Among the tricky carnivorous plants, great white shark-killing orca whales, and other remarkable flora and fauna that call South Africa home is a remarkable group of “living rocks.” Called microbialites, these communities are similar to coral reefs and are built up by microbes. These tiny living organisms absorb and release dissolved minerals into more solid rock-like forms. Microbialites are also some of the oldest evidence of life on Earth and can be found in layered, self-sustaining communities called microbial mats.  New research recently published in the journal Nature Communications also finds that these living rocks are not just surviving along South Africa’s coast. They’re thriving. The new study tallies how microbialites take carbon and turn it into fresh layers of calcium carbonate. These structures then use photosynthesis (the same way that plants use the sun to make food) and other chemical processes to absorb that carbon day and night at the same rate as the other microbes living within their microbial community. According to the study’s authors, the rate at which they use carbon shows the impressive efficiency of  these microbial mats, taking the dissolved carbon out of their environment and moving it off into a stable mineral deposit. “These ancient formations that the textbooks say are nearly extinct are alive and, in some cases, thriving in places you would not expect organisms to survive,” Dr. Rachel Sipler, a study co-author and a marine biogeochemist at Bigelow Laboratory for Ocean Sciences in Maine, said in a statement. “Instead of finding ancient, slow growing fossils, we’ve found that these structures are made up of robust microbial communities capable of growing quickly under challenging conditions.” Scientists have long struggled to understand how microbial communities like these interact with their environment. Part of the difficulty is that the data on these interactions comes from the fossilized remains of microbialites, some of which are billions of years old. Fortunately, living microbialites are still widely distributed in salty marine environments around the world. Sipler and the team also looked at the underlying geochemical processes at play. Over several years, they conducted multiple field expeditions, examining four microbialite systems in southeastern South Africa. Here, calcium-rich hard water seeps out of coastal sand dunes. “The systems here are growing in some of the harshest and most variable conditions,” Sipler said. “They can dry out one day and grow the next. They have this incredible resiliency that was compelling to understand.” A pool of water dominated by microbialites in South Africa’s Eastern Cape. Image: Rachel Sipler. They found that these systems were rapidly depositing the calcium carbonate, estimating that the structures can grow roughly two inches vertically every year. Surprisingly, they also found that the amount of carbon absorbed during day and night were roughly the same. Since these systems have long been thought to be driven by photosynthesis alone, the team was surprised to find that nighttime uptake rates are as high as during the day. After repeating their experiments several times, the team confirmed that the microbes are using metabolic processes other than photosynthesis to absorb all of that carbon in the absence of sunlight. This is similar to how microbes living in deep-sea vents are able to survive in near total darkness. Based on daily rates of carbon uptake, the team estimates that these microbialites can absorb the equivalent of about 20 to 25 pounds (nine to 16 kilograms) of carbon dioxide every year per square meter. That would be like an area the size of a tennis court absorbing as much carbon dioxide as three acres or forest every single year. This carbon-absorbing rate makes these microbial systems one of the most efficient biological mechanisms storing carbon long-term observed in nature. “We’re so trained to look for the expected. If we’re not careful, we’ll train ourselves to not see the unique characteristics that lead to true discovery,” Sipler said. “But we kept going out and kept digging into the data to confirm that the finding wasn’t an artifact of the data but an incredible discovery.” Additionally, coastal marshes are similar to these microbialites since they can take in carbon at a similar rate. However, marsh microbes put all of that energy into organic matter, which can be easily broken down compared to the more stable, mineral structures in microbialites. Given those differences, the team is investigating how environmental factors and variations in microbes may influence the fate of carbon in different microbial systems. “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,” Sipler said. “You never know what you’re going to find when you put people from different backgrounds with different perspectives into a new, interesting environment.” The post ‘Living rocks’ suck up a lot of carbon appeared first on Popular Science. ...read more read less