When did it start 505 million years ago? Ordovician period, animal world existed only in the sea, but by the end of this period the animals had already taken their first steps on land.
During Ordovician period Almost all of the world's landmass was south of the equator. The South Pole was located in Africa, which was connected to South America, Antarctica and Australia. This entire territory made up the ancient giant continent - Gondwana. Animals of this period bred abundantly in the shallow seas, but climatic changes put an end to these fertile times. Ancient traces left by glaciers indicate that a layer of ice formed over the giant continent by the end of the Ordovician period and the climate became so cold that more than half of all animal species extinct.

Filling the sushi.

Like all major chapters in Earth's history, the Ordovician period began with a new wave of speciation after a small extinction event. Compared to the mass extinction that ended the Ordovician period, this wave was small in scale, but it had a particularly strong impact on trilobites, which became the most abundant arthropods at the time. Thus, the Ordovician period began with a large number of biological niches, which soon began to be filled.
One of the groups of animals that filled this gap were cephalopods nautiloids, related to the current nautilus boats. Unlike earlier molluscs that lived on the seabed, nautiloids were able to swim. They could hover motionless over the sea floor, watching for prey with their developed eyes, or rush rapidly, driven by the reactive force of a stream of water released from the mantle cavity.
This new image life became possible thanks to the unusual structure of the shell of these animals. They were conical or spiral-shaped, but they did not consist of a simple chamber inside, like snail shells, but were divided into a whole series of chambers, separated from each other by thin partitions. The animal's body was in the largest chamber, while the remaining chambers were filled with gas. The nautiloid could control the amount of gas in the chambers, reducing or increasing it, like a submarine.
This new form and the structure of the shell was a sign of the times - more and more species of animals began to move from the seabed into the water column, even though it was risky.
On a note: Nautiloids were the largest animals in the seas of the Ordovician period. With straight or spiral shells, as shown in the picture accompanying this article, they hunted for prey on a seabed covered with a carpet of algae, corals and crinoids - distant relatives of the starfish - which had thin stalks and tentacles for collecting food . Planktonic animals drifting in the water were numerous, but most animals, however, found food close to the seabed.

Vacuum cleaner fish.

Although the remains of fish-like animals are among the finds dating back to the Cambrian period, it is the Ordovician that represents the period when such animals spread quite widely. Compared to nautiloids, these early vertebrates were small animals, and their downward-facing mouth openings suggest that they fed on what they found on the seafloor. They did not have jaws, although they could probably move their "lips". Most of them looked like a living vacuum cleaner, sucking up food particles that had settled to the bottom.
These fish-like creatures - known as heterostracans— they owed their survival to a shield that consisted of bone plates and covered the front of their body. This reliable covering became a common feature of early vertebrates and marked the beginning of the underwater struggle for life.

Refuge on land.

When the seas became too populated and too dangerous, some animals began to seek refuge in fresh waters and marshy shallows along the sea coasts. Here food could be found in the form of lower plants - algae. But in the air, living cells quickly dried out, so it was risky for soft-bodied animals to go onto land. In arthropods, the entire body was protected by a shell, which helped stop the drying out process. No remains of these particular pioneer animals have been found, but their tracks in the fossilized mud indicate that they were likely the first living creatures to reach land 450 million years ago.

The history of the blue planet spans several eras of life. The Paleozoic era is considered one of the most ancient. This geological era precedes the Mesozoic and follows the Neoproterozoic. The era began approximately 540 million years ago and lasted for 289 of them. The Paleozoic is divided into several periods. One of these six periods is Ordovician.

Ordovician period considered second after the Cambrian within the Paleozoic era. This time began approximately 485 million years ago, lasting about 42 of them.

In scientific understanding Ordovician system is a complex of sediments of the Paleozoic group, named after the ancient Ordovician tribe. Representatives of the tribe lived within modern Wales, which is located on the islands of Great Britain. Today the Ordovician is recognized as an independent system. Geologists note that the period was experienced by the planet in most of its parts - continental and island.

Geological features of the Ordovician period

At the start of the Ordovician period, the northern and southern parts of America were located close to the European and African continents. Australia was integral part Asia and was also close to Africa. The Earth's poles were located in North Africa and in northern zone Pacific Ocean respectively. Beginning of the Ordovician marked by the dominance of the Gondwana continent in the south of the planet. The continent included South America, part Atlantic Ocean, Australia, Africa, northern Asia, Indian Ocean. Europe and North America were in the process of slowly moving away from each other, and sea levels were rising rapidly. The bulk of the land was found in warm latitudes. In Gondwana, hills, mountain and continental glaciers appeared one after another.

