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WWW.HZDR.DE discovered 02.15 TITLE UNDERGROUND: The red colored stone walls of Swedish research repository Äspö's tunnels penetrate around 500 meters into the granite. DIVERSITY: "Biofilms", which form a rusty brown ferrihydrite sludge, grow on the tunnel walls as well as in and around the watery crevices of Äspö. time can also tolerate high doses of radioactive radiation very well," reports Andrea Cherkouk, who also does research at the Institute of Resource Ecology of the HZDR. In addition to bacteria, such archaea constitute an important domain of life on Earth. Regardless of the host rock in which a nuclear repository is ultimately established, microorganisms can play an important role. And this of course makes the tiny creatures very interesting for repository researchers. So it is not surprising that these three scientists are currently actively involved in the recently launched MIND project of the European Union, which aims to take a closer look at life underground - and thus also in a repository. Fractures in granite A look at the geology of the underground environment of Äspö explains the origin of these microorganisms. The Scandinavian peninsula is comprised predominantly of granite rock that was formed as molten liquid magma gradually cooled below the Earth's surface and shrunk slightly as it solidified. Since granite took up less space than magma, crevices and fissures were formed. When the massive weight of thousands of meters of thick glaciers covered the land much later during the Ice Age, the underground landscape changed once more and additional cavities were opened. But these fissures and crevices are nothing more than channels through which water can circulate. Not only is water one of the elements essential to all life, but it is at the same time an ideal medium for transporting microorganisms in particular. Water acts as a conveyor, carrying organisms throughout the underground environs. Although it may take time, microorganisms can reach a great many places over the course of millions of years. Bacteria slime Life in the depths is anything but unique: And in fact, researchers have come across microorganisms in almost all of the places they have looked underground. "But we didn't expect to find the rock walls in Äspö covered with slimy layers of bacteria," Evelyn Krawczyk-Bärsch recalls. Such "biofilms" can contain a diverse community of microorganisms. Researchers often start off examining the little life forms living in there using microbiological methods.