There is a whole complex of sciences that study the main stages of the development of life on Earth, they all consider this issue in many ways, because this is a fundamental problem of natural science. The significance of paleontology, which studies the remains of plants and animals of past eras, is very important; it is directly related to the study of the evolution of the world.

This science studies the main ones by reconstructing the appearance, external similarities and differences, the way of life of prehistoric, already extinct animals and plants, and also determines the approximate time of existence of a particular species. But paleontology could not exist as a separate science without many others that support it; this science is at the intersection of biological and geological disciplines. The main stages of the development of life on Earth are recreated with the help of disciplines such as:

historical geology;
stratigraphy;
paleography;
comparative anatomy;
paleoclimatology and many others.

All of them are interconnected; without one, the others cannot exist.

Geological time

To single out the main stages in the development of life on Earth, it is necessary to have an idea of such a concept as geological time. How did people manage to identify some time stages? The whole secret lies in the study of rocks. The fact is that the rocks that arose at a later time are superimposed on top of those that existed earlier. And the age of these layers can be determined by studying the fossils remaining in them.

Among all their diversity, the so-called guiding fossils stand out, which are the most numerous and widespread. Unfortunately, with the help of rocks it is impossible to establish the absolute age, but even here scientists do not stop, extracting this knowledge from volcanic rocks. As you know, they arise from magma. This is how the main stages of the development of life on earth are distinguished.

Briefly, the process of determining the absolute age of volcanic rocks looks like this: igneous rocks contain some elements, if you determine their content in the rock, then you can accurately determine the absolute age of the rock. Of course, errors are possible, but they do not exceed five percent. In addition, the age of our planet is also determined, all scientists adhere to their figures, but the generally accepted value is five billion years. Now we will highlight the main stages, which will be a good helper in this case.

Eras, eras and periods

In total, paleontologists distinguish five stages or, in other words, eras, each of which is divided into periods, all of which consist of eras, and the last of centuries. The Archean and Proterozoic eras are the most ancient times, covering about three billion years. They are distinguished by the complete absence of vertebrates and terrestrial plants, which appear in the "era of ancient life", which spans more than three hundred million years. Next comes the "era of middle life", the Mesozoic (one hundred and seventy-five million years), its distinctive features are the development of reptiles, birds, mammals, plants, both flowering and angiosperms.

The latest, fifth, era is the Cenozoic, also called the "era of new life", it began seventy million years ago, and we are still living in it. characterized by the rapid development of mammals and the appearance of man. Now we have analyzed the stages of the development of life on Earth briefly, we propose to consider each era separately.

Archean era

This stage covers the period from three thousand nine hundred to two thousand six hundred million years ago. Part of the sedimentary rocks, that is, formed with the help of particles of the aquatic environment, remained in Africa, Greenland, Australia and Asia. All of them contain:

biogenic carbon;
stromatolites;
microfossils.

At the same time, the origin of the latter in this era is not entirely clear; for example, in the Proterozoic they are associated with cyanobacteria. In the Archean era, all organisms were classified as prokaryotes, and sulfates, nitrates, nitrites, and so on served as a source of oxygen. All existing organisms on the planet outwardly resembled mold films, mainly located at the bottom of reservoirs, in volcanic areas.

Proterozoic era

It is important to mention that this era is also divided into three periods. In addition, this is the longest period of our history (approximately two million years). If we consider the turn of this era and the Archean, then it was during this period that our planet changed a lot, the land and water expanses were redistributed. The earth was an icy desert, but at the end of this period, the percentage of oxygen reached one percent, which contributed to sustainable life. unicellular organisms bacteria and algae evolved.

At the end of the Proterozoic, multicellular animals formed, this period is also called the “age of jellyfish”. Single-celled organisms are being replaced by multicellular ones, which qualitatively change the composition of the atmosphere, which contributes to the development of life on our planet.

Paleozoic

It includes as many as six periods, the first half is called the early Paleozoic, and the second - late. The early and late Paleozoic differ in animal and plant life.

At the first stage, evolution can be traced exclusively in underwater world, land settlement began only in the Devonian, which belongs to the late Paleozoic.

Mesozoic era

We are now moving into a most interesting era, rich in mystery and diversity of life, evolving over a period of some one hundred and eighty-five million years. As can be seen from the table, it is also divided into three periods. The Cretaceous, compared with the Jurassic and Triassic, is the longest (seventy-one million years).

As for the climate, it all depends on the location of the continents. Differences from our climate are that:

it was much warmer than today;
there were no temperature differences between the equators and the poles.

In addition, the air was humid, which contributed to the rapid development of living organisms.

If we turn to fauna, then the most unique group is the well-known dinosaurs. They have taken a dominant position over other forms of life due to the structure of their body, physiological data and reaction.

So, analyzing the question of what are the main stages in the development of life on Earth, we have identified five stages. To complete the picture, it remains to consider one more. We suggest you get started right now.

Cenozoic era

This new era which continues to this day. The continents have acquired a modern look, the last dinosaurs have disappeared, plants and animals that are quite familiar to us predominate on Earth. We briefly reviewed the main stages in the development of life on Earth, analyzed all the stages separately, and our goal has been achieved.

You already know that there are many hypotheses trying to explain the origin and development of life on our planet. And although they offer different approaches to solving this problem, most of them suggest that there are three evolutionary stages: chemical, prebiological and biological evolution(Fig. 87).