In southern France and Spain, during the Ordovician period, there was icing of the earth's surface. Archaeologists also discovered traces of ice in Brazil and the western part of the Sahara. Mid-Ordovician one could observe the expansion of the space of the seas. In the west of the northern and southern parts of America, Britain, the southeastern part of Australia, the Ural-Mongolian belt, traces of Ordovician sediments were found, about 10,000 meters. A large number of volcanic formations were located in these zones, as evidenced by the accumulation of lavas. There are also siliceous rocks - phthanides, jasper. On modern Russian territory Traces of the Ordovician period are clearly visible within the Urals, Novaya Zemlya, the New Siberian Islands, Taimyr, Kazakhstan, individual Central Asian territories, the Siberian and European platforms.

Ordovician climate

Ordovician climate can be divided into several types:

• moderate;
• nival;
• tropical;
• subtropical.

Towards the end of the Ordovician period, a global cooling occurred, during which in tropical zones the overall temperature dropped by five degrees, and in the subtropics by 16 on average. Anomalous cooling occurred in high latitudes. The climate of the Middle Ordovician was not characterized by anomalous climatic conditions; in general, the climate was warmer when compared with the previous era. Proof of this observation is the wide distribution of limestone rocks.

Minerals of the Ordovician period

Of the mineral resources formed during the Ordovician era, the first to be highlighted are gas and oil. The leader in the number of deposits of these resources is the territory of North America. The main group of phosphorite and oil shale deposits is concentrated here. The deposits were formed as a result of active geological processes involving magma.

Seas during the Ordovician period

The Ordovician period is notable for the large-scale expansion of the sea. During the Middle Ordovician era, the level of the seabed began to decrease, provoking the active accumulation of sedimentary rocks. These are volcanic ash, sand, and clastic rocks, which together form black silt. Shallow seas were located within the borders of Europe and North America.

Plants and animals of the Ordovician period

During the Ordovician period, the representatives of the flora did not actually change when compared with the previous era. Basically, science refers to numerous types of algae. The first species appear on earth plants of the Ordovician period- most of them are mosses. The inner world of water is more diverse and plays a large role in the formation of the modern planet. In the Ordovician, the first fish appeared here, albeit small in size - no more than a matchbox in length. Marine inhabitants acquire hard surfaces, adapting to changes in the seabed. Living organisms had to rise higher above the bottom due to large quantity sediments. The number of animals feeding in seawater is growing. Evolution acts unevenly - some representatives of the vertebrate class have already overcome the path of development, others are only at the initial stage. The end of the Ordovician period was marked by the wide distribution of vertebrate organisms and the development of the echinoderm class, many of which exist to this day. For example this sea ​​stars.

Active life activity begins in gastropods and elasmobranchs - the number of their representatives and subspecies increases sharply, and a primitive form of nautiloids develops - four-branched cephalopods. This type of organism still exists today in the depths of the Indian Ocean. They live in shells, but they are bent, while animals of the Ordovician period, who were their ancestors, lived in straight-shaped shells. These mollusks led the lifestyle of predators.

From the latest type animals should be noted graptolites. Graptolites created colonies and reproduced by budding. The now extinct species could not be classified by science for a long time - at different times it was classified as coelenterates and invertebrates. Among the modern relatives of graptolites, there are some microorganisms that live in the North Sea and participate in the activity of corals.

On the territory of modern Colorado, the remains of a jawless fish were discovered, some of its fragments resembled a shark. The findings indicate clear differences between the jawless inhabitants of the seas of the Ordovician period and modern species. For the first time, conodonts similar to modern eels appeared during this period. These are the first animals to have teeth.

Today, science has discovered about six hundred species that lived in the sea during the Ordovician period. The vast majority of species have died due to climate change. The main destructive factor is global cooling. The drying up of shallow seas led to the death of all their inhabitants. For the same reasons, representatives of the plant world also died.

Why did living organisms become extinct?

There is no exact answer to why living creatures became extinct during the Ordovician period. One can be content with only numerous versions of the explanation of what happened. Today scientists adhere to the following versions:

1. There was a burst of gamma rays within the boundaries of the solar system.
2. There was a massive fall of cosmic bodies to the earth, which destroyed all life.
3. The death of animals was facilitated by the process of mountain formation. Proud rocks weather and become part of the soil. As a result, the amount of carbon decreases and cooling occurs.
4. The cooling occurred as a result of the continental movement towards the South Pole, and then glaciation and a decrease in the water level in the ocean occurred.
5. The world's oceans were oversaturated with metals, resulting in water poisoning.

Today, the real reason for the death of living organisms during the Ordovician period has not yet been discovered by science.

The Ordovician period, or Ordovician (485 - 444 million years ago) is one of the least known geological periods in the history of the Earth. It did not witness the same burst of evolutionary activity that characterized the previous one; rather, it was a time when the earliest arthropods and vertebrates expanded their presence in the world's oceans. The Ordovician is the second period (542-252 million years ago), which was preceded by the Cambrian, and then it was replaced by and periods.

