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Fossils are rare things. Only a fraction of organisms get turned into stone. The vast majority of fossilized remains are hard tissues like bones, so finding things from the “squishy” bits of an organism is very unlikely. An even smaller fraction of fossils are from microscopic organisms. Given all this, a group of researchers have truly hit jackpot: the discovery of microfossils that hold the remains of ancient single-cell organisms that were alive roughly 1 billion years ago, preserved to such an incredible degree you can see the distinct cellular structures inside.
As reported in the journal Scientific Reports, the researchers analyzed material from the Cailleach Head Formation, in western Scotland. A billion years ago, this region was the bottom of an ancient lake. For whatever reason, these ancient cells died, and quickly after death certain solids in their organelles condensed, leaving an imprint of what they might have looked like.
Among the many microfossils discovered, the researchers found what looks to be a type of ancient organism known as Glenobotrydion aenigmatis, a cyanobacterium that has internal structures more or less spread out within the cell. Of the other organisms the researchers could identify, some look a bit like the spheroidal coccus bacteria, and one cell looks like it could be eukaryotic, which are cells that have a nucleus separated from the rest, like humans, plants, and fungi.
The team, led by the University of Western Australia, credit the exceptional preservation of these fossils to the presence of two rare earth element phosphate minerals, monazite and xenotime. These minerals precipitate and harden, fossilizing the cells and their insides. Other, older fossilized cells have been found before, but this discovery is the first reported instance of the incredibly preserved structure of inner cells thanks to rare earth element phosphates.
The scientists believe this preservation was possible because, due to local erosion and drainage, the lake they lived in had a higher concentration of these minerals. Geological evidence suggests that the lakes in the region that were present a billion years ago were supplied by large rivers with heavy sediment. Once in the lake, the elements were actively absorbed by these cells, otherwise, they wouldn't be found inside the intracellular inclusions.
The team believes that these findings have pushed open the envelope when it comes to understanding microorganisms that lived in the Precambrian epoch. They could provide clues about the biology of these beings and also the ecosystem they lived in. They offer us a brand-new window into the distant past.