At the stage of chemical evolution, abiogenic synthesis took place organic monomers, low molecular weight organic compounds.

At the second stage, the stage of prebiological evolution, biopolymers were formed, which were combined into protein-nucleic acid-lipoid complexes (scientists called them differently: coacervates, hypercycles, probionts, progenots, etc.), which, as a result of selection, formed an ordered metabolism and self-reproduction.

At the third stage, the stage of biological evolution, the first primitive living organisms entered into biological natural selection and gave rise to all the diversity of organic life on Earth.

Most scientists believe that Prokaryotes were the first primitive living organisms. They fed on the organic matter of the "primordial broth" and received energy in the process of fermentation, that is, they were anaerobic heterotrophs. With an increase in the number of heterotrophic prokaryotic cells, the stock of organic compounds in primary ocean was depleted. Under these conditions, organisms capable of autotrophy, i.e., of synthesizing organic matter from inorganic due to oxidation and reduction reactions.

Apparently chemosynthetic bacteria were the first autotrophic organisms.

The next step was the development of photosynthesis - a complex of reactions using sunlight. As a result of photosynthesis, oxygen began to accumulate in the earth's atmosphere. This was a prerequisite for the emergence of aerobic respiration in the course of evolution. The ability to synthesize more ATP during respiration allowed organisms to grow and reproduce faster, as well as complicate their structures and metabolism.

Most scientists believe that eukaryotes evolved from prokaryotic cells. There are two most accepted hypotheses for the origin of eukaryotic cells and their organelles.

The first hypothesis links the origin of the eukaryotic cell and its organelles with the process of invagination of the cell membrane (Fig. 88).

The hypothesis of the symbiotic origin of the eukaryotic cell has more supporters. According to this hypothesis, the mitochondria, plastids, and basal bodies of the cilia and flagella of the eukaryotic cell were once free-living prokaryotic cells. They became organelles in the process of symbiosis (Fig. 89). This hypothesis is supported by the presence of intrinsic RNA and DNA in mitochondria and chloroplasts. The RNA structure of mitochondria is similar to the RNA of purple bacteria, and the RNA of chloroplasts is closer to that of cyanobacteria. Data received in last years as a result of studying the structure of RNA in various groups of organisms, it may be forced to reconsider established views.

Comparing the nucleotide sequence in ribosomal RNA, scientists came to the conclusion that all living organisms can be classified into three groups: eukaryotes, eubacteria and archaebacteria (the last two groups are prokaryotes).

Since the genetic code in all three groups is the same, it was hypothesized that they have a common ancestor, who was called "progenot" (i.e. progenitor).

It is assumed that eubacteria and archaebacteria could have descended from the progenote, and the modern type of eukaryotic cell, apparently, arose as a result of a symbiosis of an ancient eukaryote with eubacteria (Fig. 90).

Written work with cards:

1. Three stages in the development of life on Earth.

2. What energy was used and used by living organisms of the Earth?

3. Evolution of cellular life forms.

4. Hypothesis of the origin of the eukaryotic cell by symbiogenesis.

Board card:

1. What happened at the stage of chemical evolution?

2. What happened at the stage of prebiological evolution?

3. What happened at the stage of biological evolution?

4. What type of food were the primary living organisms?

5. How did the original prokaryotes get their energy?

6. Who were the first autotrophic prokaryotes?

7. What were the consequences of the emergence of photoautotrophic organisms?

8. How did mitochondria appear according to the symbiogenesis hypothesis?

9. How did chloroplasts appear according to the symbiogenesis hypothesis?

10. Which organisms appeared first - oxidizing bacteria or cyanobacteria?

Test:

1. What happened at the stage of chemical evolution:

1. Prokaryotes appeared.

2. What happened at the stage of prebiological evolution:

1. Prokaryotes appeared.

2. Abiogenic synthesis of organic substances took place.

3. Biopolymers were formed and combined into coacervates.

4. Probionts appeared with a matrix type of heredity, capable of self-reproduction.

3. What happened at the stage of biological evolution:

1. Prokaryotes appeared.

2. Abiogenic synthesis of organic substances took place.

3. Biopolymers were formed and combined into coacervates.

4. Probionts appeared with a matrix type of heredity, capable of self-reproduction.

4. The first organisms that appeared on Earth, according to the method of nutrition, were:

1. Anaerobic heterotrophic prokaryotes.

2. Aerobic heterotrophic prokaryotes.

3. Anaerobic autotrophic prokaryotes.

4. Aerobic autotrophic prokaryotes.

5. How primary prokaryotes received energy:

1. Due to oxygen oxidation of finished organic substances, respiration.

2. Due to oxygen-free oxidation of finished organic substances.

3. Used the energy of light for photosynthesis.

4. We used the energy that was released during the oxidation of inorganic substances.

6. Who were the first autotrophic prokaryotes:

1. Photoautotrophs.

2. Chemoautotrophs.

**7. What are the consequences of the emergence of photoautotrophic organisms:

1. To the appearance of breath.

2. To the appearance of glycolysis.

3. To the appearance of free oxygen in the atmosphere.

4. To the appearance of plants.

8. How did mitochondria appear according to the symbiogenesis hypothesis:

9. How did chloroplasts appear according to the hypothesis of symbiogenesis:

1. As a result of symbiosis with oxidizing bacteria.

2. As a result of symbiosis with cyanobacteria.

3. As a result of symbiosis with purple sulfur bacteria.

4. As a result of symbiosis with green sulfur bacteria.

archean eon

Earth is the only planet solar system, which formed the conditions favorable for the emergence and development of life. Life on Earth originated at the bottom of the warm, shallow seas of the Katarchean, where complex polymers were formed, capable of synthesizing proteins, providing them with a fairly long self-preservation. The evolution of these primary microorganisms gave rise in them to the ability to synthesize organic molecules from inorganic. Most effective way turned out to be photosynthesis - the production of organic matter from carbon dioxide and water.

