“We were surprised because these tubes are clearly not the result of a geological process,” explained Professor Cees Passchier of Johannes Gutenberg University Mainz. These words sum up the enigma that has surrounded scientists venturing into Namibia, Oman, and Saudi Arabia’s desert environments. Encased in the marble and limestone outcrops of these dry lands are strange micro-burrows, possibly the handiwork of some unidentified type of microbial life.
The find, outlined in the Geomicrobiology Journal, has created a scientific puzzle. The formations, thin tubes that cut through the rock, baffle established geological processes, so researchers believe that they have a biological origin. The formations, roughly half a millimeter in diameter and up to three centimeters long, are lined with fine calcium carbonate powder, which is a product of microbial activity. “We don’t currently know whether this is a life form that has become extinct or is still alive somewhere,” Passchier said.
The areas in which these strange structures were discovered are now dry, but receive sporadic rain showers and thick coastal fog. This suggests a period when these places were more humid, and possibly a living habitat for such enigmatic microbes. The parallel orientation of the burrows indicates a collective action, the efforts of microbial colonies, not individual organisms. “The width of the tubes is much wider than a single cell,” wrote Passchier and his colleagues, meaning that the organisms divided as they used up the nutrients of the rock.
The chemical composition of the rock samples also strengthens the biological origin hypothesis. “As no known chemical or physical weathering mechanism can explain this phenomenon with the microstructural and geochemical observations presented here, and the micro-burrows form inside the host rock. We suggest that they are of biological origin,” stated Dr. Passchier. This inference is supported by the occurrence of a clean calcium carbonate powder finer than grains, the microbial remains’ by-product, within the burrows.
The mystery is further fueled when the possible identity of the organisms involved is taken into account. Although bacteria, fungi, and lichens have been found to thrive in extreme environments, the particular organism can’t be identified. Fungi were excluded because no digestive chemicals commonly excreted by them were present, and the burrows’ peculiarities minimize the possibility of cyanobacteria being involved. This has scientists wondering whether an entirely new type of life could have developed to survive the hostile environments of ancient desert landscapes.
The potential of this finding is immense. If these life forms once inhabited Earth, they may still be found in unknown or extreme ecosystems, even on other planets. “This form of life, of which we do not know whether it still exists, could be important for the global carbon cycle,” says Passchier. It poses fascinating questions about the capability of life to survive under extreme conditions and adapt, an issue that becomes more and more relevant as we venture into the possibilities of life beyond Earth.
The researchers hope their discoveries will inspire more research and the identification of such rock features globally. The potential that these microbes that eat limestone might have been involved in ancient carbon cycles means the existence of such microbes could have great importance for understanding the Earth’s past and the future of the environment. As we keep pushing the frontiers of life on this planet, the discovery of these ancient microbial tunnels is a reminder of the world’s rich and enigmatic past and challenges the scientific world to venture further into the unknown.
