Geological Devonian period (420 - 358 million years ago) is considered the beginning of the Late Paleozoic. At this time, many biotic events occurred that 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, after whom it 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 died out and disappeared. In their place, new groups of animal plants arose. It was they who determined what the flora and fauna of the Devonian period looked like.
There has been a real revolution. Now life developed not only in the seas and freshwater reservoirs, but also on land. Terrestrial vertebrates and terrestrial vegetation spread widely. The Devonian period, whose flora and fauna continued to evolve, was marked by the appearance of the first ammonites (cephalopods). Bryozoans, four-beam corals, and some species of castle brachiopods experienced their heyday.
Life at sea
The development of the organic world was influenced not only by natural evolution, but alsothe climate of the Devonian period, as well as intense tectonic movements, cosmic impact and (in general) changes in habitat conditions. Life in the sea has become more diverse compared to the Silurian. The Devonian period of the Paleozoic era is characterized by the predominant development of various fish species (some scientists even call it the "fish period"). At the same time, the extinction of cystoids, nautiloids, trilobites and graptolites began.
The number of genera of hinge brachiopods has reached its maximum value. The spiriferids, atripids, rhynchonellids, and terebratulids were especially diverse. Brachiopods were distinguished by the richness of species and rapid variability over time. This group is most important for paleontologists and geologists involved in the detailed dissection of sediments.
The Devonian period, with a great variety of animals and plants compared to past epochs, proved to be important for the development of corals. Together with stromatoporoids and bryozoans, they began to take part in the construction of reefs. They were helped by a variety of calcareous algae that inhabited the Devonian seas.
Invertebrates and vertebrates
Ostracods, crustaceans, tentaculites, blastoids, sea lilies, sea urchins, sponges, gastropods and conodonts developed among invertebrates. 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, it was the "fish age" - armored, bone andcartilaginous fishes took the leading position. A new group emerged from this mass. These were fish-like jawless organisms. Why did these vertebrates flourish? For example, in plate-skinned and armored fish, the front of the body and head were covered with a powerful protective shell - a decisive argument in the struggle for survival. These creatures differed in a sedentary way of life. In the middle of the Devonian, not only cartilaginous, but also sharks appeared. They took the dominant position later - in the Mesozoic.
Vegetation
At the turn that separated the Devonian from the Silurian, the emergence of plants on land became more active. Their rapid resettlement and adaptation to a new terrestrial way of life began. The early and middle Devonian passed under the dominance of primitive vascular plants, rhinophytes, growing in swampy areas on land. By the end of the period they had become extinct everywhere. In the Middle Devonian, spore plants (arthropods, club mosses, and ferns) already existed.
The first gymnosperms appeared. Shrubs have evolved into trees. Heterosporous ferns spread especially vigorously. Basically, terrestrial vegetation developed in coastal regions, where a warm, mild and humid climate developed. The lands remote from the oceans at that time still existed without any vegetation.
Climate
The Devonian period was distinguished by a clearer climatic zonation compared to the beginning of the Paleozoic. The East European platform and the Urals were in the equatorial zone (average annual temperature 28–31 °C), Transcaucasia was in the tropical zone (23–28 °C). A similar situation has developed in Western Australia.
Arid climate (dry desert climate) has been established in Canada. At that time, in the provinces of Saskatchewan and Alberta, as well as in the Mackenzie River basin, there was an active process of s alt accumulation. Such a characteristic trace in North America was left by the Devonian period. Minerals accumulated in other regions as well. Kimberlite pipes appeared on the Siberian platform, which became the largest diamond deposits.
Wet regions
At the end of the Devonian in Eastern Siberia, an increase in moisture began, due to which layers enriched in manganese oxides and iron hydroxides appeared there. At the same time, a humid climate was characteristic of some areas of Gondwana (Uruguay, Argentina, South Australia). It was characterized by high humidity, in which more precipitation fell than could seep into the soil and evaporate.
In these regions (as well as in the northeast and south of Asia) reef massifs were located, reef limestones accumulated. Variable humidification has been established in Belarus, Kazakhstan and Siberia. In the Early Devonian, a large number of semi-isolated and isolated basins formed, within the boundaries of which isolated fauna complexes appeared. By the end of the period, the difference between them began to blur.
Mineral resources
In the Devonian, in regions with a humid climate, the oldest coal seams on Earth were formed. These deposits include deposits in Norway and Timan. The oil and gas bearing horizons of the Pechora and Volga-Ural regions belong to the Devonian period. The same can be said about similar fields in the USA, Canada, the Sahara and the Amazon Basin.
At this time, iron ore reserves began to form in the Urals and Tatarstan. In regions with an arid climate, thick strata of potassium s alts were formed (Canada and Belarus). 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 appeared in Central Kazakhstan.
Tectonics
By the beginning of the Devonian in the North Atlantic region, mountain structures arose and began to rise (Northern Greenland, Northern Tien Shan, Altai). Lavrussia at that time was located in equatorial latitudes, Siberia, Korea and China - in temperate latitudes. Gondwana ended up entirely in the southern hemisphere.
Lavrussia formed at the beginning of the Devonian. The cause of its occurrence was the collision of Eastern Europe and North America. This continent experienced intense uplift (to the greatest extent the watershed range). Its erosion products (in the form of clastic red sediments) accumulated in Britain, Greenland, Svalbard and Scandinavia. From the northwest and south, Lavrussia was surrounded by new folded mountain ranges.structures (Northern Appalachian and Newfoundland fold system).
Most of the territory of the East European Platform was lowland with minor hilly watersheds. Only in the northwest, in the region of the British-Scandinavian mobile belt, were low mountains and large uplands located. In the second half of the Devonian, the lowest parts of the East European Platform were flooded by the sea. On the coastal lowlands, red flowers spread. In conditions of high salinity, deposits of dolomites, gypsum and rock s alt accumulated in the central part of the sea basin.