The first photosynthesizing plants were apparently microscopic blue-green algae and bacteria. These organisms were distinguished by the absence of a nucleus and were called prokaryotes (Procaryota - pre-nuclear) and the special position of DNA, which is located freely in cells, not separated from the cytoplasm by a nuclear membrane. All other organisms have a nucleus surrounded by a membrane and sharply limited from the cytoplasm. Such organisms are called eukaryotes (Eycaryota - nuclear).

The oldest reliable traces of the vital activity of organisms called stromatolites were found in Australia, their age is 3.5 billion years, and also found in chert of the Fig Tree series of the Swaziland system (Barbeton) in the Transvaal, whose age is 3.1-3.4 billion years . Almost as ancient (more than 2.9 billion years) are the calcified waste products of blue-green algae - loose rounded formations - oncolites (stromatolites - attached to the bottom). The Archean eon is the time of prokaryotes - bacteria and blue-green algae, the only traces of life in the distant past. It began 4.5 billion years ago and ended 2.6 billion years ago.

Proterozoic eon

The Proterozoic eon is divided by a boundary of 1650 Ma into Early Proterozoic and Late Proterozoic, which is called the Riphean. In the early Proterozoic, mainly prokaryotes were developed - blue-green algae, traces of the vital activity of which in the form of stromatolites and oncolites are already known in many parts of the world. At the turn of 2 billion years, in the middle of the Early Proterozoic, the level of oxygen in the atmosphere, apparently, approached the modern one, as evidenced by the formation of the largest deposits of iron in the geological history, for the formation of which, as is known, free oxygen was needed, converting peroxide forms of iron into oxide ones, which reduced the mobility of iron and led to massive precipitation of a suspension of iron oxide hydrates into the SiO2 * nH2O complex, which then transformed into ferruginous quartzites-jaspilites. These are the largest iron deposits of the Krivoy Rog basin and the Kursk magnetic anomaly in Russia, Lake Superior in North America and India.

According to R.E. Folinsby notes that the noticeable qualities of free oxygen appeared about 2.2 billion years ago. In the Riphean, the production of free oxygen by algae increased steadily: the abundance of algal structures makes it possible to distinguish several subdivisions in it.

Evolution took the next step - there were organisms that consume oxygen. Traces of burrowing animals and tubes of worms were found in the rocks of the Upper and Middle Riphean. In the Vendian period, the upper Riphean, the abundance and level of development of organisms brings them closer to the Phanerozoic. Numerous imprints of various non-skeletal animals have been found in the Vendian deposits: sponges, jellyfish, annelids, and arthropods. Their remains are represented by imprints of soft tissues.

Phanerozoic eon

The Paleozoic era, covering more than half of the Phanerozoic, lasted more than 340 million years and is divided into two major stages: the Early Paleozoic, which began as early as the Late Riphean and Vendian, consisting of the Cambrian Ordovician and Silurian periods, and the Late Paleozoic, including the Devonian, Carboniferous and Permian periods.

The Cambrian period lasted 90 million years and is divided into three epochs. Its lower boundary passes at the turn of 570 Ma, and the upper one - 480 Ma (according to new data). The organic world of the Cambrian is notable for its considerable diversity: the most widely developed archeocyanates, brachiopods, trilobites, graptolites, sponges, and conodonts. Three-segmented forms of trilobites evolved especially rapidly, which already possessed a calcareous shell and learned to curl up, protecting the soft abdomen. A large number of their leading forms arose, which made it possible to dissect the Cambrian deposits in detail. The Cambrian brachiopods, which had chitin-phosphate shells, were primitive, without locks. An important group for the division and correlation of deposits are graptolites. Currently, more than 100 species of animals and algae are known for the Cambrian.

The Ordovician period lasted 4 million years and is divided into three epochs. At that time, marine basins occupied the largest area in the Phanerozoic, so the rapid flowering of marine fauna and flora continued. Trilobites and graptolites reach maximum development. There are four-beam corals, pelecypods and the first cephalopods - endoceratites. Among the brachiopods, castle varieties appear and the number of their genera reaches 200. At the same time, stalked echinoderms appear: sea lilies, blastoids, cystoids, crinoids. Conodonts play an important role in stratigraphy. In the Ordovician (and possibly even in the Cambrian), the so-called armored fish appear - small fish-like bottom animals without jaws and fins, covered with a shell of thick plates on the head and scales on the body. At the end of the Ordovician, a rather extensive glaciation was observed in places on Earth.

The Silurian period lasted 30 million years and is divided into two epochs. The seas are again expanding their areas, which is possibly due to the end of glaciation and the melting of glaciers. Groups of organisms that arose earlier continue to develop, with the exception of endoceratitis, which die out by the beginning of the period, and cystoids, which disappear in its middle. Real cartilaginous fish have already appeared - first armored, and then shellless sharks, which still live today. The first land animals, similar to modern scorpions, in which lungs were formed, originated from the huge predatory gill-breathing (class of crustaceans) gigantostraks. In the late Silurian, the first terrestrial higher plants appeared - psilophytes. Thus, the most significant event of the early Paleozoic is the appearance of the skeletal fauna and the "exit" of representatives of the plant and animal world to land.

