Deep below Earth’s surface, rock and mineral formations lay hidden with a secret brilliance. Under a black light, the chemicals fossilized inside shine in sensible hues of pink, blue and green. Scientists are using these fluorescent features to grasp how the caves formed and the way life is supported in extreme environments, which can reveal how life could persist in faraway places, like Jupiter’s icy moon Europa.
The researchers will present their results on the spring meeting of the American Chemical Society (ACS).
Because it seems, the chemistry in South Dakota’s Wind Cave is probably going just like places like Europa — and easier to succeed in. Because of this astrobiologist Joshua Sebree, a professor on the University of Northern Iowa, ended up tons of of feet underground investigating the minerals and lifeforms in these dark, cold conditions.
“The aim of this project as a complete is to try to higher understand the chemistry happening underground that is telling us about how life might be supported,” he explains.
As Sebree and his students began to enterprise into latest areas of Wind Cave and other caves across the U.S., they mapped the rock formations, passages, streams and organisms they found. As they explored, they brought along their black lights (UV lights), too, to have a look at the minerals within the rocks.
Under the black light, certain areas of the caves appeared to transform into something otherworldly as portions of the encircling rocks shone in several hues. Due to impurities lodged inside the Earth tens of millions of years ago — chemistry fossils, almost — the hues corresponded with different concentrations and varieties of organic or inorganic compounds. These shining stones often indicated where water once carried minerals down from the surface.
“The partitions just looked completely blank and devoid of anything interesting,” says Sebree. “But then, after we turned on the black lights, what was once only a plain brown wall became a brilliant layer of fluorescent mineral that indicated where a pool of water was once 10,000 or 20,000 years ago.”
Typically, to grasp the chemical makeup of a cave feature, a rock sample is removed and brought back to the lab. But Sebree and his team collect the fluorescence spectra — which is sort of a fingerprint of the chemical makeup — of various surfaces using a conveyable spectrometer while on their expeditions. That way, they will take the data with them but leave the cave behind and intact.
Anna Van Der Weide, an undergraduate student on the university, has accompanied Sebree on a few of these explorations. Using the data collected during that fieldwork, she is constructing a publicly accessible inventory of fluorescence fingerprints to assist provide a further layer of data to the normal cave map and paint a more complete picture of its history and formation.
Additional undergraduate students have contributed to the study. Jacqueline Heggen is further exploring these caves as a simulated environment for astrobiological extremophiles; Jordan Holloway is developing an autonomous spectrometer to make measurement easier and even possible for future extraterrestrial missions; and Celia Langemo is studying biometrics to maintain explorers of utmost environments protected. These three students are also presenting their findings at ACS Spring 2025.
Doing science in a cave isn’t without its challenges. For instance, within the 48-degrees Fahrenheit (9-degrees Celsius) temperature of Minnesota’s Mystery Cave, the team needed to bury the spectrometer’s batteries in handwarmers to maintain them from dying. Other times, to succeed in an area of interest, the scientists needed to squeeze through spaces lower than a foot (30 centimeters) wide for tons of of feet, sometimes losing a shoe (or pants) in the method. Or, they’d need to stand knee-deep in freezing cave water to take a measurement, and hope that their instruments didn’t go for an accidental swim.
But despite these hurdles, the caves have revealed a wealth of data already. In Wind Cave, the team found that manganese-rich waters had carved out the cave and produced the striped zebra calcites inside, which glowed pink under black light. The calcites grew underground, fed by the manganese-rich water. Sebree believes that when these rocks shattered, since calcite is weaker than the limestone also comprising the cave, the calcite worked to expand the cave too. “It’s a really different cave forming mechanism than has previously been checked out before,” he says.
And the unique research conditions have provided a memorable experience to Van Der Weide. “It was really cool to see how you’ll be able to apply science out in the sphere and to find out how you function in those environments,” she concludes.
In the longer term, Sebree hopes to further confirm the accuracy of the fluorescence technique by comparing it to traditional, destructive techniques. He also wants to research the cave water that also fluoresces to grasp how life on Earth’s surface has affected life deep underground and, reconnecting to his astrobiological roots, understand how similar, mineral-rich water may support life within the far reaches of our solar system.
The research was funded by NASA and the Iowa Space Grant Consortium.
