Fossil bacteria found in 3.4 billion years old sandstone in Australia have been nourished by sulfur. Photo: David Wacey
Read aloud Scientists around the British Martin Brasier may have found remnants of the world's oldest living creatures: they come from western Australia from a rock formation that could have been a beach about 3.4 billion years ago. The researchers have identified the suspected bacteria primarily by using sulfur-containing crystals, which are located around the cell-like structures? Scientists believe this is a clear indication that the bacteria used their energy from the reduction of sulfur compounds. While there are some older finds that have been considered to be the oldest fossil cells for a while, for some of them there has been some reasonable doubt that the structures actually date back to biological organisms. In 2002, the paleontologist Martin Brasier caused a sensation in the scientific world: he doubted the previously established thesis, found in Australia, over three billion old fossils are the oldest known form of life. The Briton sees in the microscopic finds structures that were created by mineral processes, and split with this interpretation, the microbiologists in two camps.

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. display

David Wacey (University of Western Australia, Crawley) et al .: Nature Geoscience, doi: 10.1038 / NGEO1238 Marion Martin


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