The Devonian period lasted 55 million years and is divided into three epochs. The main event of this period is the "exit" to the land of many representatives of the animal and flora. In the Early Devonian, the species diversity of trilobites sharply decreases, graptolites and some classes of echinoderms disappear. Many guiding forms of hinge brachiopods appear. Since the early Devonian, ammonoids, four-beam corals, large foraminifera, and attached echinoderms (sea lilies) have been widely distributed. True bony fish have already been widely developed, giving rise to three different branches: ray-finned, lung-breathing, and lobe-finned.

From Devon dawn begins organic world on land: large scorpions and the first amphibians (amphibians) appear. They are called stegocephals, that is, armor-headed, since their head was covered with protective bone plates. In the Middle Devonian, many groups of higher plants arise: arthropods, lycopods, ferns, and gymnosperms.

The Carboniferous period lasted 65 million years and is divided into three epochs. This period is distinguished by a warm, humid climate, which caused a lush dawn of vegetation confined to swampy areas of land, within which huge masses of peat formed, which gradually turned into brown coal and then into bituminous coal during coalification. Extensive forests consisted of fomadic trees up to 50 m high - tree-like horsetails, club mosses, ferns, lepidodenrons, sigillaria, calamites. Cordaites, gingk and conifers appear in the middle of the Carboniferous.

In the Upper Carboniferous, the first reptiles appeared - Seimurians and Cotylosaurs, which retained a continuous skull cover, like amphibians. Ancient stromatopores, phaptolites, trilobites, jawless fish-like, armored fish, and psilophytes are disappearing from plants. Glaciation begins at the end of the Late Carboniferous.

The Permian period lasted 55 million years and is divided into two epochs. The regression of the sea, which began in the Carboniferous, increases more and more, which leads to the dominance of the land. The Late Carboniferous glaciation expands and covers the southern hemisphere. The climate of the northern hemisphere was arid, hot, in the equatorial zone - humid. During this period, the tropical fauna is replaced by gymnosperms, mainly conifers, the first cycads appear. All the main groups of the Carboniferous fauna and flora continue to live in the Permian, but by the end of the Permian period, many Paleozoic organisms die out: four-beam corals, the main species of brachiopods, bryozoans, crinoids, trilobites, many species of fish, amphibians, etc.; from plants - cordaites, tree-like ferns and club mosses, that is, at the turn of the Paleozoic and Mesozoic, a change in the animal and plant world took place everywhere. Thus, the late Paleozoic is characterized by major changes in the organic world, which outlines a clear boundary for the end of the Paleozoic era.

Mesozoic era. Triassic. The duration of the Mesozoic era is 183 million years. The Triassic period lasted 40 million years and is divided into three stages. On the border of the Paleozoic and Mesozoic eras, the renewal of the organic world took place. The Early Triassic was dominated by continental conditions, which gave way in the Middle Triassic to extensive marine transgression, which reached its maximum at the beginning of the Late Triassic. The Triassic climate was mostly warm and dry. New groups of animals appeared - ammonites, belemnites, pelecypods, six-ray corals. Along with the invertebrates, reptiles developed rapidly, especially dinosaurs, which gave a wide variety of different forms; the first aquatic reptiles appeared: plesiosaurs, pliosaurs and ichthyosaurs.

On land in the Triassic, the first mammals appeared - small animals the size of a rat. Among the land animals, reptiles reigned supreme, which were distinguished by their huge size and unusual shapes (brachiosaurs up to 24 m long, diplodocus, brontosaurs reached a length of 30 m, their weight was 35 tons, and some individuals - up to 80 tons). Reptiles have already begun to master the airspace. In the USA, in the west of Texas, the remains of an ancient bird were found, whose age is 225 million years, that is, it lived in the Triassic period.

The Jurassic period lasted 69 million years and is divided into three epochs. The beginning of the Jurassic period is characterized by the spread of the continental regime on the ancient Precambrian platforms. From the Middle Jurassic, as a result of the subsidence of the Precambrian platforms, extensive transgressions developed, which in the Late Jurassic turned into one of the greatest transgressions on the globe due to the formation of the Atlantic and Indian Oceans. The climate of the Jura is considered warm.

Among the representatives of the marine fauna, new species of ammonites and belemnites appear. Giant dinosaurs continue to develop, flying lizards and archaeornis, which were the size of a crow, had toothy jaws, weak wings with claws at the ends and long tails with numerous vertebrae, covered with feathers. Among the rich vegetation, ferns, ginkgos and cycads were developed.

The Cretaceous period lasted 70 million years (the longest after the Cambrian period) and is divided into two epochs. At the beginning of the Cretaceous, new transgressions develop after a short-term regression of the sea at the end of the Jurassic. All groups of the Jurassic fauna continue to develop: six-ray corals, bivalve mollusks with thick shells. Giant ammonites appear, the shell diameter of which sometimes reaches 3 m. Belemnites develop widely, sea urchins, bony fish. Large flying lizards appeared with a wingspan of up to 8 m. The appearance of the first toothless birds was noted.

