Geological stages of the development of the earth. Dividing the history of the earth into eras and periods

The bones of dinosaurs and amazing extinct animals have been found in different eras of human history. In the absence of science, legends about giants or dragons were composed from the bones found. Based on paleontological findings, only modern people with the development of science.

Earth formation

Our planet was formed about 4.5 billion years ago from stellar dust and solid particles. With an increase in gravity, the Earth began to attract debris and stones from space, which fell to the surface, gradually warming up the planet. Over time, the top layer thickened and began to cool. The hot mantle maintains heat so far, preventing the Earth from turning into a block of ice.

For a long time the planet was in a lifeless state. The atmosphere was filled with various gases and contained no oxygen. Due to the release of a large amount of steam from the bowels of the Earth and gravity, dense clouds began to form. Intense rains contributed to the emergence of the World Ocean, in which life originated.

Rice. 1. Formation of the Earth.

Oxygen appeared in the atmosphere with the advent of the first photosynthetic plants.

Stages of development

Life on Earth is connected with geological eons and eras. An eon is a large segment of geological history that combines several eras. In turn, eras are subdivided into periods. Each era is characterized by the individual development of the animal and plant world, which often depended on the climate, the state earth's crust, underground activities.

Rice. 2. Eras of the geological history of the Earth.

More detailed description eons is presented in the table of the main stages in the development of life on Earth.

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is the totality of all forms of the earth's surface. They can be horizontal, inclined, convex, concave, complex.

The height difference between the high peak on land, Mount Chomolungma in the Himalayas (8848 m), and the Mariana Trench in the Pacific Ocean (11,022 m) is 19,870 m.

How was the relief of our planet formed? In the history of the Earth, two main stages of its formation are distinguished:

• planetary(5.5-5.0 million years ago), which ended with the formation of the planet, the formation of the core and mantle of the Earth;
• geological, which began 4.5 million years ago and continues to this day. It was at this stage that the formation of the earth's crust occurred.

The source of information about the development of the Earth during the geological stage is primarily sedimentary rocks, which in the vast majority were formed in the aquatic environment and therefore occur in layers. The deeper the layer lies from the earth's surface, the earlier it was formed and, therefore, is more ancient with respect to any layer that is closer to the surface and is younger. This simple reasoning is based on the concept relative age of rocks, which formed the basis for the construction geochronological table(Table 1).

The longest time intervals in geochronology are − zones(from Greek. aion- century, epoch). There are such zones as: cryptozoic(from Greek. cryptos- hidden and zoe- life), covering the entire Precambrian, in the deposits of which there are no remains of skeletal fauna; phanerozoic(from Greek. phaneros- explicit, zoe- life) - from the beginning of the Cambrian to our time, with a rich organic life, including skeletal fauna. The zones are not equal in duration, so if the Cryptozoic lasted 3-5 billion years, then the Phanerozoic lasted 0.57 billion years.

Table 1. Geological table

The zones are divided into era. In the cryptozoic, there are Archean(from Greek. archaios- primordial, ancient aion- century, era) and Proterozoic(from Greek. proteros- earlier, zoe - life) era; in the Phanerozoic Paleozoic(from Greek ancient and life), Mesozoic(from Greek. tesos - middle, zoe - life) and Cenozoic(from Greek. kainos- new, zoe - life).

Eras are divided into shorter periods of time - periods established only for the Phanerozoic (see Table 1).

The main stages in the development of the geographical envelope

The geographical envelope has come a long and difficult path of development. There are three qualitatively different stages in its development: pre-biogenic, biogenic, and anthropogenic.

pre-biogenic stage(4 billion - 570 million years) - the longest period. At this time, the process of increasing the thickness and complicating the composition of the earth's crust took place. By the end of the Archean (2.6 billion years ago), a continental crust about 30 km thick had already formed over vast areas, and in the Early Proterozoic, protoplatforms and protogeosynclines separated. During this period, the hydrosphere already existed, but the volume of water in it was less than now. Of the oceans (and then only by the end of the early Proterozoic) one took shape. The water in it was salty and the salinity level most likely was about the same as now. But, apparently, in the waters of the ancient ocean, the predominance of sodium over potassium was even greater than now, there were also more magnesium ions, which is associated with the composition of the primary earth's crust, the weathering products of which were carried into the ocean.

The Earth's atmosphere at this stage of development contained very little oxygen, and there was no ozone screen.

Life most likely existed from the very beginning of this stage. According to indirect data, microorganisms lived already 3.8-3.9 billion years ago. The discovered remains of the simplest organisms are 3.5-3.6 billion years old. However, organic life from the moment of its inception to the very end of the Proterozoic did not play a leading, determining role in the development of the geographical envelope. In addition, many scientists deny the presence of organic life on land at this stage.

The evolution of organic life to the pre-biogenic stage proceeded slowly, but nevertheless, 650-570 million years ago, life in the oceans was quite rich.

Biogenic stage(570 million - 40 thousand years) lasted during the Paleozoic, Mesozoic and almost the entire Cenozoic, with the exception of the last 40 thousand years.

The evolution of living organisms during the biogenic stage was not smooth: eras of relatively calm evolution were replaced by periods of rapid and deep transformations, during which some forms of flora and fauna died out and others became widespread.

Simultaneously with the appearance of terrestrial living organisms, soils began to form in our modern understanding.

Anthropogenic stage began 40 thousand years ago and continues today. Although man as a biological species appeared 2-3 million years ago, his impact on nature long time remained extremely limited. With the advent of Homo sapiens, this impact has increased significantly. It happened 38-40 thousand years ago. From here the anthropogenic stage in the development of the geographic envelope takes its countdown.

Archean era. The beginning of this ancient era is considered not the moment of the formation of the Earth, but the time after the formation of the solid earth's crust, when mountains and rocks already existed and the processes of erosion and sedimentation came into play. The duration of this era is approximately 2 billion years, i.e., it corresponds to all other eras taken together. The Archean era seems to have been characterized by catastrophic and widespread volcanic activity, as well as deep uplifts culminating in the formation of mountains. The high temperature, pressure and mass movements that accompanied these movements apparently destroyed most of the fossils, but some data about the life of those times still survived. In the Archeozoic rocks, graphite or pure carbon is found everywhere in scattered form, which probably represent altered remains of animals and plants. If we accept that the amount of graphite in these rocks reflects the amount of living matter (and this, apparently, is true), then in the Archaean this living matter probably existed very much, since there is more carbon in the rocks of this age than in coal seams of the Appalachian Basin.

