Along the coast of South Africa, strange rocky formations quietly grow in places where life seems unlikely to survive.
These structures, known as microbialites, look like ordinary rocks, but they are very much alive.
Built layer by layer by communities of microbes, they are some of the closest living relatives of Earth’s earliest ecosystems—and new research shows they are far more active and resilient than scientists once believed.
A new study co-led by researchers at Bigelow Laboratory for Ocean Sciences and Rhodes University reveals that South Africa’s coastal microbialites are not just surviving in harsh conditions.
They are growing rapidly and pulling large amounts of carbon out of their environment, locking it away in solid rock. The findings were published in Nature Communications.
Microbialites form when microbes absorb dissolved carbon from water and turn it into calcium carbonate, the same mineral found in limestone and coral reefs.
Over time, this process creates layered rock-like structures that can last for thousands—or even billions—of years.
Fossilized microbialites provide some of the oldest evidence of life on Earth, dating back more than three billion years.
Because most microbialites known to science are ancient fossils, researchers long assumed that living examples grow extremely slowly.
The new study challenges that idea. By studying four active microbialite systems along South Africa’s southeastern coast, scientists found that these “living rocks” can grow nearly two inches vertically every year.
“These formations are often described in textbooks as nearly extinct,” said lead author Rachel Sipler, a senior research scientist at Bigelow Laboratory. “Instead, we found vibrant microbial communities that are growing quickly in places with extreme and constantly changing conditions.”
The microbialites examined in the study form where calcium-rich water seeps out of coastal sand dunes. These environments are tough. The structures can dry out one day, be submerged the next, and face dramatic changes in temperature, sunlight, and water chemistry. Yet the microbes adapt with remarkable efficiency.
One of the most surprising discoveries was how these systems take up carbon. During the day, microbes use photosynthesis, much like plants, to absorb carbon dioxide. But the researchers found that carbon uptake continues at nearly the same rate at night, when there is no sunlight.
This nighttime activity shows that the microbes rely on additional chemical processes, similar to those used by organisms living around deep-sea hydrothermal vents. These alternative metabolisms allow the microbialites to keep growing around the clock.
By measuring daily carbon uptake, the team estimated that each square meter of microbialite can absorb the equivalent of nine to 16 kilograms of carbon dioxide per year. Scaled up, a microbialite area the size of a tennis court could capture as much carbon annually as several acres of forest.
What makes this even more significant is how the carbon is stored. Unlike plants and soils, which store carbon in organic material that can break down over time, microbialites convert carbon into stable mineral rock. This makes them one of the most effective natural systems for long-term carbon storage known.
The researchers also linked carbon uptake rates to the genetic makeup of the microbial communities for the first time. This connection helps explain why some microbialite systems grow faster than others and how different microbes influence the fate of carbon.
The team is now comparing microbialites with other carbon-absorbing ecosystems, such as coastal marshes. While marshes can take in similar amounts of carbon, they store it in softer organic matter rather than durable rock.
By combining fieldwork, chemistry, genetics, and ecology, the researchers were able to build a much more complete picture of how these living rocks function. Their work shows that even ancient forms of life can still surprise us—and may offer valuable clues about both Earth’s early history and future approaches to carbon storage.
As Sipler put it, curiosity and collaboration were key. When scientists look beyond expectations and bring different perspectives together, even rocks can turn out to be full of life.