At the very beginning of the Lower Cretaceous, Jurassic forms of plants still continue to exist, but during the entire Cretaceous period, great changes occur in the composition of the flora. At the end of the Lower Cretaceous, angiosperms begin to play a significant role. And from the very beginning of the Upper Cretaceous era, they already occupy a dominant position. The appearance of vegetation begins to take on modern forms: willow, birch, plane tree, oak, beech and true flowering plants appear.

At the end of the Cretaceous period, a radical restructuring of the organic world takes place. Ammonites and the main groups of belemnites disappear in the seas, dinosaurs disappeared on land, their flying and swimming forms. The extinction of the dinosaurs remained the largest and most dramatic event in the history of the organic world, the causes of which have been many hypotheses.

In the end, it can be noted that the change in the organic world, apparently, is associated with significant transformations in the distribution of continents and oceans and the peculiarity of climatic features.

Cenozoic era. Paleogene period. The duration of the Cenozoic era is 65 million years. The Paleogene period lasted 42 million years and was divided into three epochs: Paleocene, Eocene and Oligocene. In the Paleogene period, the outlines of the continents approach the modern ones. At the beginning of the Paleocene, as a result of downward vertical movements, the transgression of the sea began to develop, reaching a maximum by the end of the Eocene - the beginning of the Oligocene. At the end of the Oligocene, with a change in the sign of vertical movements, a regression of the sea developed, which led to the drying of the platforms. There are big changes in the animal world. Belemnites, ammonites, terrestrial and marine reptiles are disappearing. Among the protozoa, foraminifers play an important role - nummulites, which reach large sizes. Six-ray corals and echinoderms were widely distributed. Bony fish have acquired a dominant position in the seas.

From the beginning of the Paleogene, only snakes, turtles and crocodiles remained among the reptiles, and the spread of mammals began, at first primitive, and then more and more highly organized: the first paired and equids, proboscis and marsupials. Monkeys appear, take on the modern appearance of a bird.

The vegetation was distinguished by the predominant distribution of angiosperms, the development of tropical flora climate zone within central Europe- palm trees, cypresses and a temperate climate zone with cold-loving flora - oak, beech, plane tree and conifers, common to the north.

The Neogene period lasted 21 million years and is divided into two epochs: Miocene and Pliocene. After the establishment of the continental regime within the Precambrian platforms at the end of the Oligocene, it persisted throughout the Neogene. In the Neogene, as a result of the completion of Alpine folding, an extended mountain-folded belt was formed, which began from the Strait of Gibraltar and ended with the Pamirs, the Hindu Kush and the Himalayas.

The formation of high extended mountain ranges contributed to the intensification of cooling, which began as early as the Oligocene. In the Pliocene, the increasing cooling caused the formation of first mountain-valley, and then sheet glaciers. Glaciers appeared in Greenland, Iceland, Canada, on the islands of the Arctic archipelago, in Scandinavia, South America and other places. The period of the great Quaternary glaciations began, which led to a reduction in the range of heat-loving fauna and flora and a change in their nature.

Animals adapted to the conditions of a cold climate appear: mammoths, bears, wolves, and big-horned deer. The vertebrate fauna takes on the appearance of modern animals.

Placental mammals flourish: real predators, bears, mastodons, bulls, and at the end of the Neogene - elephants, hippos, hipparions and real horses (hypparion fauna).

Due to the fact that large areas were occupied by land with grassy vegetation, insects were widely developed. Great apes and a wide variety of birds appeared. The appearance of vegetation came close to modern, with a clear division into warm and cold-loving floras.

The Quaternary period began 1.7 million years ago and continues to this day. This period is divided into three epochs: Eopleistocene, Pleistocene and Holocene. In the Quaternary, powerful glaciation covered the continents of the northern hemisphere: most of Europe, the Asian part of Russia and North America, where glaciers covered the entire northern half of the continent, descending along the river valley. Mississippi south of 37° N. sh. The thickness of the ice sheet reached 4 km, and the total area of glaciers was 67%, while now it is 16% of the total land area.

Significant changes took place in the animal world of this period: typical representatives of the hipparion fauna died out and were replaced by animals that adapted to life in the cold climate of the tundra and forest-tundra spaces that arose as a result of glaciation - hairy mammoths, woolly rhinos, bison, tours, deer, etc. .

The most significant event of the Quaternary period was the appearance of man. Primates are considered the ancestor of man, as well as monkeys.

The first human ancestor, who lived about 12 million years ago, is Ramapithecus. The first hominid, who already walked on two legs, was Australopithecus (i.e., the southern monkey), lived 6.0-1.5 million years ago. In 1972, on the shore of the lake. Rudolph discovered the remains of a skilled man (Homohabilis), who could make primitive tools. Its age is 2.6 million years. Then, about a million years ago, Homo erectus appeared, who had already learned to use fire. Then there is Pithecanthropus, Heidelberg man, Sinanthropus, united under the general name of archanthropes.

About 250 thousand years ago, an early Homo sapiens appeared in Europe, from which the Neanderthals, who were supplanted by the Cro-Magnons 40-35 thousand years ago, originated. These were people with a modern body structure and skull, which are the ancestors of modern man, which appeared about 10 thousand years ago.

It is difficult to overestimate the importance of the general chronological scale created by many generations of geologists. different countries and continents and reflecting in stages the entire geological history of our planet.

Finishing the presentation of the history of the development of the organic world, one should dwell on the genetic concept that establishes the natural boundaries of its evolution and links them with the stages of endogenous activation of the earth.

