The Mesozoic period. Mesozoic era. History of the Earth

The history of the Earth totals four and a half billion years. This vast period of time is divided into four aeons, which in turn are divided into eras and periods. The final fourth eon - Phanerozoic - includes three eras:

• Paleozoic;
• Mesozoic;
• Cenozoic.

The Mesozoic Period It is remarkable for the appearance of dinosaurs, the birth of the modern biosphere and significant geographical changes.

Periods of the Mesozoic Era

The end of the Paleozoic era was marked by the extinction of animals. The development of life in the Mesozoic era is characterized by the appearance of new species of beings. First of all, they are dinosaurs, as well as the first mammals.

Mesozoic lasted one hundred and eighty-six million years and consisted of three periods, such as:

• Triassic;
• Jurassic;
• chalky.

The Mesozoic period is also characterized as the era of global warming. There have also been significant changes in the tectonics of the Earth. It was at that time that the only existing supercontinent split into two parts, which later were divided into continents existing in the modern world.

Triassic

The Triassic period is the first stage of the Mesozoic era. Triassic Lasted for thirty-five million years. After the catastrophe that occurred at the end of the Paleozoic on Earth, conditions are observed that contribute little to the prosperity of life. There is a tectonic breakdown of the Pangea continent, active volcanoes and mountain peaks are formed.

The climate becomes warm and dry, and therefore the desert forms on the planet, and the salt level in the reservoirs rises sharply. However, it is during this unfavorable time that the first dinosaurs, mammals and birds appear. This was largely due to the lack of clearly defined climatic zones and the maintenance of the same temperature throughout the globe.

Fauna of the Triassic

The Triassic period of the Mesozoic is characterized by a significant evolution of the animal world. It was during the Triassic period that those organisms emerged that later shaped the shape of the modern biosphere.

There were cynodonts - a group of lizards, which was the ancestor of the first mammals. These dinosaurs were covered with wool and possessed highly developed jaws, which helped them feed on raw meat. Cynodonts laid eggs, but their young females fed milk. In the Triassic, the ancestors of dinosaurs, pterosaurs and modern crocodiles, arhosaurs, were born.

In connection with the arid climate, many organisms have changed their habitat to water. So there were new species of ammonites, mollusks, as well as bone and ray-fish. But the main inhabitants of the sea depths were predatory ichthyosaurs, which, as they evolved, reached enormous dimensions.

By the end of the Triassic, natural selection did not allow all the animals to survive, many species could not stand competition with others, stronger and faster. Thus, by the end of the period on land tecodons predominated, the progenitors of dinosaurs.

Plants in the Triassic Period

The plant world of the first half of the Triassic did not differ significantly from the plants of the late Paleozoic era. In the water, various types of algae grew abundantly, seed ferns and ancient coniferous plants were widely spread on land, and in the coastal zones - plauniform plants.

By the end of the Triassic, the cover of herbaceous plants covered the land, which largely contributed to the emergence of a variety of insects. Also, plants of the mesophytic group appeared. Some cropland plants have survived to the present day. It is a sago palm growing in the area of the Malay Archipelago. Most species of plants grew on coastal areas of the planet, and on the land dominated by coniferous.

Jurassic period

This period is the most famous in the history of the Mesozoic era. Jura - European mountains that gave the name to this time. In these mountains sedimentary deposits of that epoch were found. The Jurassic period lasted fifty-five million years. Geographical significance has acquired through the formation of modern continents (America, Africa, Australia, Antarctica).

The division of the two continents of Laurasia and Gondwana that existed up to that time served to form new bays and seas and raise the level of the world's oceans. This favorably affected the Earth's climate, making it more humid. The air temperature on the planet dropped and began to match the temperate and subtropical climate. Such climatic changes greatly contributed to the development and improvement of the animal and plant world.

Animals and plants of the Jurassic period

The Jurassic period is the era of dinosaurs. Although other forms of life also evolved and acquired new forms and species. The seas of that period were filled with a multitude of invertebrates, the structure of which is more developed than in the Triassic. Widespread distribution of bivalve mollusks and intracavitary belemnites, the length of which reached three meters.

The world of insects also received evolutionary growth. The appearance of flowering plants provoked the appearance of pollinating insects. There were new species of cicadas, beetles, dragonflies and other terrestrial insects.

The climatic changes that occurred in the Jurassic period resulted in heavy precipitation. This, in turn, gave impetus to the spread of lush vegetation on the surface of the planet. The northern belt of land was dominated by herbaceous paportnikovye and ginkgo plants. The southern belt was made up of treelike ferns and cicadas. In addition, the Earth was filled with various coniferous, cordaite and cadavian plants.

Dawn of the Dinosaurs

In the Jurassic Mesozoic, the reptiles reached their evolutionary peak, marking the beginning of the era of dinosaurs. In the seas, giant dolphin-like ichthyosaurs and plesiosaurs predominated everywhere. If the ichthyosaurs were inhabitants of an exclusively aquatic environment, the plesiosaurs from time to time needed to land on land.

Dinosaurs inhabiting the land, struck by their diversity. Their sizes ranged from 10 centimeters to thirty meters, and they weighed up to fifty tons. Among them, herbivores predominated, but fierce predators also met. A huge number of predatory animals provoked the formation of herbivores some elements of protection: sharp plates, thorns and others.

The air space of the Jurassic period was filled with dinosaurs, able to fly. Although for the flight they had to climb the hill. Pterodactyls and other pterosaurs strayed into flocks and planned over the surface of the earth in search of food.

Cretaceous period

When choosing the name for the next period, the main role played a role, formed in the deposits of wiped out invertebrate organisms, writing chalk. The period called Chalk became the final period in the Mesozoic era. This time lasted eighty million years.

The newly formed continents are moving, and the tectonics of the Earth is becoming more and more familiar to the modern man. The climate became noticeably colder, at that time ice caps of the north and south poles were formed. There is also a division of the planet into climatic zones. But in general, the climate remained warm enough, which contributed to the greenhouse effect.

The Cretaceous Biosphere

Belemnites and mollusks continue to evolve and spread in the reservoirs, sea urchins and the first crustaceans also develop.

In addition, fish with a hardy skeleton actively develop in water bodies. Insects and worms have progressed greatly. On land, the number of vertebrates increased, among which the reptilian reptiles occupied the leading positions. They actively absorbed the vegetation of the earth's surface and destroyed each other. In the Cretaceous period, the first snakes appeared, which lived both in water and on land. Birds that began to appear at the end of the Jurassic period, during the Cretaceous period, became widespread and actively developed.

Among the vegetation the greatest development was the flowering ones. Spore plants because of the characteristics of reproduction died out, giving way to more progressive. At the end of this period the gymnosperms evolved considerably and began to be replaced by angiosperms.

The end of the Mesozoic era

The history of the Earth has two global catastrophes, which served as a mass extinction of the animal world of the planet. The first, the Permian disaster served as the beginning of the Mesozoic era, and the second marked its end. Extinction of most species of animals, actively evolved in the Mesozoic. Ammonites, belemnites, bivalve mollusks ceased to exist in the aquatic environment. Dinosaurs and many other reptiles disappeared. Also there were no many species of birds and insects.

Until now, there is no proven hypothesis about what exactly triggered the mass extinction of fauna in the Cretaceous. There are versions about the negative effect of the greenhouse effect or on the radiation caused by a powerful cosmic explosion. But most scientists are inclined to believe that the cause of extinction was the fall of a giant asteroid that, when struck against the surface of the Earth, lifted into the atmosphere a mass of substances that closed the planet from sunlight.