one crucial aspect: their chemistry. Conch Spring contains high levels of dissolved sulfide and almost no oxygen, creating conditions similar to Earth’s early atmosphere. Octopus Spring has higher oxygen levels and very little sulfide, representing a more modern environment.

“When oxygen started to increase in the environment, these thermophiles were likely important in the origin of microbial life,” says study author William P. Inskeep, in a statement. “There was an evolution of organisms that utilized oxygen. Octopus has more oxygen, and sure enough, there’s more aerobic organisms there. These environments have different casts of characters.”

Within these springs, the researchers discovered remarkable structures called “streamers,” visible formations that resemble small kelp plants. These streamers attach to rocks and other surfaces within the springs, developing filaments that wave in the rapid currents. While these structures look similar in both springs, they host vastly different microbial communities.

In Conch Spring’s oxygen-poor environment, the researchers found a specialized community of just 3-4 different types of microbes. These organisms have evolved remarkable adaptations that allow them to survive with minimal oxygen, including specialized proteins called high-affinity oxygen reductases. These proteins can effectively capture and use oxygen even when it’s present in extremely low concentrations.

The situation in Octopus Spring reveals a different story. Its more oxygen-rich waters support approximately 15 different types of microorganisms, demonstrating how increased oxygen levels can promote biological diversity. These microbes have developed various strategies for energy production, taking advantage of the higher oxygen availability in their environment.

Despite their differences, both springs share three key microbial species: Thermocrinis, Pyrobaculum, and Caldipriscus. These ancient lineages show remarkable adaptability, altering their survival strategies based on available resources. By studying the genes these microbes express in different environments, researchers gained insights into how early life might have adapted as Earth’s atmosphere changed.

The research represents over two decades of scientific investigation in Yellowstone National Park. Montana State University’s location in the Greater Yellowstone Ecosystem provides unique opportunities for this research.

“It would be very difficult to reproduce this kind of an experiment in the laboratory; imagine trying to create hot-water streams with just the right amounts of oxygen and sulfide. And that’s what’s so nice about studying these environments. We can make these observations in the exact geochemical conditions that these organisms need to thrive,” says Inskeep, who has conducted research in Yellowstone since 1999.

These microorganisms’ ability to adapt to different oxygen levels demonstrates the remarkable flexibility of life. The research shows how organisms can develop various strategies to survive in challenging conditions, from using specialized proteins to forming complex communities.

The presence of similar microbial species in both springs, despite their different oxygen levels, suggests that early life forms might have possessed remarkable adaptability. This flexibility would have been crucial during the Great Oxidation Event, as organisms needed to adapt to increasing oxygen levels in Earth’s atmosphere.

“It may seem counterintuitive to understand complex life by studying something that’s simple, but that’s really how it has to start,” says study author Mensure Dlakić, an associate professor in the Department of Microbiology and Cell Biology. “You have to think back to understand where we are today.”

This research contributes to our understanding of how life evolves and adapts to environmental changes. While modern hot springs cannot perfectly replicate Earth’s ancient conditions, they provide valuable insights into the strategies that early life forms might have used to survive. These findings help piece together the complex puzzle of life’s evolution on Earth and may inform our search for life on other planets.