Biotic crises - mass extinctions of animals and plants are correlated in a certain way with ice ages and phases of the Earth's endogenous activity - degassing of the Earth's core substance, activation of volcanic activity and increased basaltic magmatism.

The first biotic crisis - the extinction of some animals and plants and the emergence of new species - occurred in the Upper Proterozoic, which ended with four catastrophic glaciations in the interval 850-600 million years ago. The end of the last, most grandiose ice age (600 million years ago) is characterized by the appearance of the Ediacaran fauna found in Ediacara, in southern Australia, the soft-bodied representatives of which suddenly disappeared at the border of the Proterozoic and Paleozoic, giving way to the Cambrian fauna - archaeocyates, trilobites, brachiopods. The correlation of this crisis with the formation of clay deposits in China enriched in iridium, copper and chalcophile elements is noteworthy.

Subsequent major biotic crises occurred at the border of the Paleozoic and Mesozoic. 90% of all marine animals disappeared. At this boundary, the formation of clays (Italy, San Antonio) with increased concentrations of Ir, Cr, Ni, Co, Sc, Ti, sometimes Cu and chalcophile elements is also noted. The boundary of the Triassic and Jurassic was marked by the mass extinction of animals and the formation of clays enriched with iridium, phosphorus, rare earth elements, as well as V, Cr, Ni, Ti, Zn, As, etc. The end of the Mesozoic era ended with the mass extinction of dinosaurs, ammonites, and the widespread black shales , basalt covers and deposits enriched with iridium. And the last biotic crisis of the beginning of the Holocene (about 10 thousand years ago) ended with warming after the glaciation and the extinction of mammoths.

A.A. Marakushev notes that all boundaries of biotic catastrophes are marked by the global distribution of black shales, the formation of which is associated with periodic intensification of the spreading of the World Ocean and intense hydrogen degassing of the liquid core of the Earth, marked by geochemical anomalies and anomalous accumulation of iridium in sediments. Black shale formations reflect the catastrophic transformations of the Earth, synchronized with the peaks of global diastrophisms (billion years).

Periods of degassing are characterized by the penetration of hydrogen into the hydrosphere and atmosphere, which causes the destruction of the protective ozone layer of the Earth, accompanied by glaciation and subsequent biotic catastrophes.

Another manifestation of the activation of the Earth's endogenous dynamics is the periodic appearance of explosive ring structures (astroblemes) on platforms, which also mark the boundaries of geological stages.

The regularities of the cyclical nature of the geological history of the Earth can be summarized in the following sequence. Periodic manifestations of the Earth's endogenous activation are determined by impulses of hydrogen degassing of the Earth's liquid core in the zone of mid-ocean ridges and the periodic formation of explosive ring structures (astroblemes) on platforms. The degassing of the liquid core is accompanied by volcanic explosive eruptions, the formation of thick tuffaceous strata, outpouring of mantle basalts, and inversion magnetic poles, the formation of black shales and the appearance of geochemical anomalies. Hydrogen degassing destroys the protective ozone layer, which leads to periodic glaciations followed by mass extinction of animals and plants - biotic catastrophes.

Dinosaur skeletons have been found throughout human history, but our ancestors mistook them for the bones of dragons, griffins, and other mythical creatures. When scientists first encountered dinosaur remains in 1677, the director of one of British museums, Robert Plot, identified the pieces of bone as a fragment of the femur of a giant man. Myths about antediluvian giants developed for several hundred more years, until scientists learned how to accurately restore fossil remains and determine their age. The science of fossil animals is being improved today, applying latest methods research. Thanks to them, scientists can accurately restore the appearance of amazing creatures that walked the earth millions of years ago.

Exceptionally rich material for the development of evolutionary ideas was provided by the science of paleontology, which studies the history of life from the remains of organisms that have been preserved in rocks and sediments (see Fig. 1). Paleontology has recreated the main chronology of events that occurred mainly in the last 700 million years, when the evolution of life on our planet was especially intensive.

This part of the history of the development of the Earth is usually divided into large intervals, which are called eras. Eras, in turn, are divided into smaller intervals - periods. Periods - for epochs and centuries. The era names are Greek origin. For example, Mesozoic - "middle life", Cenozoic - " new life". Each era, and sometimes even a period, has its own characteristics in the development of the animal and plant world ().

For the first 1.5 billion years after the formation of our planet, living organisms did not exist on it. This period is called katarchey (Greek "below the most ancient"). Education took place in the Katharchea earth's surface, there were active volcanic and mountain-building processes. Life arose on the border of the Katarchean and archean era. This is evidenced by the finds of traces of vital activity of microorganisms in rocks aged 3.5-3.8 billion years.

The Archean era lasted 900 million years and left almost no traces of organic life. The presence of rocks of organic origin: limestone, marble, carbon dioxide indicates the existence of bacteria and cyanobacteria, that is, prokaryotic organisms, in the Archean era (see Fig. 2). They lived in the seas, but, perhaps, went out on land as well. In Archaea, water is saturated with oxygen, and soil-forming processes take place on land.

Rice. 1

Rice. 2

It was in the Archean era that three major changes occurred in the development of living organisms: the emergence of the sexual process, the emergence of photosynthesis, and the emergence of multicellularity ().

