Devonian period of the Paleozoic era

The geological Devonian period (420 - 358 million years ago) is considered the beginning of the late Paleozoic. At that time, many biotic events took place, which greatly influenced the further development of life on Earth. The Devonian system was established in 1839 by scientists Adam Sedgwick and Roderick Murchison in the English county of Devonshire, by whose name she was named.

Flora and fauna

On the eve of the Devonian, there was a mass extinction of the organic world. Many species, formerly widespread on Earth, simply faded and disappeared. In their place, new groups of plant animals have emerged. It was they who determined what the flora and fauna of the Devonian period looked like.

There was a real revolution. Now life developed not only in the seas and freshwater reservoirs, but also on land. Land vertebrates and terrestrial vegetation were widely spread. The Devonian period, whose flora and fauna continued to evolve, was marked by the appearance of the first ammonites (cephalopods). Its flourishing experienced bryozoans, four-coral, some types of castle brachiopods.

Life at sea

The development of the organic world was influenced not only by natural evolution, but also by the climate of the Devonian period, as well as intensive tectonic movements, cosmic impact and (in general) changes in the environment. Life in the sea became more diverse than the Silurian. The Devonian period of the Paleozoic era is characterized by the predominant development of a variety of fish species (some scientists even call it the "fish period"). At the same time, the extinction of cystoids, nautiloids, trilobites and graptolites began to fade.

The maximum number reached the number of genera of brachiopods. Spiriferides, atripids, rhinchonellids and terrethralids were especially diverse. The richness of species and the rapid variability over time were distinguished by brachiopods. This group is most important for paleontologists and geologists dealing with detailed dismemberment of sediments.

The Devonian period, whose animals and plants were distinguished by a great variety in comparison with previous eras, proved to be important for the development of corals. Together with the stromatopoids and bryozoans, they began to take part in the construction of reefs. They were helped by a variety of calcareous algae, which were inhabited by the Devonian seas.

Invertebrates and vertebrates

Among invertebrates, ostracods, rakoskorpions, tentaculites, blastoids, sea lilies, sea urchins, sponges, gastropods and conodonts developed. According to the remains of the latter, experts today determine the age of sedimentary rocks.

The Devonian period was marked by the increasing importance of vertebrates. As mentioned above, this was the "fish age" - the armored, bone and cartilaginous fish took the leading position. A new group has emerged from this mass. These were fish-like carnivorous organisms. Why did these vertebrates flourish? For example, in plateloaders and shellfish, the front of the trunk and head were covered with a powerful protective shell - the decisive argument in the struggle for survival. These creatures were characterized by a sedentary lifestyle. In the middle of the Devonian appeared not only cartilaginous, but also sharks. They occupied the dominant position later - in the Mesozoic.

Vegetation

At the turn separating the Devonian period from the Silurian, the output of plants on land intensified. They began their rapid resettlement and adaptation to a new land way of life. Early and Middle Devonian passed under the dominance of primitive vascular plant rhinophytes growing on wetlands. By the end of the period they were extinct everywhere. On the average Devonian spore plants already existed (arthropods, placenta and ferns).

The first gymnosperms appeared. Shrubs evolved into treelike. Especially vigorously spread raznosporovye ferns. In general, terrestrial vegetation developed in coastal regions, where a warm, mild and humid climate developed. Removed from the oceans of the earth at that time still existed without any vegetation.

Climate

The Devonian period was distinguished by a clearer climatic zonality in comparison with the beginning of the Paleozoic. The East-European Platform and the Urals were in the equatorial belt (average annual temperature 28-31 ° C), in the Transcaucasus - in the tropical belt (23-28 ° C). A similar situation has developed in Western Australia.

The arid climate (dry desert climate) was established in Canada. At this time in the provinces of Saskatchewan and Alberta, as well as in the Mackenzie Basin was an active process of salt accumulation. This characteristic trail in North America was left by the Devonian period. Minerals accumulated in other regions. Kimberlite pipes appeared on the Siberian platform , which became the largest deposits of diamonds.

Wet regions

At the end of the Devonian in East Siberia, the growth of moistening began, because of which layers appeared enriched with manganese oxides and iron hydroxides. At the same time, humid climate was characteristic for some areas of Gondwana (Uruguay, Argentina, southern Australia). It was characterized by high humidity, at which the amount of precipitation was greater than it could leak into the soil and evaporate.

In the listed regions (and also in the northeast and south of Asia) there were reef massifs, reefogenic limestones were accumulating. In Belarus, Kazakhstan and Siberia, variable moisture was established. In the early Devonian a large number of semi-isolated and isolated basins were formed, within the boundaries of which isolated complexes of fauna appeared. By the end of the period the difference between them began to blur.

Minerals

In the Devonian in regions with a humid climate, the most ancient coal seams on the Earth were formed. These deposits include deposits in Norway, and on Timan. The Devonian period includes the oil and gas bearing horizons of the Pechora and Volga-Ural regions. The same can be said about similar deposits of the USA, Canada, the Sahara and the Amazon basin.

At this time in the Urals and in Tatarstan, iron ore reserves began to form. In the regions with arid climate powerful potassium salts formed (Canada and Byelorussia). Volcanic manifestations led to the accumulation of copper-pyrite ores in the North Caucasus and on the eastern slopes of the Urals. Lead-zinc and iron-manganese deposits of Central Kazakhstan appeared.

Tectonics

By the beginning of the Devonian in the North-Atlantic region, mountain structures have arisen and begun to ridge (Northern Greenland, Northern Tien Shan, Altai). Lavrusia at this time was located in the equatorial latitudes, Siberia, Korea and China - in temperate latitudes. Gondwana was entirely in the southern hemisphere.

Lavrusia was formed at the beginning of the Devonian. The cause of its emergence was the clash of Eastern Europe and North America. This continent experienced an intense uplift (most of the watershed ridge). The products of its erosion (in the form of detrital red-colored sediments) accumulated in Britain, Greenland, Spitsbergen and Scandinavia. From the north-west and south, Lavrussia was surrounded by new folded mountain structures (the folded system of the Northern Appalachians and Newfoundland).

Most of the territory of the East European Platform was a lowland with insignificant hilly watersheds. Only in the north-west in the area of the British-Scandinavian mobile belt were low mountains and large elevations. In the second half of the Devonian period, the lowest parts of the East European platform were flooded by the sea. On the coastal lowlands spread red flowers. In conditions of increased salinity, deposits of dolomite, gypsum and rock salt accumulated in the central part of the sea basin.