Ancient microbial rocks absorb carbon faster than forests

Along South Africa's coast, something unexpected is happening in plain sight. Microbialites—layered communities of microbes that build themselves into rock-like formations—are thriving in some of the harshest conditions on Earth. And they're doing something remarkable: absorbing carbon dioxide at rates that rival entire forests.

These "living rocks" aren't relics of deep time. Scientists studying four microbialite systems in southeastern South Africa discovered they're actively growing, expanding about two inches vertically every year. More striking, the team found these microbes absorb carbon at nearly the same rate during the day and at night—a discovery that upended what researchers thought they knew about how these ancient organisms work.

How They Absorb Carbon Around the Clock

Microbialites were long assumed to rely primarily on photosynthesis, meaning they'd absorb carbon only during daylight. But the research, published in Nature Communications, revealed something different. The microbes use photosynthesis during the day and switch to other metabolic processes at night—similar to how deep-sea vent microbes survive in darkness. This dual-mode carbon absorption is what makes them so efficient.

The numbers are striking. These microbialite systems absorb between 9 and 16 kilograms of carbon dioxide per square meter annually. To put that in perspective: an area the size of a tennis court would absorb as much carbon in a year as three acres of forest. That efficiency matters, especially since the carbon gets locked into stable mineral structures rather than stored as easily-degradable organic matter.

"The systems here are growing in some of the harshest and most variable conditions," said Dr. Rachel Sipler, a marine biogeochemist involved in the study. "They can dry out one day and grow the next. They have this incredible resiliency that was compelling to understand."

The research team conducted field expeditions over several years to examine these microbialite communities, which thrive in calcium-rich water seeping from coastal sand dunes. What they found contradicted textbook assumptions. These formations, long dismissed as nearly extinct relics, are alive and resilient—capable of rapid growth even when conditions swing wildly between dry and wet.

Why This Matters for Carbon Storage

Coastal marshes can absorb carbon at similar rates to microbialites, but there's a crucial difference. Carbon stored in marsh vegetation can break down and release back into the atmosphere. Carbon locked in microbialite minerals stays put—a more permanent form of sequestration. That stability could matter significantly if these systems are ever developed as part of climate strategies.

The researchers are now investigating how environmental factors and microbial variations influence carbon fate in different systems. Understanding these processes could eventually inform approaches to carbon sequestration in other environments. As Sipler reflected on the research: "If we had just looked at the metabolisms, we would have had one part of the story. If we had just looked at carbon uptake rates, we would have had a different story. It was through a combination of different approaches and strong scientific curiosity that we were able to build this complete story."

The next step is determining whether microbialites like these exist elsewhere and whether their carbon-absorbing capacity could be scaled or applied to climate challenges. For now, they remain a quiet reminder that some of Earth's most effective carbon solutions have been working away for billions of years—we just had to look closer.