Proterozoic era. The second era, lasting about 1 billion years, was characterized by the deposition of a large amount of precipitation and at least one significant glaciation, during which ice sheets extended to latitudes less than 20 ° from the equator. A very small number of fossils were found in the Proterozoic rocks, which, however, testify not only to the existence of life in this era, but also to the fact that evolutionary development advanced far ahead by the end of the Proterozoic. Spicules of sponges, remains of jellyfish, fungi, algae, brachiopods, arthropods, etc. have been found in Proterozoic deposits.

Palaeozoic. Between the deposits of the Upper Proterozoic and the initial layers of the third, Paleozoic era, there is a significant break caused by mountain building movements. For 370 million years of the Paleozoic era, representatives of all types and classes of animals appeared, with the exception of birds and mammals. Since different species of animals existed only for certain periods of time, their fossils allow geologists to compare deposits of the same age found in different places.

• Cambrian period [show] .

  Cambrian period- the most ancient department Paleozoic era; It is represented by rocks abounding in fossils, so that the appearance of the Earth at this time can be reconstructed with sufficient accuracy. The forms that lived during this period were so diverse and complex that they must have descended from ancestors that existed at least in the Proterozoic, and possibly in the Archaean.

  All modern types animals, with the exception of chordates, already existed and all plants and animals lived in the sea (the continents, apparently, were lifeless deserts until the late Ordovician or Silurian, when the plants moved to land). There were primitive, shrimp-like crustaceans and forms resembling arachnids; some of their descendants have survived, almost unchanged, to the present day (horse crabs). The seabed was covered with solitary sponges, corals, stalked echinoderms, gastropods and bivalves, primitive cephalopods, brachiopods and trilobites.

  Brachiopods - sessile animals with a bivalve shell and feeding on plankton, flourished in the Cambrian and in all other systems of the Paleozoic.

  Trilobites are primitive arthropods with an elongated flat body, covered on the dorsal side with a hard shell. Two grooves stretch along the shell, dividing the body into three parts, or lobes. Each body segment, with the exception of the very last, bears a pair of biramous limbs; one of them served for walking or swimming and it had a gill. Most trilobites were 5-7.5 cm long, but some reached 60 cm.

  In the Cambrian, both unicellular and multicellular algae existed. One of the best preserved collections of Cambrian fossils was collected in the mountains of British Columbia. It includes worms, crustaceans, and a transitional form between worms and arthropods, similar to the living peripatus.

  After the Cambrian, evolution was mainly characterized not by the emergence of completely new types of structure, but by the branching of already existing lines of development and the replacement of the original primitive forms by more highly organized ones. It is probable that pre-existing forms have reached such a degree of adaptability to the environment that they have acquired a significant preponderance over any new, unadapted types.

• Ordovician period [show] .

  During the Cambrian period, the continents began to gradually sink into the water, and in the Ordovician period this sinking reached its maximum, so that a significant part of the current land was covered with shallow seas. Huge cephalopods lived in these seas - animals similar to squid and nautilus - with a straight shell from 4.5 to 6 m long and 30 cm in diameter.

  The Ordovician seas must have been very warm, as warm-water corals spread as far as Lake Ontario and Greenland at this time.

  The first remains of vertebrates were found in the Ordovician deposits. These small animals, called corymbs, were bottom forms, devoid of jaws and paired fins (Fig. 1.). Their carapace consisted of heavy bony plates on the head and thick scales on the body and tail. Otherwise, they were similar to modern lampreys. They apparently lived in fresh water, and their shell served to protect against giant predatory water scorpions called eurypterids, which also lived in fresh water.

• Silurian [show] .

  The Silurian period saw two major events biological significance: land plants developed and air-breathing animals appeared.

  The first land plants seem to have been more like ferns than mosses; ferns were the dominant plants also in the subsequent Devonian and lower Carboniferous.

  The first air-breathing land animals were arachnids, somewhat reminiscent of modern scorpions.

  The continents that had been low during the Cambrian and Ordovician times rose, especially in Scotland and northeastern North America, and the climate became much cooler.

• Devonian [show] .

  

  

  

  During the Devonian, the first armored fishes gave rise to many different fishes, so that this period is often called the "time of the fishes."

  Jaws and paired fins first developed in armored sharks (Placodermi), which were small, shelled freshwater forms. These animals were characterized by a variable number of paired fins. Some had two pairs of fins, corresponding to the fore and hind limbs of higher animals, while others had up to five pairs of additional fins between these two pairs.

  During the Devonian, real sharks appeared in fresh waters, which showed a tendency to migrate to the ocean and to lose their bulky bone carapace.

  The ancestors of bony fishes also originated in Devonian freshwater streams; by the middle of this period, they had a division into three main types: lungfish, lobe-finned and ray-finned. All these fish had lungs and a shell of bony scales. Only a very few lungfish have survived to this day, and the ray-finned, having gone through a period of slow evolution throughout the remainder of the Paleozoic era and the beginning of the Mesozoic, later, in the Mesozoic, experienced significant divergence and gave rise to modern bony fish (Teleostei).

  The lobe-finned fish, which were the ancestors of terrestrial vertebrates, almost died out by the end of the Paleozoic and, as previously believed, disappeared completely at the end of the Mesozoic. However, in 1939 and 1952 off the east coast South Africa live representatives of the crossopterygium about 1.5 m long were caught.

  The upper part of the Devonian was marked by the appearance of the first terrestrial vertebrates - amphibians called stegocephali (meaning "covered heads"). These animals, whose skulls were covered with a bony shell, are in many respects similar to lobe-finned fish, differing from them mainly in the presence of limbs, and not fins.

  The Devonian is the first period that is characterized by true forests. During this period, ferns, club mosses, ferns and primitive gymnosperms flourished - the so-called "seed ferns". It is believed that insects and centipedes arose in the Late Devonian.

• Carboniferous period [show] .

