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Appearance of oxygen in the atmosphere of the Earth lead to proliferation of sulphur bacteria. Thus, two billion years ago, the first phosphorites came into being.
Tiny balls in rock dating back two billion years, visible under microscope only, helped Estonian scientists solve the mystery of how initial phosphate rock came to be. Turns out, it was decanted by bacteria dwelling at the bottom of the sea.
In Karelia, on the shores of Lake Onega, there lies a village called Shunga, close to which the earth lays bare two billion years old rock. After this very village, the carbon-rich rock shungite derives its name. In the same outcrop, Estonian scientists discovered one of the oldest layers of phosphorus-enriched sediment, on the basis of which they cast new light on how phosphorite was created.
Differently from Viru County phosphorite, about 490 million years old and resulting from sedimentation of shells of sea creatures, there has so far been no convincing theory about the origins the older layers in Karelia and elsewhere.
As revealed by geological research, the initial phosphorite layers the world over appeared at the same time, approximately two billion years ago. «Up to now, the big question was: why then? And why, geologically speaking, so suddenly?» explains Lauri Joosu, doctoral student at University of Tartu.
«Definitely, oxygen – appearing in the atmosphere a couple hundred million years before, played a role; is has been speculated that sedition of phosphorus had to have been influenced by living organisms; but how exactly, was not known,» says he.
Placing bits brought from Karelia under microscope, Mr Joosu saw – among other things – tiny balls, recognised by him and his colleagues as fossils of bacteria. Even today, such bacteria, which love sulphur and produce phosphorite, are dwelling en masse at Africa’s west coast, for instance.
The find and data gained by analysing the rock provide basis to claim that it was these very bacteria which served to decant phosphorus. «In our article, we suggest that, about two billion years ago, the Earth’s development initially produced environmental conditions suitable for proliferation of sulphur bacteria,» says Mr Joosu, for whom the research will provide core of Doctoral thesis.
«Phosphorus is a vital biological element, and contemporary circulation of phosphorus and creation of phosphorite are very closely linked to living nature,» he says. «In the article, we claim that at least two billion years ago, phosphorites appeared as impacted by bacteria, just as it is today.»
According to geologists, preconditions for it were laid by free oxygen first appearing in Earth’s atmosphere a couple of hundred million years before. «Oxygen enhanced erosion of rock outcrops, as a result of which more phosphorus was carried into bodies of water, thus enhancing growth of living organisms and conditions fitting for sulphur bacteria,» says Mr Joosu.
Also, it cannot be ruled out that the appearance of initial phosphorites was linked to hot water springs opening in bottom of seas due to volcanic activity, also providing for conditions favourable for said bacteria. The geologists hope to find confirmation to these suppositions, in cooperation with geochemists and biologists, by investigating increment cores of shungite gotten from boreholes drilled in cooperation of Tallinn University of Technology and Geology Institute of Karelia.
The research, compiled in cooperation of geologists of University of Tartu with colleagues from Russia, UK, Germany, France and Norway, was published this Sunday by the respectable science journal Nature Geoscience.