The sexual process arose as a result of the fusion of two identical cells in flagellates, which are considered the most ancient unicellular. With the advent of photosynthesis, a single trunk of life was divided into two - plants and animals. And multicellularity led to a further complication of life: tissue differentiation, the emergence of organs and organ systems (see Fig. 3).

Rice. 3

In the Proterozoic era lasting 2 billion years, algae develop - green, brown, red (see Fig. 4), and fungi also appear.

Rice. 4

The ancestors of multicellular organisms may have been colonial organisms like modern colonial flagellates (see Fig. 5). And the first multicellular organisms were like modern sponges and corals (see Fig. 6).

Rice. 5

Rice. 6

Animal world of that period was represented by all types of invertebrates (see Fig. 7).

Rice. 7

It is believed that at the end of the Proterozoic era, primary chordates, a subtype of non-cranial, appeared, the only representative of which in the modern fauna is the lancelet (see Fig. 8).

Rice. 8

Bilateral symmetrical animals appear, sense organs develop, ganglions, the behavior of animals becomes more complicated (see Fig. 9).

Rice. 9

The Paleozoic era began 570 million years ago and was characterized by the most important evolutionary events in the history of the development of organic life on Earth (). At the beginning of this era, a significant part of the Earth's land was formed, the formation of the ozone screen ended, which made it possible for the first plants, rhyniophytes, to come to earth about 400 million years ago (see Fig. 10, 11). They, unlike algae, already possessed conductive, integumentary and mechanical tissues; allowing to exist in the conditions of the ground-air environment. Then the main groups of higher spore plants originated from rhinophytes: lycopods, horsetails and ferns, from which primary forests were formed () (see Fig. 12).

During the Carboniferous period, there was a major evolutionary upsurge in the development of terrestrial vegetation.

Rice. 10

Rice. eleven

Rice. 12

This period was characterized by a warm, humid climate. On Earth, huge terrestrial forests were formed, consisting of giant ferns, tree-like horsetails and club mosses from 15 to 20 m high.

They had a good conducting system, roots, leaves, but their reproduction was still associated with water. During this period, seed ferns grew, which developed seeds instead of spores (see Fig. 13). The appearance of seed plants was the largest aromorphosis in the history of the development of the Earth, since the reproduction of seed plants no longer depended on water. The embryo is located in the seed and is provided with a supply of nutrients.

Rice. 13

Since the end of the Carboniferous period, due to the active mountain-building process, the humid climate everywhere becomes dry. Tree ferns are dying out, leaving only their small forms in damp places. Seed ferns are also dying out. The forests of the Carboniferous period led to the formation of coal deposits.

Rice. 14

In the development of the animal world in the Paleozoic (see Fig. 14), the most important evolutionary events also took place. At the beginning of the era, the first vertebrates appeared - armored fish. They possessed an internal skeleton that gave them an advantage in movement compared to invertebrates. Cartilaginous and bony fish then evolved from armored fish (see Fig. 15). Among the bony fish, the lobe-finned fish stood out, from which the first terrestrial vertebrates originated about 300 million years ago.

Rice. 15

The most primitive terrestrial vertebrates are considered to be ancient amphibians - stegocephals, which lived in marshy places (see Fig. 16, 17). Stegocephals combined the signs of fish and amphibians ().

Rice. 16

Rice. 17

Animals of this period, like plants, lived in humid places, so they could not spread inland and occupy places remote from water bodies. With the onset of dry conditions at the end of the Carboniferous period, large amphibians disappear, only small forms remain in damp places.

Amphibians were replaced by reptiles (see Fig. 18). More protected and adapted to existence in a dry climate on land, all reptiles, unlike amphibians, have skin protected from drying out with horny scales. Their reproduction is no longer associated with water, and the eggs are protected by dense shells.

Rice. 18

The Mesozoic era began about 230 million years ago. Climatic conditions were favorable to further development life on our earth. Gymnosperms dominated on land at that moment, but about 140 million years ago, the first angiosperms, or flowering plants, already arose ().

The seas were dominated by cephalopods and bony fish (see Fig. 19). Giant lizards lived on land - dinosaurs, as well as viviparous ichthyosaurs, crocodiles, flying lizards (see Fig. 20, 21).

Rice. 19

Rice. 20

Rice. 21

But giant reptiles died out relatively quickly. At the beginning of the Mesozoic, about 200 million years ago, the first birds originated from a group of ornithischian reptiles (see Fig. 22), and the first mammals originated from a group of animal-like reptiles (see Fig. 23).

Rice. 22

Rice. 23

A high level of metabolism, warm-bloodedness, a developed brain allowed birds and mammals to occupy a dominant position on our planet.

The Cenozoic era began 67 million years ago and continues to the present day. After the Pleogen and Neogene, the third period of the era began - the Anthropogen, in which we now live.

During this era, the seas and continents took shape in their present form. In the Pleogen, angiosperms spread throughout the land and in freshwater reservoirs, active mountain-building processes took place, as a result of which the climate became colder. This has led to the replacement of evergreen forests by deciduous forests. In the anthropogen, the modern flora and fauna finally formed, a person arose ().

Paleontology

Paleontology is a science that studies the history of the development of life on Earth according to the remains, imprints and traces of the vital activity of ancient living organisms preserved in sedimentary rocks. Scientific paleontology arose at the end of the 18th century. Georges Leopold Cuvier is considered its founder (Fig. 24).

Rice. 24

For more than 200 years of its existence, paleontology has accumulated a huge amount of material about ancient plants and animals, many of which are completely different from modern life forms.