  At this time, large swampy forests were widespread, the remains of which gave rise to the main coal deposits of the world. The continents were covered with low-lying swamps overgrown with ferns, common ferns, seed ferns and broad-leaved evergreens.

  

  

  The first reptiles, called whole-skull and similar to the amphibians that preceded them, appeared in the second half of the Carboniferous period, flourished in the Permian - the last period of the Paleozoic - and died out at the beginning of the Mesozoic era. It is not clear what the most primitive of the reptiles known to us Seymouria (named after the city in Texas near which its fossils were found) was - an amphibian, ready to turn into a reptile, or a reptile that had just crossed the border separating it from amphibians .

  One of the main differences between amphibians and reptiles is the structure of the eggs they lay. Amphibians lay their eggs, covered with a gelatinous membrane, in the water, and reptiles lay their eggs, covered with a strong shell, on the ground. Since the eggs of Seymouria have not been preserved, we may never be able to decide which class this animal should be placed in.

  Seymouria was a large slow lizard-like form. Its short, stump-like legs extended horizontally away from the body, like a salamander's, instead of squeezing closer and going straight down to form column-like supports for the body.

  During the Carboniferous period, two important groups winged insects - the ancestors of cockroaches, reaching 10 cm in length, and the ancestors of dragonflies, some of which had a wingspan of 75 cm.

• Permian period [show] .

  

  

  The last period of the Paleozoic was characterized by major changes in climate and topography. Continents have risen all over the globe, so that the shallow seas that covered the region from Nebraska to Texas have dried up, leaving behind a salty desert. At the end of the Permian, widespread folding, known as the Hercynian orogeny, took place, during which a large mountain range from Nova Scotia to Alabama was uplifted. This range was originally higher than the modern Rocky Mountains. At the same time, other mountain ranges were forming in Europe.

  Enormous ice sheets extending from the Antarctic closed most of southern hemisphere, stretching in Africa and Brazil almost to the equator.

  North America was one of the few areas that did not undergo glaciation at this time, but even here the climate became much colder and drier than it had been during most of the Paleozoic era. Many Paleozoic organisms, apparently, could not adapt to climate change and died out during the Hercynian orogeny. Due to the cooling of water and the reduction of space suitable for life, as a result of the drying up of shallow seas, even many marine forms have become extinct.

  From the primitive whole-cranial during the Late Carboniferous and Early Permian, that group of reptiles developed from which mammals are believed to have descended in a straight line. These were pelycosaurs - predatory reptiles with a more slender and lizard-like body than those of whole-skull.

  In the late Permian, another group of reptiles, the therapsids, probably developed from pelycosaurs, possessing several other mammalian features. One of the representatives of this group - Cynognathus (reptile with a "dog jaw") was a slender, light animal about 1.5 m long, with a skull intermediate in character between that of a reptile and a mammal. Its teeth, instead of being conical and identical, as is characteristic of reptiles, differentiated into incisors, canines and molars. Since we have no information about the soft parts of the animal, whether it was covered with scales or hair, whether it was warm-blooded or cold-blooded, and whether it suckled its young, we call it reptile. However, if we had more complete data, it might have to be considered a very early mammal. Therapsids, widespread in the late Permian, were replaced by many other reptiles at the beginning of the Mesozoic.

Mesozoic era (time of reptiles). The Mesozoic era, which began about 230 million years ago and lasted about 167 million years, is divided into three periods:

1. Triassic
2. Jurassic
3. chalky

During the Triassic and Jurassic periods, most of the continental regions were raised above sea level. In the Triassic, the climate was dry, but warmer than in the Permian, and in the Jurassic, it was warmer and more humid than in the Triassic. The trees of the famous Stone Forest in Arizona have been around since the Triassic period.

During the Cretaceous period, the Gulf of Mexico, expanding, flooded Texas and New Mexico, and in general the sea gradually moved towards the continents. In addition, vast swamps have developed in the area stretching from Colorado to British Columbia. At the end of the Cretaceous period, the interior of the North American continent experienced further subsidence, so that the waters of the Gulf of Mexico basin joined with the waters of the Arctic basin and divided this continent into two parts. The Cretaceous ended with a great uplift called the Alpine orogeny, during which the Rocky Mountains, the Alps, the Himalayas, and the Andes arose, and which caused volcanic activity in western North America.

The evolution of reptiles . The emergence, differentiation and finally extinction of a great number of reptiles belonging to the six main branches are the most characteristic feature of the Mesozoic era. [show] .

The most primitive branch includes, in addition to the ancient whole-skull, turtles that arose in Perm. Turtles have developed the most complex (among land animals) shell; it consists of plates of epidermal origin, fused with the underlying ribs and breastbone. With this protective device, both sea turtles and tortoises survived from pre-dinosaur times with only a few structural changes. The legs of turtles, which extend from the body in a horizontal direction, which makes it difficult and slow to move, and their skulls, which do not have holes behind the eye sockets, were inherited unchanged from the ancient whole-cranial ones.

The second group of reptiles, coming with relatively few changes from the ancestral whole-skull, are lizards, the most numerous among living reptiles, as well as snakes. Lizards have for the most part retained a primitive type of movement with horizontally diverging legs, although many of them can run quickly. In most cases, they are small, but the Indian monitor reaches 3.6 m in length, and some fossil forms are 7.5 m long. Cretaceous mosasaurs were sea lizards that reached 12 m in length; they had a long tail used for swimming.

During the Cretaceous period, snakes evolved from lizard ancestors. The essential difference between snakes and lizards is not the loss of legs (some lizards also lack legs), but certain changes in the structure of the skull and jaws that allow snakes to open their mouths wide enough to swallow animals larger than themselves.

The representative of the ancient branch, somehow managed to survive to this day in New Zealand, is the tuatara (Shpenodon punctatum). It shares several features with its cotylosaur ancestors; one such feature is the presence of a third eye at the top of the skull.

The main group of Mesozoic reptiles were the archosaurs, the only living representatives of which are alligators and crocodiles. At some early point in their evolution, archosaurs, then 1.5 meters long, adapted to walking on two legs. Their front legs shortened, while their hind legs lengthened, strengthened and greatly changed their shape. These animals rested and walked on all four legs, but in critical circumstances they reared up and ran on two hind legs, using their rather long tail as a balance.

