Catastrophic events, such as major volcanic eruptions, can wipe out all life in an area, leaving behind a blank slate. But since nature always finds a way back, researchers are increasingly curious about what that recovery actually looks like, starting at the microscopic level.
Understanding how bacteria first colonize a new area doesn't just tell us how plants and animals eventually return. It also provides clues about how life might have arisen on Earth in the first place, and how it might have arisen on other planets formed by volcanism.
To answer these questions, a team of scientists from the University of Arizona took advantage of a rare natural experiment: a series of eruptions of the Icelandic volcano Fagradalsfjall between 2021 and 2023. The researchers took samples of the lava flows almost immediately after they cooled, resulting in a study published in the journal Nature Communications Biology the first to closely track how microbes move into entirely new environments right as they form.
Study of lava opens window into early life
Volcanic eruptions provide researchers with something rarely found in nature: a truly barren starting point.
“The temperature of the lava coming out of the ground is over 2,000 degrees Fahrenheit, so it's obviously completely sterile,” said first author Nathan Headland, a graduate student at the University of Arizona's Lunar and Planetary Laboratory in press release. “It’s a blank slate that is essentially a natural laboratory to understand how microbes colonize it.”
Although previous research has examined how organisms restore damaged environments, most of these studies focus on plants and animals rather than microbes. Instead, this new work looks at the primordial succession at the microbial level, observing how life emerged as the habitat itself was still being formed. Unlike earlier studies in which the sample lava Several months after the eruption, Hadland's team collected material within hours of solidification.
They collected DNA from freshly formed lava, as well as from rainwater and airborne aerosols. Using advanced statistical and machine learning techniques, the team determined which organisms came first, how these tiny ecosystems evolved, and where the microbes originated.
Read more: Potential biosignatures on Mars could reflect ancient life in mineral-rich rocks
Fresh lava attracts hardy bacteria
Conditions for new lava flows are extreme. Although Iceland receives a lot of rain, freshly fallen lava contains little water and almost no organic nutrients. As a result, these places are among the lowest biomass environments on Earth, comparable to Antarctica or Chile's Atacama Desert.
Despite this, single-celled organisms populated the lava surprisingly quickly. Microbial diversity increased steadily during the first year after the eruption and then fell sharply after the first winter.
“It appears that the first colonizers are these 'cool' microbes, for lack of a better term,” Hadland said, “the ones that can survive in these initial conditions because there's not a lot of water and very little nutrients there.”
In subsequent months and seasonal shifts microbial community began to stabilize as additional organisms arrived with rainwater or spread from nearby areas. One of the most striking findings of the study was the enormous role rain played in shaping these early ecosystems.
“We see that most of the microbes come from rainwater, which is a pretty interesting result,” Hadland said.
Knowing that rainwater is not sterile because microbes can float freely in the atmosphere or cling to dust particles, the extent of seasonal changes surprised the team.
“To observe this huge shift after winter was quite surprising,” co-author and associate professor Solange Duhamel said in a press release, “and the fact that it was so reproducible and consistent across three different eruptions was something we did not expect.”
What does this mean for life beyond Earth?
“For the first time, we are beginning to gain a mechanistic understanding of how a biological community formed over time, from the very beginning,” Duhamel said. These ideas could spread far beyond Iceland.
Looking beyond our planet, we know that most of the surface of Mars is basaltic and formed volcanic processes similar to earthly. Although Martian volcanism has largely ceased, past eruptions may have created brief windows of habitability.
Understanding how microbes colonize fresh lava on Earth helps scientists predict how life might have arisen on Mars or any other planet and what biosignatures future missions should look for.
Read more: Powerful volcanoes could erupt more frequently across the planet as glaciers retreat
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