Catastrophic events such as major volcanic eruptions can wipe out all life in an area, leaving behind a clean slate. But since nature always finds a way back, researchers are increasingly curious about what this recovery actually looks like, starting at the microscopic level.
Understanding how bacteria first colonize new lands not only tells us how plants and animals eventually return. They also provide clues about how life appeared on Earth in the first place, and how it could have arisen on other planets formed by volcanoes.
To answer these questions, a team of scientists from the University of Arizona took advantage of a rare natural experiment: a series of eruptions from the Fagradalsfjall volcano in Iceland between 2021 and 2023. The researchers took samples from the lava flows immediately after they cooled, making the study published in Nature Communications Biology The first to closely track how microbes move into an entirely new habitat as it forms.
Studying lava provides a window into early life
Volcanic eruptions provide something nature researchers rarely get: a truly infertile starting point.
“The lava coming out of the Earth is over 2,000 degrees Fahrenheit, so it’s clearly quite sterile,” said first author Nathan Hadland, a doctoral student at the University of Arizona’s Lunar and Planetary Laboratory. press release. “It’s a blank slate that essentially provides a natural laboratory for understanding how microbes colonize it.”
Although previous research has looked at how organisms recover from disturbed environments, most of those studies focus on plants and animals, not microbes. Instead, this new work looks at primary succession at the microbial level, observing the arrival of life while the habitat itself is still forming. Unlike previous studies that sampled lava months after the eruption, Hadland’s team collected the material within hours of solidification.
They collected DNA from fresh lava, along with rainwater and aerosols. Using advanced statistical and machine learning techniques, the team determined which organisms appeared first, how these tiny ecosystems evolved, and where microbes originated.
Read more: Possible biosignatures on Mars may reflect ancient life in mineral-rich rocks
Fresh lava invites hardy bacteria
Conditions on the new lava flows are extreme. Although Iceland receives a lot of rain, the newly accreted lava contains little water and almost no organic nutrients. As a result, these sites are among the lowest biomass environments on Earth, comparable to Antarctica or Chile’s Atacama Desert.
Despite this, single-celled organisms colonized the lava surprisingly quickly. Microbial diversity increased steadily during the first year after the eruption, then declined sharply after the first winter.
“The first colonizers seem to be these hardy microbes, for lack of a better term, that can survive in these initial conditions, because there’s not a lot of water, and there’s very few nutrients,” Hadland said.
Over the following months and seasonal shifts, the microbial community began to stabilize as additional organisms arrived via rainwater or spread from nearby areas. One of the most striking findings in the study was the large role that rain played in shaping these early ecosystems.
“We see that most of the microbes come from rainwater, which is a very interesting result,” Hadland said.
Knowing that rainwater is not sterile, and microbes can float freely in the atmosphere or ride on dust particles, the magnitude of seasonal changes surprised the team.
“Seeing this massive transformation after winter was absolutely amazing, and the fact that it was repeatable and consistent across the three different eruptions — we didn’t expect that,” co-author and assistant professor Solange Duhamel said in the statement.
What does it mean for life outside Earth?
“For the first time, we are beginning to gain a mechanistic understanding of how a biological community emerged over time, right from the beginning,” Duhamel said. These ideas could extend beyond Iceland.
Looking beyond our planet, we know that much of Mars’ surface is basalt and formed by volcanic processes similar to those that occur on Earth. Although Martian volcanic activity has largely ceased, previous eruptions may have created short-lived windows of habitability.
Understanding how microbes colonize fresh lava on Earth helps scientists predict how life might appear on Mars or any other planet, and what biosignatures future missions should look for.
Read more: As glaciers retreat, powerful volcanoes may erupt more frequently across the planet
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