Climate and geography

During most of the Ordovician period, global climate conditions were as warm as during the previous Cambrian; the average air temperature in the world was about 50 ° C, and the water temperature in the seas reached 45 ° C. However, by the end of the Ordovician, the climate was much colder, as an ice cap formed at the south pole and glaciers covered the adjacent land areas. Plate tectonics transported the Earth's continents to some strange places; For example, most of landmass that later became Australia and Antarctica were in the northern hemisphere! These early continents were biologically significant: their coastlines provided protected habitats for shallow-water marine organisms.

Sea life

Invertebrates

During this period, the Great Ordovician Radiation occurred, an event of significant biodiversity (biodiversification) that was second only to the Cambrian Explosion in importance for the early history of life on Earth.

Over the course of about 25 million years, the number of marine organisms around the world increased significantly, with new species, trilobites, brachiopods, and (early starfish) appearing. One theory is that the formation and migration of new continents helped maintain biodiversity along their shallow coastlines, although climatic conditions likely also played a role.

On the other side of the evolutionary coin, the end of the Ordovician period marked the first great thing in the history of life on Earth (or, let's say, the first for which scientists have sufficient fossil evidence). Changing global temperatures, accompanied by a sharp drop in sea level, have destroyed great amount species, although in general it recovered quite quickly by the beginning of the next Silurian period.

Vertebrates

Almost everything there is to know about life during the Ordovician period lies in Arandaspis and Astraspis. These were two genera of the first jawless, lightly armored prehistoric fish, measuring 12 to 14 cm in length and vaguely resembling giant tadpoles. The bone plates of Arandaspis and its ilk later developed into true skeletons. Some paleontologists also believe that the numerous, tiny, worm-like conodonts found in Ordovician deposits are true vertebrates; if so, they may have been the first vertebrates on Earth to have teeth.

Vegetable world

As in the previous Cambrian, evidence of terrestrial plant life in the Ordovician is elusive. If land plants existed, they consisted of microscopic green algae floating on or below the surface of the water. However, it was not until after the Silurian period that the first land plants of which there is hard fossil evidence appeared.

ORDOVICIAN Period
505-430 million l. n.

The Paleozoic era left its mark on the history of the development of the Earth: violent geophysical processes, the formation of the main continents and seas, the emergence of marine and land animals... The Ordovician period - the second from the bottom of six periods in the historical geological system of division - follows the Cambrian and precedes the Silurian.

History of the study

The history of the geological and biological development of the Earth can be traced through the study of radiological studies of the strata that were formed in each period. The Paleozoic era is no exception. The Ordovician period was identified and described by English researchers Murchison and Lapworth, who proposed its name. The Ordovicians were the name given to an ancient tribe that lived in what is now Wales. It is in this place, in the area of ​​Areninga and Bala, that geological strata corresponding to the period that occurred 500 million years ago were identified for 60 million years.

At the XXI session of the International Geological Congress, the Ordovician period acquired the status of an independent system.

Ordovician divisions

The Ordovician system is divided into three periods: lower, middle and upper. According to the generally accepted international classification, they correspond to certain tiers:

• Lower Ordovician: Tremadocian, Floian.
• Middle Ordovician: Dalingian, Darriwilian.
• Upper Ordovician: Sandbian, Katian, Hirnantian.

The geological history of the Ordovician period is studied in many countries; paleontologists put forward their own systems for dividing periods, somewhat different from the international version.

Continents and oceans

At the border of the Cambrian and Ordovician periods, the distribution of ocean and land looked like this: North America and Greenland formed a single continent, Laurentia. To the south of it was the Brazilian mainland. The African continent included Madagascar and Arabia. North - Russian continental platform, to the east of it Angarida, the Chinese and Australian continents. Tectonic movements during the Ordovician period led to the convergence of the Russian, Siberian, Chinese and North American platforms and the formation of a single large continent of Laurasia in the north. The southern platforms - Hindustan, African, Antarctic, South American, Australian - united into the huge continent of Gondwana. The two large continents were separated by the Tesis Sea - a place where in modern times the mountain systems of Europe, North Africa, Asia, and South America are located. High seismic activity is characteristic of these regions to this day.

Climate

Volcanoes continued to rage throughout the Ordovician period. The climate became warmer and wetter. The current hottest part of the world - Africa - in those days was located under the very pole, as evidenced by traces of glaciations on its territory. The increase in sea area led to a decrease in the northern deserts and the complete disappearance of the southern dry zone. Active seismic conditions lead to the accumulation of thick volcanic rocks. Tuffs and lava fill the sea trenches. Black volcanic ash and sand accumulate on the seabed, which gradually sinks.

