Traces of sulfur bacteria in sediments at the boundary between the Triassic and Jurassic periods confirmed that the saturation of the World Ocean sulfide was one of the reasons for the mass extinction 201.6 million years ago, paleontologists say in a paper published in the journal Nature Geoscience.
The history of life on Earth has five major or mass extinctions, the most "recent" of which, Cretaceous-Paleogene, about 65.5 million years ago led to the death of the dinosaurs. Fourth extinction, Triassic-Jurassic, there was approximately 201.6 million years ago and, in particular, has led to the disappearance of 50% of all inhabitants of the land and labor of the ocean.
A team led by Bas van de Shotbryuge (Bas van de Schootbrugge) of the Goethe Institute in Frankfurt am Main (Germany) studied the marine sedimentary rocks formed during the Triassic-Jurassic extinction at the site of modern Germany and Luxembourg.
Scientists are divided into layers of rock fragments, studied fossils in them and analyzed the chemical composition of the sediment. Most Shotbryuge and his colleagues were interested in fluctuations of oxygen in sea water, which took place before and after the mass extinction.
To do this, paleontologists calculated izorenieratana share — a special light-sensitive pigment contained in the shells of sulfur bacteria that live in the surface layers of water. These bacteria feed on hydrogen sulfide and can not tolerate the presence of oxygen in the water. Thus, knowing the approximate concentration izorenieratana the rock, you can see the approximate chemical composition of sea water in the bygone era.
According to the authors, sedimentary rock formed to extinction, almost did not contain traces of pigment. This means that the fraction of hydrogen sulfide in the water of the world ocean in the late Triassic was minimal. On the other hand, the concentration izorenieratana begins to rise sharply near the boundary of the Triassic and Jurassic.
Increasing the proportion of this material is accompanied by a decrease in the number of fossils of mollusks, invertebrates and plankton. Rather, it means that the ocean waters were heavily saturated with hydrogen sulfide and contained very little oxygen, which caused the extinction of most living creatures. These conclusions are supported by a sufficiently high level of organic nitrogen in sediments — protein molecules from the tissues of dead animals just do not have time to decay because of the low oxygen levels in the water and the remains fell into the sediments on the ocean floor.
This event led to a kind of "revolution" of phytoplankton — dominate the Triassic dinoflagellates were ousted in the Jurassic period vodroslyami-chlorophytes, able to exist in water with low oxygen content.
According Shotbryuge and his colleagues, the composition of seawater during the Triassic-Jurassic and Permian-Triassic extinction was very similar. To date, the common cause of Permian extinction is "ascent" of magma to the surface of the Earth in the Eastern Siberia, which has caused a huge amount of emissions of CO2 and hydrogen sulfide in the atmosphere. It is possible that the same scenario when it came to disaster that occurred 201.6 million years ago, the scientists conclude.