Fluorescent caves on Earth can teach us about extraterrestrial life

Deep underground, where sunlight never reaches, ancient minerals lie hidden within the rock – until illuminated by a black light. In that moment, once-drab walls blaze with color: pinks, blues, and greens glow from within. 

For scientists studying how life survives in extreme environments, these fluorescent clues may offer critical insights – not only into Earth’s history, but also into the potential for life on other worlds, like Jupiter’s moon Europa.

At the Spring 2025 meeting of the American Chemical Society (ACS), researchers led by astrobiologist Joshua Sebree from the University of Northern Iowa are presenting new findings about the chemical makeup of cave systems and what it can teach us about life in places humans have yet to reach.

Mineral fingerprints and ancient clues

Sebree and his students have explored caves across the U.S., including South Dakota’s Wind Cave and Minnesota’s Mystery Cave, mapping their twisting passages and hidden formations. 

As they worked, the researchers also scanned the cave walls with ultraviolet light, uncovering brilliant displays of fluorescence created by mineral impurities embedded in the rock over thousands of years. 

These luminous patches often mark where water once flowed or pooled, leaving behind chemical traces. What looks like an ordinary stone wall under normal light is transformed under UV. 

“The walls just looked completely blank and devoid of anything interesting,” Sebree said. 

“But then, when we turned on the black lights, what used to be just a plain brown wall turned into a bright layer of fluorescent mineral that indicated where a pool of water used to be 10,000 or 20,000 years ago.”

The glowing hues provide more than visual drama. They reveal distinct chemical compositions that help scientists understand how the cave formed and how it may have supported life. 

These “chemistry fossils” are collected not by breaking off rock samples, but through a non-destructive method: using a handheld spectrometer, the team gathers fluorescence spectra, essentially chemical fingerprints of the rock’s surface, right in the field.

Building a new type of cave map

Undergraduate student Anna Van Der Weide is building a public database of these spectral fingerprints, adding a new layer of chemical information to traditional cave maps.

This work could help paint a clearer picture of a cave’s formation and environmental history.

Other students are contributing to the broader project as well. Jacqueline Heggen is studying the caves as models for astrobiological research on extremophiles – organisms that live in extreme conditions. 

Jordan Holloway is developing an autonomous spectrometer that could be used in future missions to planets or moons.

Celia Langemo is researching biometric monitoring systems to help ensure the safety of scientists exploring harsh underground environments.

Glowing minerals and cave development 

The work is far from easy. At just 48 degrees Fahrenheit (9°C), caves like Minnesota’s Mystery Cave require extra planning to keep instruments functioning.

For instance, the experts had to bury the spectrometer’s batteries in hand-warmers to keep them from dying. 

Reaching areas of interest sometimes meant crawling through tunnels less than a foot wide for long distances or standing in freezing water while conducting measurements.

Despite these physical obstacles, the fieldwork has already revealed major insights. In Wind Cave, the team found that manganese-rich water had carved out the cave and created zebra-striped calcites – formations that glow pink under black light. 

These formations appear to have contributed to cave expansion by fracturing weaker rock, suggesting a previously overlooked mechanism of cave development.

“It’s a very different cave forming mechanism than has previously been looked at before,” Sebree explained.

A glimpse into other worlds

The bigger picture, though, reaches far beyond Earth. Because the chemistry in caves like Wind Cave may resemble conditions on icy moons such as Europa, Sebree’s research helps scientists imagine how life could survive in dark, isolated, mineral-rich environments far from the sun.

Looking ahead, Sebree hopes to confirm the accuracy of fluorescence mapping by comparing it to traditional, more invasive techniques.

He also wants to explore why some cave waters glow under UV light, which might help explain how life from Earth’s surface could influence ecosystems far underground.

Ultimately, Sebree’s work is driven by a larger question: if life can thrive in the deepest, coldest corners of our planet, what’s stopping it from doing the same in the outer reaches of our solar system?

“It was really cool to see how you can apply science out in the field and to learn how you function in those environments,” Van Der Weide said.

That blend of fieldwork, curiosity, and science may one day help uncover life in places no human has ever gone.

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