Now Brasier, who works at the University of Oxford, substantiates his thesis with new research results. Exploring one of the oldest rock formations in the world, the Strelley Pool Formation in western Australia, Brasier's team has now discovered structures that actually point to bacterial cells. Above all, the shape and structure of the approximately 3.4 billion years old fossils are similar to those of today's known bacteria: In contrast to inorganic structures, the putative cell walls are all the same thickness, and also the shape of the individual cells? determined via 3D recordings? fits into the picture. The carbon content and the type of cell colonies in the form of lumps and chains are also characteristic of bacteria. The most important indicator of microbial life, however, the scientists see in tiny iron sulfide crystals, popularly known as cat's gold. These pyrite crystals are located in and around the cells. For the researchers a clear indication of the energy production from sulfur? In their view, the bacteria reduced sulfates to sulfide, ie hydrogen sulfide and its salts. Bacteria using this energy source are still alive today? like her primitive relatives? a few inches below the surface of sandy beaches, forming a thin black carpet there.
The use of sulfur compounds to generate energy in the early bacteria, however, is a surprise, because researchers have long assumed that the first living beings lived photosynthetically. But during the lifetime of the bacteria studied, the earth was still hotter than today: the volcanic activity was significantly stronger, there were no continents, only islands, and the ocean had a temperature of 40 to 50 degrees Celsius. Algae and plants that produced oxygen did not exist yet. For this reason, the tiny fossils are probably also relatively well preserved? the oxygen-poor environment ensured its existence.
The Belgian paleo-biologist Emmanuelle Javaux sees the approach of focusing on the processes of organisms as a suitable method for detecting microbial life. "It actually seems to be true microorganisms." But she also gives concern: "The future will show if this assumption is true.? In any case, she sees in the process a way to identify similar life forms, for example, on Mars. Comparable finds on the earth are rather unlikely, since such old sedimentary rock is extremely rare. displayDavid Wacey (University of Western Australia, Crawley) et al .: Nature Geoscience, doi: 10.1038 / NGEO1238 Marion Martin