Many different specialized forms evolved from early archosaurs, some of which continued to walk on two legs while others returned to walking on all fours. These descendants include phytosaurs - aquatic, alligator-like reptiles common in the Triassic; crocodiles, which formed in the Jurassic and replaced phytosaurs as aquatic forms, and finally pterosaurs, or flying reptiles, which included animals the size of robins, as well as the largest animal ever flying, Pteranodon, with a wingspan of 8 m

There were two types of flying reptiles; some had a long tail, equipped with a tail blade at the end, others had a short tail. Representatives of both types, apparently, fed on fish and probably flew long distances over water in search of food. Their legs were not adapted for standing, and therefore it is assumed that they, like bats, rested in a suspended state, clinging to some kind of support.

Of all the branches of reptiles, dinosaurs are the most famous, which means "terrible lizards" in translation. They were divided into two main types: ornithischians and lizards.

Saurischia (lizards) first appeared in the Triassic and continued to exist until the Cretaceous. The early lizards were fast, predatory, rooster-sized, bipedal forms that probably preyed on lizards and primitive mammals that had already appeared. During the Jurassic and Cretaceous, this group showed an increasing trend in size, culminating in the giant Cretaceous predator Tyrannosaurus Rex. Other Saurischia, which appeared in the late Triassic, switched to plant foods, again began to walk on four legs, and during the Jurassic and Cretaceous gave rise to a number of giant forms that led an amphibious lifestyle. These largest four-legged animals that have ever lived include brontosaurs up to 20 m long, diplodocus, which reached a length of over 25 m, and brachiosaurus, the largest of all, whose weight is estimated at 50 tons.

Another group of dinosaurs, the Ornitischia (Ornithischians), were herbivores, probably from the very beginning of their evolution. Although some of them walked on their hind legs, most moved on all four legs. Instead of missing front teeth, they developed a strong horny sheath, similar to a bird's beak, which in some forms was wide and flat, like ducks (hence the name "duck-billed" dinosaurs). This type is characterized by webbed feet. Other species developed large armored plates that protected them from predatory lizards. The ankylosaurus, which is called the "reptile tank", had a wide flat body covered with bone plates and large spikes protruding from the sides.

Finally, some Cretaceous ornithischians developed bony plates around their heads and necks. One of them, Triceratops, had two horns above the eyes and a third above the nasal region - all up to almost 1 m long.

Two other groups of Mesozoic reptiles that differ both from each other and from dinosaurs are marine plesiosaurs and ichthyosaurs. The first were characterized by an extremely long neck, which was more than half the length of the animal. Their body was wide, flat, resembling the body of a turtle, and their tail was short. Plesiosaurs swam with flipper-like limbs. Often they reached 13-14 m in length.

Ichthyosaurs (lizard fish) were similar in appearance to fish or whales, with a short neck, a large dorsal fin, and a shark-type tail. They swam with swift tail movements, using their limbs only as controls. It is believed that ichthyosaur cubs were born alive, hatching from an egg in the mother's body, since adults were too specialized and could not go to land to lay eggs, and reptile eggs drown in water. The finding of juvenile skeletons inside the abdominal cavity of adult fossils supports this theory.

At the end of the Cretaceous, many reptiles died out. They obviously could not adapt to the significant changes in environmental conditions caused by the Alpine orogeny. As the climate became colder and drier, many plants that served as food for herbivorous reptiles disappeared. Some herbivorous reptiles were too bulky to move on land when the swamps dried up. The smaller, warm-blooded mammals that had already appeared had an advantage in the competition for food, and many of them even fed on reptile eggs. The extinction of many reptiles was probably the result of the combined action of a number of factors or any one factor.

Other directions of evolution in the Mesozoic . Although reptiles were the dominant animals in the Mesozoic, many other important organisms also developed at this time. [show] .

In the Mesozoic, the number and diversity of gastropods and bivalves increased. Sea urchins reached highest point of its development.

In the Triassic, mammals arose, and in the Jurassic, bony fish and birds arose.

Most modern orders of insects appeared in the early Mesozoic.

During the early Triassic, seed ferns, cycads, and conifers were the most common plants, but by the Cretaceous, many other forms resembling modern species appeared - fig trees, magnolias, palm trees, maples and oaks.

From the Jurassic time, magnificent imprints of the most ancient species of birds have been preserved, on which even the outlines of feathers are visible. This creature, called Archeopteryx, was about the size of a crow and had rather weak wings, jaws armed with teeth, and a long reptilian tail covered with feathers.

Fossils of two other birds, Hesperornis and Ichthyornis, have been found in the Cretaceous deposits. The first is an aquatic diving bird that has lost the ability to fly, and the second is a strong flying bird with reptilian teeth, about the size of a dove.

Modern toothless birds formed at the beginning of the next era.

Cenozoic era (time of mammals). The Cenozoic era can justifiably be called the time of birds, the time of insects, or the time of flowering plants, since the development of all these organisms is no less characteristic of it than the development of mammals. It covers the period from the Alpine orogeny (about 63 million years ago) to the present day and is divided into two periods - the Tertiary, which lasted about 62 million years, and the Quaternary, which includes the last 1-1.5 million years.

• Tertiary period. This period is subdivided into five epochs: Paleocene, Eocene, Oligocene, Miocene and Pliocene. The rocky mountains formed at the beginning of the Tertiary period were already strongly eroded by the Oligocene, as a result of which the North American continent acquired a gently undulating relief.

  In the Miocene, another series of uplifts created the Sierra Nevada mountains and new ranges in the Rocky Mountains, which led to the formation of deserts in the west. The climate in the Oligocene was milder than at present, so that palm trees spread as far north as Wyoming.

  The uplift, which began in the Miocene, continued into the Pliocene and, combined with the glaciations of the Pleistocene time, led to the extinction of many pre-existing mammals and other animals. The final uplift of the Colorado Plateau, which formed the Grand Canyon, almost ended in a short time Pleistocene and modern eras.

  The oldest fossils of true mammals date back to the Late Triassic, and in the Jurassic, there were already four orders of mammals, all of which were the size of a rat or a small dog.

