Lead: In 2018, researchers Hazel Barton of the University of Alabama and Lars Behrendt of Uppsala University discovered a bright green cyanobacterial coating deep in an alcove of Carlsbad Caverns, New Mexico. The microbes appear to photosynthesize using near-infrared light via rare pigments, despite the absence of visible light. Measurements showed near-infrared concentrations up to 695 times greater in the cave interior than at the cave mouth, and similar light-harvesting cyanobacteria were found across sampled caves in the park. The team says the find both rewrites assumptions about where photosynthesis can occur on Earth and could inform searches for life on exoplanets.
Key Takeaways
- Discovery year and team: Hazel Barton (University of Alabama) and Lars Behrendt (Uppsala University) first documented the bright green mats in 2018 deep inside Carlsbad Caverns.
- Unseen light source: The organisms rely on chlorophyll d and f to absorb near-infrared wavelengths that humans cannot see.
- Large near-IR gradient: Near-infrared levels measured in the darkest alcove reached values 695 times higher than at the cave mouth.
- Widespread occurrence: Additional sampling across Carlsbad Caverns National Park found similar cyanobacteria in every surveyed cave.
- Astrobiology relevance: The team proposes experiments to define the minimum light levels these microbes need, information intended to help guide exoplanet observations with instruments such as the James Webb Space Telescope.
- Potential biosignature link: Researchers note that oxygen produced by life is one of the few strong atmospheric indicators of biology, making these findings relevant for interpreting exoplanet atmospheres.
Background
Photosynthesis is typically associated with visible light and surface environments, so finding photosynthetic organisms deep underground challenges standard assumptions about energy budgets in isolated habitats. Cyanobacteria are ancient, versatile microbes that historically have shaped Earth’s atmosphere by producing oxygen, but most known species use chlorophyll a and b, which absorb visible light. Chlorophyll d and f are rarer pigments that extend light capture into the near-infrared, enabling energy harvesting where visible wavelengths are scarce or absent.
Carlsbad Caverns, a limestone cave system in southeastern New Mexico managed by the National Park Service, contains intricate passageways and isolated alcoves that shield interiors from surface light. Cave researchers and microbial ecologists study these environments to understand extremophile survival, nutrient cycling, and the limits of terrestrial habitability. The discovery aligns with growing interest in analogues for extraterrestrial environments where low or shifted-light spectra might support life.
Main Event
During a 2018 field expedition, Barton and Behrendt explored a remote alcove well off the public walkway in Carlsbad Caverns and encountered a conspicuous bright green coating on limestone walls. The color and texture prompted sampling and targeted spectral measurements to determine whether the biomass was photosynthetic. Laboratory and field analyses identified the pigments chlorophyll d and f, and spectrometers registered near-infrared intensities far above values at the cave entrance.
Quantitatively, the team recorded near-infrared concentrations as much as 695 times higher in the alcove than at the mouth of the cave. The densest cyanobacterial colonies coincided with the highest measured near-IR levels, suggesting a causal link between the shifted light environment and microbial abundance. The limestone surfaces appear to scatter and reflect near-infrared wavelengths internally, effectively channeling invisible light deeper into the cave system.
After the initial alcove find, the researchers sampled additional caves within Carlsbad Caverns National Park and report locating similar light-harvesting cyanobacteria in every cave sampled. The team has proposed follow-up laboratory and field experiments, including a suggested NASA-funded study, to determine the minimum photon flux and wavelength composition these organisms require to maintain photosynthesis and growth.
Analysis & Implications
The discovery forces a re-evaluation of energy sources that can sustain photosynthetic life in permanently dark or light-shifted environments. If chlorophyll variants permit viable carbon fixation under predominantly near-infrared illumination, then subsurface niches previously considered inhospitable may nonetheless support microbial communities. That broadened habitability window has implications for how scientists model biospheres on other worlds, especially planets orbiting stars with different spectral outputs.
