Traces of sulfur bacteria in the sediment on the border between the Triassic and Jurassic periods confirmed that the saturation of the world ocean waters hydrogen sulfide was one of the causes of mass extinctions 201,6 million years ago, paleontologists claim in an article published in the journal Nature Geoscience.

The history of life on Earth consists of five major or mass extinctions, the ecent" of which, the Cretaceous-Paleogene, about 65,5 million years ago led to the death of the dinosaurs. Fourth extinction, Triassic-Jurassic, occurred about 201,6 million years ago and, in particular, led to the disappearance of about 50% of all the generations of the inhabitants of the land and ocean.

A group of scientists under the direction of the Bas van de Chatpage (Bas van de Schootbrugge) from the Goethe Institute in Frankfurt am main (Germany) studied marine sedimentary rocks formed during the Triassic-Jurassic extinction at the place of modern Germany and Luxembourg.

Scientists divided the fragments of rocks on the layers studied fossils inside them and had analysed the chemical composition of deposits. Most of Chatpage and his colleagues were interested in vibrations of oxygen in sea water, which occurred before and after the mass extinction.

For this paleontologists have calculated the proportion of isgenerating is a special light-sensitive pigment contained in the shells sulfur bacteria that live in the surface water layers. Such bacteria feed on hydrogen sulfide and not stand in the presence of oxygen in the water. Therefore, knowing the approximate concentration of isgenerating in the rock, you can learn the approximate chemical composition of sea water in bygone era.

According to the authors, sedimentary rocks formed to extinction, practically free of traces of pigment. This means that the proportion of hydrogen sulphide in the water of the world ocean at the end of the Triassic was minimal. On the other hand, the concentration of isgenerating gets dramatically increase when approaching the boundary of the Triassic and Jurassic period.

The increase in the share of this substance is accompanied by a decrease in the number of fossils shellfish, invertebrates and plankton. Most likely, this means that the waters were highly saturated with hydrogen sulphide and contained very little oxygen, which caused the extinction of the majority of living creatures. These findings are confirmed by a rather high level of organic nitrogen in sedimentary rocks - protein molecules from the tissues of dead animals had no time to rot due to low oxygen levels in the water and their bodies fell into the sediments on the ocean floor.

This event led to a kind of "revolution" among phytoplankton is dominant in the Triassic period dinoflagellates were ousted in the Jurassic era, the algae-Chloropidae able to live in water with low content of oxygen.

As noted by Chatpage and his colleagues, the composition of sea water during the Triassic-Jurassic and Permian-Triassic extinction was very similar. To date, the common cause of the Permian extinction is considered "ascent" magma to the surface in the region of Eastern Siberia, which caused the emission of huge amounts of CO2 and hydrogen sulphide in the atmosphere. It is quite possible that the same scenario was typical for disaster 201,6 million years ago, scientists conclude.