  The earliest mammals (monotrems) were oviparous animals, and their only representatives that have survived to this day are the platypus and the needle-covered echidna living in Australia. Both of these forms have a coat, and they feed their young with milk, but they also lay eggs, like turtles. The ancestral egg-laying mammals, of course, must have been different from the specialized platypus and echidna, but the fossil record of these ancient forms is incomplete. Living monotremes could only last so long because they lived in Australia, where until recently there were no placental mammals, so they had no one to compete with.

  In the Jurassic and Cretaceous, most mammals were already highly organized enough to produce live young, although in the most primitive of them - the marsupials - the young are born underdeveloped and must remain for several months in the pouch on the mother's abdomen, where the nipples are located. Australian marsupials, like monotremes, did not meet competition from more adapted placental mammals, while on other continents this competition led to the extinction of marsupials and monotremes; therefore, in Australia, marsupials, as a result of divergent development, gave rise to many different forms, outwardly resembling some placentals. There are marsupial mice, shrews, cats, moles, bears, and one kind of wolf, as well as a number of forms that have no placental parallels, such as kangaroos, wombats, and wallabies.

  During the Pleistocene, giant kangaroos and rhinoceros-sized wombats lived in Australia. Opossums are more similar to primitive ancestral marsupials than any of these more specialized forms; they are the only marsupials found outside of Australia and South America.

  Modern highly organized placental mammals, which include humans, characterized by the birth of live young capable of independent existence, descended from insectivorous arboreal ancestors. Fossils of this ancestral form, found in the Cretaceous deposits, show that it was a very small animal, like the living shrew. Some of these ancestral mammals retained an arboreal way of life and, through a series of intermediate forms, gave rise to primates - monkeys and humans. Others lived on the ground or underground, and during the Paleocene all other mammals living today are descended from them.

  Primitive Paleocene mammals had conical reptilian teeth, five-fingered limbs, and a small brain. Also, they were plantigrade, not digitigrade.

  During the Tertiary period, the evolution of herbaceous plants, which served as food, and forests, which sheltered animals, was the most important factor influencing the change in the structure of the body of mammals. Along with a tendency to increase in size, the development of all mammals showed a bias towards an increase in the relative size of the brain and changes in teeth and legs. When new, more adapted forms appeared, primitive mammals died out.

  Although fossil remains of both marsupials and placentals were found in the Cretaceous deposits, the discovery of highly developed mammals in the Early Tertiary deposits was rather unexpected. Whether they really arose at this time or whether they existed earlier in the highlands and simply did not survive as fossils is not known.

  In the Paleocene and Eocene, the first predators, called creodonts, originated from primitive insectivorous placentals. In the Eocene and Oligocene, they were replaced by more modern forms, which over time gave rise to living predators, such as cats, dogs, bears, weasels, as well as pinniped marine predators - seals and walruses.

  

  One of the best-known fossil predators is the saber-toothed tiger, which became extinct only recently, in the Pleistocene. It had extremely long and sharp upper fangs, and the lower jaw could swing down and to the side so that the fangs pierced the prey like sabers.

  Large herbivorous mammals, in most cases with hooves, are sometimes combined into one group called ungulates. However, they are not a single natural group, but consist of several independent branches, so that a cow and a horse, despite the fact that they both have hooves, are no more related to each other than each of them is to a tiger. The molars of ungulates are flattened and enlarged, which facilitates the grinding of leaves and grass. Their legs became long and adapted to the fast running necessary to escape from predators.

  The oldest ungulates, called Condylarthra, appeared in the Paleocene. They had a long body and a long tail, flat grinding molars, and short legs ending in five toes with a hoof on each. A group analogous to primitive predators - creodonts, were primitive ungulates called wintatheria. In the Paleocene and Eocene, some of them reached the size of an elephant, while others had three large horns extending from the top of the head.

  The paleontological record of several evolutionary lines of ungulates - horses, camels and elephants - is so complete that it is possible to trace the entire development of these animals from small primitive five-fingered forms. The main direction of evolution in ungulates was towards an increase in the overall size of the body and a decrease in the number of fingers. Ungulates early fell into two groups, one of which is characterized by an even number of fingers and includes cows, sheep, camels, deer, giraffe, pigs and hippos. Another group is characterized by an odd number of fingers and includes horses, zebras, tapirs and rhinos.

  The development of elephants and their recently extinct relatives - mammoths and mastodons - can be traced back centuries to the Eocene ancestor, which was the size of a pig and did not have a trunk. This primitive form, called Moeritherium, was close to the trunk, from which branched, in addition, such dissimilar forms as hyraxes (a small marmot-like animal found in Africa and Asia) and a sea cow.

  Whales and dolphins are descended from Eocene cetacean forms called zeiglodonts, and these latter in turn are believed to have descended from creodonts.

  The evolution of bats can be traced back to winged animals that lived in the Eocene and were descendants of primitive insectivores.

  The evolution of some other mammals - rodents, rabbits and edentulous (anteaters, sloths and armadillos) - is less well known.

• Quaternary period (human time). The Quaternary period, which covers the last 1-1.5 million years, is usually divided into two epochs - Pleistocene and modern. The latter began approximately 11,000 years ago, from the moment the last glacier retreated. The Pleistocene is characterized by four ice ages, separated by intervals when the glaciers retreated. At the time of maximum distribution, ice sheets occupied almost 10 million square meters in North America. km, extending south to the Ohio and Missouri rivers. The Great Lakes, which have been plowed by moving glaciers, have drastically changed their outlines many times and from time to time connected with the Mississippi. It has been estimated that in the past, when the Mississippi collected water from the lakes, to Duluth in the west and to Buffalo in the east, its discharge was more than 60 times its present day. During the Pleistocene glaciations, such an amount of water was removed from the sea and turned into ice that the sea level dropped by 60-90 m. England and the European mainland.

  Plants and animals of the Pleistocene era were similar to those of our time. It is sometimes difficult to distinguish Pleistocene deposits from Pliocene deposits as well, since the organisms they contain are similar both to each other and to modern forms. During the Pleistocene, after the appearance of primitive man, many mammals became extinct, including the saber-toothed tiger, the mammoth, and the giant ground sloth. The Pleistocene also saw the extinction of many plant species, especially forest species, and the appearance of numerous herbaceous forms.

