The history of the Earth has four and a half billion years. This huge 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.
Mesozoic period Significant appearance of dinosaurs, the emergence 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 emergence of new species of creatures. First of all, these are dinosaurs, as well as the first mammals.
The 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 an era of global warming. Significant changes have occurred in the tectonics of the Earth. It was at that time that the only existing supercontinent fell into two parts, which subsequently divided into continents that exist 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 disaster that occurred at the end of the Paleozoic on Earth, conditions are observed that contribute little to the prosperity of life. A tectonic fault occurs on the Pangea continent, active volcanoes and mountain peaks form.
The climate becomes warm and dry, in connection with which deserts are formed on the planet, and the level of salt in water bodies rises sharply. However, it was during this unfavorable time that the first dinosaurs, mammals and birds appeared. In many respects this was facilitated by 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 in the Triassic period that those organisms arose that subsequently formed the face of the modern biosphere.
Cynodonts appeared - a group of lizards, which was the ancestor of the first mammals. These lizards were covered with wool and had highly developed jaws, which helped them eat raw meat. The tsinodonts laid their eggs, but the females fed their babies with milk. In the Triassic, the ancestors of dinosaurs, pterosaurs and modern crocodiles, archosaurs, also arose.
Due to the arid climate, many organisms have changed their habitat to aquatic. Thus, new species of ammonites, mollusks, and also bone and ray-fin fish appeared. But the main inhabitants of the deep sea were predatory ichthyosaurs, which, as they evolved, began to reach gigantic proportions.
By the end of the Triassic, natural selection did not allow all animals that appeared to be preserved, many species could not withstand competition with others, stronger and faster. Thus, by the end of the period, land tecodonts, the progenitors of dinosaurs, dominated on land.
Plants in the Triassic
The plant world of the first half of the Triassic did not differ significantly from plants of the end of the Paleozoic era. Different types of algae grew in abundance in water, seed ferns and ancient conifers were widely distributed on land, and in the coastal zones, plum-like plants.
Towards the end of the Triassic, land cover of herbaceous plants covered the land, which greatly contributed to the appearance of various insects. Plants of the mesophytic group also appeared. Some cypress plants have survived to the present. This is a sago palm growing in the zone of the Malay archipelago. Most plant varieties grew on the coastal areas of the planet, and on land conifers predominated.
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. Sedimentary deposits of that era were found in these mountains. The Jurassic period lasted fifty-five million years. Gained geographical significance due to the formation of modern continents (America, Africa, Australia, Antarctica).
The separation of the two continents of Laurasia and Gondwana existing until 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 decreased and began to correspond to a temperate and subtropical climate. Such climatic changes have largely contributed to the development and improvement of the animal and plant world.
Jurassic animals and plants
Jurassic period - the era of dinosaurs. Although other forms of life have also evolved and acquired new forms and species. The seas of that period were filled with many invertebrates, whose body structure is more developed than in the Triassic. Bivalves and intrarack belemnites, the length of which reached three meters, were widespread.
The insect world has also gained evolutionary growth. The appearance of flowering plants provoked the appearance of pollinating insects. New species of cicadas, beetles, dragonflies and other terrestrial insects arose.
Climatic changes that occurred in the Jurassic period led to heavy rainfall. This, in turn, gave impetus to the spread of lush vegetation on the surface of the planet. In the northern zone of the earth, herbaceous fern and ginkgo plants prevailed. The southern belt was made up of tree-like ferns and cicadas. In addition, the Earth was filled with various conifers, cordamite and cypress plants.
Dinosaur era
In the Jurassic Mesozoic, reptiles reached their evolutionary peak, ushering in the era of dinosaurs. In the seas, giant dolphin-like ichthyosaurs and plesiosaurs prevailed everywhere. If ichthyosaurs were inhabitants of an exclusively aquatic environment, then plesiosaurs from time to time needed to land.
Onshore dinosaurs were striking in their diversity. Their sizes ranged from 10 centimeters to thirty meters, and they weighed up to fifty tons. Herbivorous individuals prevailed among them, but ferocious predators also met. A huge number of predatory animals provoked the formation of some protective elements in herbivores: sharp plates, spikes, and others.
The airspace of the Jurassic period was filled with dinosaurs who knew how to fly. Although for the flight they needed to climb high ground. Pterodactyls and other pterosaurs huddled in flocks and planned above the surface of the earth in search of food.
Cretaceous period
When choosing a name for the next period, the main role was played by the written chalk formed in the deposits of dying invertebrate organisms. The period called the Cretaceous became the final in the Mesozoic era. This time lasted eighty million years.
The new continents that have formed move around, and the tectonics of the Earth are increasingly acquiring a form familiar to modern man. The climate became noticeably colder, at this time ice caps of the north and south poles formed. There is also a separation of the planet into climatic zones. But in general, the climate remained quite warm, which was facilitated by the greenhouse effect.
Cretaceous biosphere
Belemnites and mollusks continue to evolve and spread in water bodies, and sea urchins and first crustaceans also develop.
In addition, fish with a hard-bone skeleton are actively developing in water bodies. Insects and worms progressed strongly. On land, the number of vertebrates increased, among which the reptiles reigned dominant. They actively absorbed the vegetation of the earth's surface and destroyed each other. In the Cretaceous period, the first snakes arose that lived both in water and on land. Birds that began to appear at the end of the Jurassic during the Cretaceous were widespread and actively developed.
Among the vegetation, flowering were most developed. Spore plants became extinct due to reproduction, giving way to more progressive ones. At the end of this period, gymnosperms evolved noticeably and began to be replaced by angiosperms.
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 Permian catastrophe marked the beginning of the Mesozoic era, and the second marked its end. Most animal species that actively evolved in the Mesozoic died out. Ammonites, belemnites, bivalve mollusks ceased to exist in the aquatic environment. Dinosaurs and many other reptiles disappeared. Also, many species of birds and insects are gone.
To date, there is no proven hypothesis about what exactly served as the impetus for the mass extinction of fauna in the Cretaceous period. There are versions about the negative impact of the greenhouse effect or about 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, which, when it hit the Earth’s surface, lifted a mass of substances into the atmosphere that covered the planet from sunlight.