Red dwarf stars, which constitute the majority of stars in the Milky Way, emit proportionally more near-infrared radiation than sun-like stars. If life elsewhere can evolve pigments analogous to chlorophyll d and f, then photosynthesis under red-dwarf illumination may be feasible and should be considered when selecting exoplanet targets and interpreting atmospheric data. However, translating terrestrial cave observations to planetary-scale habitability requires caution: planetary surfaces, atmospheres and geochemical cycles add complexity not present in a confined cave system.
From an astrobiology planning perspective, empirically defining the minimum light intensity and spectral mix needed for these cyanobacteria to survive would provide concrete thresholds for telescope sensitivity and target selection. A measured lower bound on usable photon flux would help determine which exoplanets could plausibly host oxygen-producing biospheres detectable with instruments like JWST or future observatories. Yet establishing those thresholds demands controlled experiments that isolate light as a limiting variable from nutrients, temperature and water availability.
Comparison & Data
| Location | Relative near-IR level | Cyanobacteria presence |
|---|---|---|
| Cave mouth | 1× (baseline) | Scarce/patchy |
| Deep alcove (remote) | 695× (measured peak) | Dense mats |
The table summarizes field-measured contrasts between the cave entrance and the deep alcove where the brightest cyanobacterial growth was observed. Researchers emphasize correlation between elevated near-infrared intensity and colony size across sampled sites. While the 695× figure represents peak measurements in the studied alcove, local variability and microtopography influence light scattering and biomass distribution. Additional quantitative sampling and calibrated radiometry are needed to generalize these values across the entire cave system.
Reactions & Quotes
Scientists and park managers reacted to the finding as both an ecological surprise and a useful astrobiology analogue. The cave team highlighted the age and isolation of the habitat as notable.
“We showed that not only do they live down there, but that they photosynthesize in a completely sheltered environment where they’ve probably been untouched for 49 million years.”
Lars Behrendt, microbial biologist, Uppsala University
Behrendt framed the discovery in terms of long-term isolation and evolutionary persistence, but the age estimate is subject to further verification (see Unconfirmed). Barton stressed the larger significance for detecting life on other worlds:
“There are very, very few ways that oxygen can be made in an atmosphere without life, so finding oxygen on an exoplanet would be a very strong marker for potential life.”
Hazel Barton, professor of geological sciences, University of Alabama
Barton linked the terrestrial observations to the search for exoplanet biosignatures, urging careful experimental work to translate cave photophysiology into practical telescope strategies.
Unconfirmed
- The claim that the alcove community has been “untouched for 49 million years” is an inference by the researchers and has not been independently dated in peer-reviewed work.
- Whether these cave cyanobacteria could produce planetary-scale atmospheric oxygen detectable from interstellar distances remains speculative and requires modeling beyond the cave context.
- The proposed NASA study to determine minimum light thresholds has been suggested by the team but had not been confirmed as funded or scheduled at the time of reporting.
Bottom Line
The discovery of near-infrared–driven photosynthesis in the dark interiors of Carlsbad Caverns expands the known ecological niches where light-dependent life can persist on Earth. By demonstrating that chlorophyll variants can support photosynthesis in environments devoid of visible light, the finding encourages scientists to broaden criteria when assessing habitability both on our planet and on exoplanets orbiting red dwarf stars.
Moving from an intriguing field observation to robust astrobiology guidance will require laboratory experiments that quantify minimal usable light fluxes, controlled studies of pigment efficiency, and careful planetary modeling. If follow-up work confirms low-light thresholds and demonstrates ecological sustainability, telescope search strategies and biosignature interpretation could shift to include worlds previously deemed marginal for photosynthetic life.
Sources
- Yahoo News (news aggregation reporting on the BBC account)
- BBC News (news report referenced by field team)
- Carlsbad Caverns National Park — National Park Service (official park information)
- James Webb Space Telescope — NASA (context on telescope capabilities)