  The fossil record leaves no doubt that living species evolved from pre-existing other species. This chronicle is not equally clear for all lines of evolution. Plant tissues are in most cases too soft to give good fossils, and intermediate forms that serve as links between different types animals were, obviously, forms devoid of a skeleton, and no traces of them remained. For many evolutionary lines, in particular for vertebrates, successive stages of development are well known. Other lines have gaps that future paleontologists will have to fill.

Each of us sometimes worries about such questions that are difficult to find answers. These include understanding the meaning of one's existence, the structure of the world, and much more. We believe that everyone once thought about the development of life on Earth. The eras that we know are very different from each other. In this article, we will analyze in detail, and how exactly its evolution took place.

catarchean

Katarchaeus - when the earth was lifeless. There were volcanic eruptions everywhere, ultraviolet radiation and no oxygen. The evolution of life on Earth began its countdown precisely from this period. Due to the interaction of chemicals that have enveloped the earth, properties characteristic of life on Earth begin to form. However, there is another opinion. Some historians believe that the Earth has never been empty. In their opinion, the planet exists as long as life on it.

The katarchean era lasted from 5 to 3 billion years ago. Studies have shown that during this period the planet did not have a core and the earth's crust. An interesting fact is that at that time the day lasted only 6 hours.

archaeus

The next era after the Catarchean is the Archean (3.5-2.6 billion years BC). It is divided into four periods:

• neoarchean;
• mesoarchean;
• paleoarchaean;
• eoarchean.

It was during the Archean that the first simple microorganisms arose. Few people know, but the deposits of sulfur and iron that we mine today appeared during this period. Archaeologists have found the remains of filamentous algae, the age of which allows them to be attributed to the Archean period. At this time, the evolution of life on Earth continued. heterotrophic organisms appear. Soil is formed.

Proterozoic

The Proterozoic is one of the longest periods of the Earth's development. It is divided into the following steps:

• mesoproterozoic;
• neoproterozoic.

This period is characterized by the appearance of the ozone layer. Also, it was at this time, according to historians, that the volume of the world ocean was fully formed. The Paleoproterozoic era included the Siderian period. It was in it that the formation of anaerobic algae occurred.

Scientists note that it was in the Proterozoic that global glaciation occurred. It lasted for 300 million years. This situation is also characterized glacial period which was much later. During the Proterozoic, sponges and fungi appeared among them. It was during this period that deposits of ore and gold were formed. The Neoproterozoic era is characterized by the formation of new continents. Scientists note that all the flora and fauna that existed during this period is not the ancestor of modern animals and plants.

Paleozoic

Scientists study geological eras Earth and the development of the organic world long enough. In their opinion, the Paleozoic is one of the most significant periods for our modern life. It lasted about 200 million years and is divided into 6 time periods. It was during this era of the development of the Earth that land plants began to form. It is worth noting that during the Paleozoic period, animals came to land.

The Paleozoic era was studied by many famous scientists. Among them are A. Sedgwick and E. D. Phillips. It was they who divided the era into certain periods.

Paleozoic climate

Many scientists have done research to find out the Era, as we said earlier, could last long enough. It is for this reason that during one chronology for certain area The Earth at different times can have a completely opposite climate. So it was in the Paleozoic. At the beginning of the era, the climate was milder and warmer. There was no zoning as such. The percentage of oxygen constantly increased. The water temperature was between 20 degrees Celsius. Over time, zonation began to appear. The climate became hotter and more humid.

By the end of the Paleozoic, as a result of the formation of vegetation, active photosynthesis began. A more pronounced zoning appeared. Climatic zones formed. This stage has become one of the most important for the development of life on Earth. The Paleozoic era gave impetus to the enrichment of the planet with flora and fauna.

Flora and fauna of the Paleozoic era

At the beginning of the Paleosian period, life was concentrated in water bodies. In the middle of the era, when the amount of oxygen reached high level, the development of land began. Its very first inhabitants were plants, which first performed their vital activity in shallow water, and then moved to the shore. The first representatives of the flora that mastered the land are psilophytes. It is worth noting that they did not have roots. The process of formation of gymnosperms is also referred to the Paleozoic era. Tree-like plants also appeared. In connection with the appearance of flora on earth, animals gradually began to appear. Scientists suggest that herbivorous forms were the first to arise. The process of development of life on Earth lasted for quite a long time. Era and living organisms are constantly changing. The first representatives of the fauna are invertebrates and spiders. Over time, insects with wings, ticks, mollusks, dinosaurs, reptiles appeared. IN late period The Paleozoic saw significant climatic changes. This led to the extinction of some animal species. According to preliminary estimates, about 96% of the inhabitants of the water and 70% of the land died.

Minerals of the Paleozoic era

It is with the Paleozoic period that the formation of many minerals is associated. Rock salt deposits began to form. It is also worth emphasizing that some oil basins originate precisely from the beginning of the formation of coal strata, which account for 30% of the total. Also, the formation of mercury is associated with the Paleozoic period.

Mesozoic

The next after the Paleozoic was the Mesozoic. It lasted about 186 million years. The geological history of the Earth began much earlier. However, it was the Mesozoic that became the era of activity, both climatic and evolutionary. The main boundaries of the continents were formed. Mountain building has begun. There was a division of Eurasia and America. It is believed that it was in the climate that was the warmest. However, at the end of the era, the ice age began, which significantly changed the flora and fauna of the earth. Natural selection has taken place.

Flora and fauna in the Mesozoic era

The Mesozoic era is characterized by the extinction of ferns. Gymnosperms and conifers predominate. Angiosperms are formed. It was in the Mesozoic period that the fauna flourished. The most developed are reptiles. In this period, there were a large number of their subspecies. Flying reptiles appear. Their growth continues. By the end, some representatives weigh about 50 kilograms.

In the Mesozoic, the development of flowering plants gradually begins. By the end of the period, a cold snap sets in. The number of subspecies of near-aquatic plants is decreasing. Gradually, invertebrates also die out. It is for this reason that birds and mammals appear.

According to scientists, birds originated from dinosaurs. They associate the emergence of mammals with one of the subclasses of reptiles.

Cenozoic

Cenozoic is exactly the era in which we live today. It began about 66 million years ago. At the beginning of the era, the division of the continents was still taking place. Each of them was dominated by its own flora, fauna and climate.

