The 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, by whose name 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.
A real revolution has taken place. Now life has evolved not only in the seas and freshwater bodies, but also on land. Land vertebrates and terrestrial vegetation are widespread. The Devonian period, the flora and fauna of which continued to evolve, was marked by the appearance of the first ammonites (cephalopods). Bryozoans, four-beam corals, and some types of castle brachiopods experienced their heyday.
Life in the 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 intense tectonic movements, cosmic impact and (in general) changes in the environment. Life in the sea has become more diverse compared to silur. The Devonian period of the Paleozoic era is characterized by the predominant development of various species of fish (some scholars even call it the "fish period"). At the same time, the extinction of cystoids, nautiloids, trilobites and graptolites began.
The maximum number reached the number of genera of castle brachiopods. Especially diverse were spiriferids, atripids, rhinchonellids and terebratulides. The richness of species and rapid variability in time was characterized by brachiopods. This group is most important for paleontologists and geologists involved in detailed sedimentation.
The Devonian period, the animals and plants of which were very diverse compared to past eras, was important for the development of corals. Together with stromatoporoids and bryozoans, they began to take part in the construction of reefs. They were assisted by a variety of calcareous algae, which were inhabited by the Devonian Sea.
Invertebrates and vertebrates
Among invertebrates, ostracods, crustaceans, 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 an increasing importance of vertebrates. As mentioned above, it was the "fish age" - shell, bone and cartilaginous fish occupied a dominant position. A new group emerged from this mass. These were fish-shaped jawless organisms. Why were these vertebrates in bloom? 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 were characterized by a sedentary lifestyle. In the middle of the Devonian appeared not only cartilaginous, but also shark. They took a dominant position later - in the Mesozoic.
Vegetation
At the boundary that separated the Devonian from the Silurian, the release of plants to land intensified. They began their rapid resettlement and adaptation to a new terrestrial way of life. The early and middle Devonian took place under the dominance on land of the primitive vascular plants of rhinophytes, which grew in a wetland. By the end of the period, they became extinct everywhere. In the Middle Devonian, spore plants (arthropods, plunders, and ferns) already existed.
The first gymnosperms appeared. Shrubs evolved into tree-like. Mixed ferns spread especially vigorously. Basically, land vegetation developed in coastal regions, where a warm, mild and humid climate has developed. The lands remote from the oceans at that time still existed without any vegetation.
Climate
The Devonian period had a clearer climatic zonality compared with the beginning of the Paleozoic. The East European platform and the Urals were in the equatorial zone (average annual temperature 28 - 31 ° C), Transcaucasia - in the tropical zone (23 - 28 ° C). A similar situation has developed in Western Australia.
Arid climate (dry desert climate) established in Canada. At this time, an active process of salt accumulation was ongoing in the provinces of Saskatchewan and Alberta, as well as in the Mackenzie River basin. Such a characteristic mark in North America left behind the Devonian period. Minerals accumulated in other regions. On the Siberian platform, kimberlite pipes arose , which became the largest diamond deposits.
Humid regions
At the end of the Devonian, an increase in moisture began in Eastern Siberia, which is why 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, southern Australia). It was characterized by high humidity, at which more precipitation fell than could leak into the soil and evaporate.
In these regions (as well as in the northeast and south of Asia), reef masses were located, and rifogenic limestones accumulated. In Belarus, Kazakhstan, and Siberia, variable humidification was established. 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.
Minerals
In the Devonian, in regions with a humid climate, the oldest coal seams on Earth formed. These deposits include deposits in Norway and Timan. The Devonian period includes the oil and gas horizons of the Pechora and Volga-Ural regions. The same can be said of similar deposits in the USA, Canada, Sahara and the Amazon basin.
At this time, reserves of iron ore began to form in the Urals and Tatarstan. In regions with an arid climate, powerful strata of potassium salts were formed (Canada and Belarus). Volcanic manifestations led to the accumulation of pyrite ores in the North Caucasus and on the eastern slopes of the Urals. Lead-zinc and iron-manganese deposits of Central Kazakhstan arose.
Tectonics
By the beginning of the Devonian, mountain structures (Northern Greenland, Northern Tien Shan, Altai) arose and began to rise in the North Atlantic region. Lavrusia at that time was located in equatorial latitudes, Siberia, Korea and China - in temperate latitudes. Gondwana ended up entirely in the southern hemisphere.
Lavrusia was formed at the beginning of the Devonian. The reason for its occurrence was the clash of Eastern Europe and North America. This continent experienced intense uplift (to the greatest extent a watershed ridge). Products of its erosion (in the form of clastic red-colored sediments) have accumulated in Britain, Greenland, Svalbard and Scandinavia. From the north-west and south, Lavrusia 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 slight hilly watersheds. Only in the northwest 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, redflowers spread. Under conditions of increased salinity, deposits of dolomites, gypsum and rock salt accumulated in the central part of the sea basin.