Minerals

Climatic conditions, tectonic and seismic activity of this period led to the formation of special accumulations in the earth's crust, characteristic only of the Ordovician. The Ordovician period is distinguished by deposits of rocks of marine origin: limestone, shale, sandstone. Volcanic lava and magmatic processes lead to the formation of phosphorites, oil shale, oil, iron and other ores, granite, marble, and shell rock.

Ordovician period: flora

In the Ordovician, as in the previous Cambrian period, the class of plants is represented mainly by red and green algae. Plants that appeared on land are observed in very small numbers in the studied sections; apparently, these were the first examples of small tubular representatives of the flora, which were just beginning their continental development. For a more extensive conquest of the soil, optimal conditions were formed only later Devonian period, when the outbursts of volcanic passions subsided somewhat and suitable humidity established. The first seaweeds are unicellular lower forms of plants, which, however, have survived to this day. Algae coexisted with plant forms such as fungi and bacteria.

Animals of the Ordovician period

As you know, the origin of the animal world began in the ocean depths. In this regard, the Ordovician is characterized by explosive progress in the development of many new species and forms of major marine organisms.

Trilobites, peculiar marine arthropods that appeared in Cambrian times, experienced unprecedented progress. During the Ordovician period, the number of their genera increased to 77; they differed in size and lifestyle. Some species of trilobites were blind, but most of them had eyes with facets ranging from 10 to 1200. The body of these arthropods consisted of several segments (from 2 to 29) and was covered with spines, which protected them from enemies and kept the trilobite on the surface of the water.

During the period we are considering (Ordovician), cephalopods received a surge in development. The ancestors of modern cuttlefish, squid and octopuses formed in those distant times many species and subspecies, ranging in size from a few centimeters to several meters.

In the sandy layers of the Ordovician period, remains of foraminiferal, radiolarian, and graptolite nuclei were found.

Bryozoans, echinoderms, tabulates, and corals have made significant progress in development. The Ordovician is associated with the appearance of the most ancient vertebrates - jawless fish agnates. In their structure, the first cartilaginous fish resembled modern hagfish. It was flexible, like a loach, a creature with a cartilaginous spine along its slippery body. The first vertebrates still had a cover in the form hard shell, which protected from external damage, but were already more mobile than their predecessors, since the spine served as a support for developing muscles. At the very end of the period, the gills of some species turned into jaws, and the horny plates into teeth. The first ferocious predators - placoderms - looked terrifying, reached three meters in length, and moved quickly.

Ordovician catastrophe

Many people know the historical fact about the mass extinction of dinosaurs on the planet, but few know that the first significant catastrophe occurred about 200 years before the appearance of dinosaurs. In the late Ordovician period, the animal world lost approximately 60% of the species that existed at that time. Most living organisms belonged to primitive forms and existed primarily in an aquatic environment, however, in terms of the number of dead individuals, this event is second in the list of similar mass extinctions and third in percentage species and genera that have disappeared forever from the face of the Earth.

Versions of the causes of the Ordovician catastrophe

As with dinosaurs, the extinction of Ordovician protists is hotly debated among paleontologists. Experts are discussing the reasons that caused the tragedy. There are five main versions:

• First cosmic: a powerful burst of gamma waves near the Solar System.
• The second is cosmic: the fall of large meteorites or the collision of large asteroids.
• One of the reasons could be the intensive formation of mountain systems, in particular the Appalachians, which leads to intense weathering and changes in the composition of soil and water.
• Climate version. The shift of Gondwana towards the South Pole led to a sharp cooling. Concentration decreased carbon dioxide, there was a drop in the level of the World Ocean, followed by glaciation.
• Opponents of the above version are researchers of the chemical composition of fossil microorganisms. They are sure that the reason lies in a sharp change in the ratio of carbon dioxide and oxygen in the air, and the saturation of water with the elements iron, lead, copper, and manganese. Living organisms underwent metamorphosis, and subsequently entire species and genera became completely extinct.

Major events of the Ordovician period

To summarize, we can highlight several main and most important events of that era, which significantly influenced the course of the further history of the development of life on Earth.

• The area of ​​the seas has increased (compared to the previous period).
• The formation of the main platforms has been completed.
• There was an accumulation of thick layers of tuff, lava, sedimentary rocks, and clastic deposits.
• Deposits of iron and manganese ores, gold, oil, and building materials are being established.
• The emergence of folded regions and mountain systems determined certain boundaries of regions, which explains the difference in the development of vegetation in different parts globe.
• Plants of the Ordovician period are represented by rapidly developing algae, the first of which appear on land, albeit in small quantities. Presumably, they became the harbingers of the first land tubular plants - rhiniophytes.
• Rapid development of marine inhabitants: trilobites, echinoderms, mollusks, branchapods, bryozoans, corals.
• The most important and important event of the Ordovician was the appearance of the first vertebrates - cartilaginous jawless fish.