Cenozoic is distinguished by a large number of insects, flying and marine animals. Mammals and angiosperms predominate. It was at this time that all living organisms evolve strongly and are distinguished by a large number of subspecies. Grains appear. The most important transformation is the emergence of Homo sapiens.

Human evolution. Initial stages of development

The exact age of the planet cannot be determined. Scientists have been arguing about this topic for a long time. Some believe that the age of the Earth is 6,000 thousand years, others that it is more than 6 million. Guess we'll never know the truth. The most important achievement of the Cenozoic era is the appearance of Homo sapiens. Let's take a closer look at exactly how this happened.

There are a large number of opinions regarding the formation of mankind. Scientists have repeatedly compared a wide variety of sets of DNA. They came to the conclusion that monkeys have the most similar organism to humans. It is impossible to prove this theory to the end. Some scientists argue that the human and pig bodies are also quite similar.

Human evolution is visible to the naked eye. At first, biological factors were important for the population, and today social factors are important. Neanderthal, Cro-Magnon, Australopithecus and others - all of which our ancestors went through.

Parapithecus is the first stage in the development of modern man. At this stage, our ancestors existed - monkeys, namely chimpanzees, gorillas and orangutans.

Australopithecus was the next stage of development. The first found remains were in Africa. According to preliminary data, their age is about 3 million years. Scientists examined the find and came to the conclusion that australopithecines are quite similar to modern humans. The growth of representatives was quite small, about 130 centimeters. The mass of Australopithecus was 25-40 kilograms. The guns, most likely, they did not use, since they were never found.

A skilled man was similar to Australopithecus, but, unlike them, he used a primitive tool. His hands and knuckles were more developed. It is believed that a skilled person is our direct ancestor.

Pithecanthropus

The next stage of evolution was Pithecanthropus - Homo erectus. Its first remains were found on the island of Java. According to scientists, pithecanthropes lived on the Earth about a million years ago. Later, the remains of Homo erectus were found in all corners of the planet. Based on this, we can conclude that Pithecanthropes inhabited all continents. The body of a erect human was not much different from the modern one. However, there were minor differences. Pithecanthropus had a low forehead and well-defined brow ridges. Scientists have found that an upright person led an active lifestyle. Pithecanthropes hunted and made simple tools. They lived in groups. So it was easier for Pithecanthropes to hunt and defend themselves from the enemy. Finds in China allow us to conclude that they also knew how to use fire. Pithecanthropes developed abstract thinking and speech.

Neanderthal

Neanderthals lived about 350 thousand years ago. Found about 100 remains of their life. The Neanderthal skull was domed. Their height was about 170 centimeters. They had a fairly large physique, well-developed muscles and good physical strength. They had to live in the Ice Age. It is thanks to this that Neanderthals learned to sew clothes from leather and constantly keep fire. There is an opinion that Neanderthals lived only on the territory of Eurasia. It is also worth noting that they carefully processed the stone for the future tool. The Neanderthals often used wood. From it they created a tool of labor and elements for dwellings. However, it is worth noting that they were quite primitive.

Cro-Magnon

Cro-Magnons were tall, which was about 180 centimeters. They had all the signs of modern man. Over the past 40 thousand years, their appearance has not changed at all. After analyzing the human remains, scientists concluded that average age Cro-Magnons was about 30-50 years old. It is worth noting that they created more complex types of weapons. Among them are knives and harpoons. The Cro-Magnons fished, and therefore, in addition to the standard set of weapons, they also created new ones for comfortable fishing. Among them are needles and much more. From this we can conclude that the Cro-Magnons had a well-developed brain and logic.

A reasonable man built his dwelling out of stone or dug it out of the ground. The nomadic population created temporary huts for greater convenience. It is also worth noting that the Cro-Magnons tamed the wolf, turning it over time into a watchdog.

Cro-Magnons and art

Few people know that it was the Cro-Magnons who formed the concept that we now know as the concept of creativity. On the walls of a large number of caves were found cave drawings made by Cro-Magnons. It is worth emphasizing that the Cro-Magnons always left their drawings in hard-to-reach places. Perhaps they performed some kind of magical role.

The Cro-Magnon people had a variety of drawing techniques. Some clearly traced the images, while others scratched them. Cro-Magnons used colored paints. Predominantly red, yellow, brown and black. Over time, they even began to carve human figures. You can easily find all the exhibits found in almost any archaeological museum. Scientists note that the Cro-Magnons were quite developed and educated. They liked to wear jewelry made from the bones of the animals they had killed.

There is quite an interesting opinion. Previously, it was believed that the Cro-Magnons ousted the Neanderthals in an unequal struggle. Scientists today think otherwise. They believe that for a certain amount of time, Neanderthals and Cro-Magnons lived side by side, but the weaker ones died from a sharp cold snap.

Summing up

The geological history of the Earth began many millions of years ago. Each era has contributed to our modern life. We often do not think about how our planet has evolved. Studying the information about how our Earth was formed, it is impossible to stop. The history of the evolution of the planet can bewitch everyone. We strongly recommend that we take care of our Earth, if only so that after millions of years the history of our existence will have someone to study.

The thesis about the evolution of the Earth, as an exceptional object of its kind in the cosmos, occupies the main step. In view of this, geological time becomes a special numerical-evolutionary characteristic. The comprehension of this time is engaged in science, which bears the definition of Geochronology, that is, the geological account of time. The above specialized science is divided into two types: absolute geochronology and relative geochronology.

Absolute geochronology carries out activities to determine the absolute age of rocks. This age is transmitted in units of time, namely, in millions of years.

The key link in establishing this age is the rate of decay of isotopes of radioactive components. This speed is extremely constant and is free from the saturation of physical and chemical currents. Age notation is organized in ways that are related to nuclear physics. Minerals, which have radioactive components in their composition, give rise to a closed structure during the device crystal lattices. It is in such a structure that the process of accumulation of elements of radioactive decay takes place. Therefore, if you have information about the speed of the presented process, you can find out how old the mineral is. For example, the half-life of radium is about 1590 years. And the final decay of this element will occur in a period of time that is ten times longer than the half-life. Nuclear geochronology has the main methods, namely: lead, potassium-argon, rubidium-strontium and radiocarbon.

It was the presented methods of nuclear geochronology that contributed to the establishment of the age of the planet and the time of eras and periods. At the beginning of the 20th century, P. Curie and E. Rutherford introduced a different method of setting the time, which was called radiological. Relative geochronology carries out the activity of determining the relative age of rocks. That is, which accumulations in the earth's crust are younger and which are ancient.

Relative geochronology specializes in such theses as "early, middle and late age". A number of techniques for identifying the relative age of rocks have scientific justification. These methods can be divided into two groups. These groups are called paleontological and non-paleontological. Paleontological methods occupy a leading position, as they are more multifunctional and are applied on a wide front. Of course, there are exceptions. Such a rare case is the lack of natural accumulations in the rocks. Use the presented method when studying fragments of extinct ancient organisms. It should be noted that each rock layer is characterized by a specific set of natural remains. The Englishman W. Smith discovered a certain chronology in the age characteristics of the breeds. Namely, the higher the layer is, the younger it is in age. Consequently, the content of microorganism residues in it will be an order of magnitude higher. Also, W. Smith owns the first geological map of England. On this map, the scientist divided the rocks by age.

Non-paleontological methods for determining the relative age of rocks are used in cases where there are no organic remains in the rocks under study. In this case, there are stratigraphic, lithological, tectonic and geophysical methods. For example, when using the stratigraphic method, it is possible to establish the chronology of the formation of layers at their standard occurrence, namely, those layers that lie below will be more ancient.

The establishment of the chronology of the formation of rocks is carried out by relative geochronology, while the specific determination of age in units of time is carried out by absolute geochronology. The purpose of geological time is to discover the temporal chronology of geological phenomena.

Geological table

In order to establish the age criteria for rocks, scientists use a wide variety of methods. Therefore, it was expedient to create a highly specialized scale for ease of use. Geological time according to this scale is divided into time intervals. A certain segment is characterized by a specific stage in the structure of the earth's crust and the formation of living organisms. The presented scale has a name - geochronological table. It has such subgroups as eon, era, period, epoch, century, time. It should be noted that each group is characterized by a certain set of savings. Such a collection, in turn, is called a stratigraphic complex, which also has a number of types, namely: eonoteme, group, system, department, stage, zone. For example, the system belongs to the stratigraphic category, and the time group of the geochronological department belongs to its characteristic subgroup, which is called the era. As a consequence, there are two scales: stratigraphic and geochronological. The stratigraphic school is used when accumulations in rocks are studied. Since any geological processes are carried out on the planet at any time. The geochronological scale is used to set relative time. Since the scale was approved, its structure has undergone many changes.

To date, the most voluminous stratigraphic category is eonotemes. It is divided into Archean, Proterozoic and Phanerozoic. In the geochronological scale, these classes are subject to categories of diverse activities. Based on the time of existence on Earth, scientists identified two eonotems: Archean and Proterozoic. It is these eonotemes that comprised about eighty percent of the entire time. The remaining Phanerozoic eonoteme is noticeably smaller than the previous eons, since it covered only about five hundred and seventy million years. This eonoteme is divided into three main classes: Paleozoic, Mesozoic and Cenozoic.

The names of eonotems and classes come from the Greek language:

• Archeos - the most ancient;
• Proteros - primary;
• Paleos - ancient;
• Mezos - medium;
• Kainos - new;

From the word form "zoikos", which has the definition of "life", the word "zoi" was formed. Based on this word formation, scientists have identified the era of life on Earth. For example, the Paleozoic era means the era of ancient life.

Eras and periods

Based on the geochronological table, experts divided the history of the planet into five geological eras. The above eras received the following names: Archean, Proterozoic, Paleozoic, Mesozoic, Cenozoic. Also, era data is divided into periods. The number of these time intervals is equal to twelve, which apparently exceeds the number of eras. The time span of these stages is from twenty to one hundred million years. The last period of the Cenozoic era is not completed, since its time period is about two million years.

Archean era. This era began its existence after the formation and structuring of the earth's crust on the planet. By this time period, there were already rocks on the planet and the processes of erosion and accumulation of precipitation had begun. This era lasted for about two billion years. It is the Archean era that scientists consider the longest in time. During its course, volcanic processes were active on the planet, depths were raised, which contributed to the formation of mountains. Unfortunately, most of the fossils were destroyed, but some general data about this era still survive. In the rocks that existed in the Archean era, scientists have found pure carbon. Experts believe that these are modified remains of living organisms. In view of the fact that the amount of graphite indicates the amount of living matter, there was quite a lot of it in this era.

Proterozoic era. According to the time characteristic, this is the next period, which contains one billion years. During this epoch, precipitation accumulated and one global glaciation occurred. Fossils that were found in the mountain strata of this time are the main witnesses that life existed and went through stages of evolution. The remains of jellyfish, mushrooms, algae and much more were found in the rock layers.

Palaeozoic. This era is divided into six time periods:

• Cambrian;
• Ordovician;
• Silur;
• Devonian;
• Carbon/Coal;
• Perm / Perm;

The time period of the Paleozoic era covers three hundred and seventy million years. During this period, representatives of all classes of the animal world appeared. Only birds and mammals were missing.

Mesozoic era. Experts have identified three stages:

• Triassic;

This period covers a time span of one hundred and sixty-seven million years. During the first two periods, the main part of the continents carried out a rise above sea level. Climatic conditions gradually changed and became warmer. There is a popular stone forest in Arizona that has existed since the Triassic period. During the last period, a gradual rise of the sea occurs. The North American continent was completely submerged, as a result of which the Gulf of Mexico was connected to the Arctic basin. The end of the Cretaceous period is characterized by the fact that large uplifts of the earth's crust occurred. So the Rocky Mountains, the Alps, the Himalayas, the Andes appeared.

Cenozoic era. This period continues to this day. Experts divide it into three periods:

• Paleogene;
• Neogene;
• Quaternary;

The last period is characterized by special features. During this period, the final formation of the planet took place. Set apart New Guinea and Australia. The two Americas have merged. This time period was identified by J. Denoyer in 1829. The main feature is that a person appeared.

It is during this period that all of humanity lives today.