Paleontologists study not only the remains of ancient plants and animals, but also fossils, that is, the bodies or fragments of the bodies of ancient living organisms in which organic substances have been replaced by mineral salts over time. Paleontology also uses the methods of paleoecology and paleoclimatology to recreate the living conditions under which ancient organisms existed. Recently, paleontology has received a new development due to the fact that the methods of computed tomography, digital microscopy, and molecular biology have become available to it. With the help of these discoveries, it was possible to prove that life on our planet is much older than it seemed before.

Geochronology

For convenience of study and description, the entire history of the Earth is divided into certain periods of time. These intervals differ in duration, mountain building processes, climate, flora and fauna. In the geochronological record, these periods are characterized by different layers of sedimentary rocks with fossil remains preserved in them. The deeper the sedimentary layer lies, the older the fossil in it. The largest divisions of the geological record are eons. There are two eons: cryptozoic, which in Greek means "secret life", and phanerozoic - "manifest life". Eons are divided into eras. There are two eras in the Cryptozoic: the Archean and the Proterozoic. And in the Phanerozoic - three eras: Paleozoic, Mesozoic and Cenozoic. Eras are in turn divided into periods, which may have smaller subdivisions.

The importance of photosynthesis in the development of life on Earth

The appearance of autotrophic organisms on Earth led to gigantic changes in its development. First, the appearance and vital activity of plants led to the formation of free oxygen in the atmosphere of our Earth. The presence of free oxygen changed biochemical processes, which led to the death of many living organisms, for which free oxygen was fatally toxic. But, on the other hand, the presence of free oxygen in the atmosphere allowed living organisms to master the process of respiration, as a result of which much more energy is accumulated in the form of an ATP molecule. Such an energetically more favorable way of breathing allowed living organisms to subsequently master the land. In addition, under the influence of ultraviolet radiation, oxygen was converted into ozone. Thanks to this process, a protective ozone screen was formed, which does not allow hard ultraviolet radiation to reach the Earth. This was another reason why living organisms were able to go to land. In addition, autotrophs themselves have become more high-energy food for heterotrophs. The interaction of autotrophs and heterotrophs, their birth and death led to the most important process of the emergence of the biological cycle of substances. Thanks to this, the once lifeless shell turned into a biosphere inhabited by living organisms.

Bibliography

Mamontov S.G., Zakharov V.B., Agafonova I.B., Sonin N.I. Biology. General patterns. - M.: Bustard, 2009.
Pasechnik V.V., Kamensky A.A., Kriksunov E.A. Biology. Introduction to general biology and ecology. Textbook for 9 cells. 3rd ed., stereotype. - M.: Bustard, 2002.
Ponomareva I.N., Kornilova O.A., Chernova N.M. Fundamentals of General Biology. Grade 9: Textbook for students in grade 9. educational institutions / Ed. prof. I.N. Ponomareva. - 2nd ed., revised. - M.: Ventana-Graf, 2005.

Homework

List the sequence of eras in the development of the Earth.
What era are we living in?
Could our species not have dominated the Earth?
What happened to animals and plants that arose in the Mesozoic?

Biology. General biology. Grade 11. A basic level of Sivoglazov Vladislav Ivanovich

16. Development of life on Earth

Remember!

What is the study of paleontology?

What eras and periods in the history of the Earth do you know?

About 3.5 billion years ago, an era began on Earth biological evolution, which continues even now. The appearance of the Earth was changing: tearing apart single land masses, continents drifted, mountain ranges grew, islands rose from the depths of the sea, glaciers crawled in long tongues from the north and south. Many species have come and gone. Someone's history was fleeting, and someone remained almost unchanged for millions of years. According to the most conservative estimates, several million species of living organisms now live on our planet, and over the entire long history, the Earth has seen about 100 times more species Living creatures.

At the end of the XVIII century. paleontology arose - a science that studies the history of living organisms according to their fossil remains and traces of vital activity. The deeper the layer of sedimentary rocks with fossils, traces or prints, pollen or spores, the older these fossil organisms. Comparison of fossils of various rock layers made it possible to distinguish several time periods in the history of the Earth, which differ from each other in the features of geological processes, climate, the appearance and disappearance of certain groups of living organisms.

The largest time intervals into which the biological history of the Earth is divided are zones: Cryptozoic, or Precambrian, and Phanerozoic. The zones are divided into era. There are two eras in the Cryptozoic: Archean and Proterozoic; in the Phanerozoic, there are three eras: Paleozoic, Mesozoic, and Cenozoic. In turn, eras are divided into periods, and periods are divided into epochs, or departments. Modern paleontology, using the latest research methods, has recreated the chronology of the main evolutionary events, accurately dating the appearance and disappearance of certain species of living beings. Consider the stage-by-stage formation of the organic world on our planet.

Cryptozoic (Precambrian). This is the oldest epoch, which lasted about 3 billion years (85% of the time of biological evolution). At the beginning of this period, life was represented by the simplest prokaryotic organisms. In the oldest known sedimentary deposits on Earth archean era discovered organic substances, which, apparently, were part of the oldest living organisms. Fossilized cyanobacteria were found in rocks whose age is estimated by the isotope method at 3.5 billion years.

Life during this period developed in the aquatic environment, because only water could protect organisms from solar and cosmic radiation. The first living organisms on our planet were anaerobic heterotrophs, which assimilated organic matter from the "primordial broth". The depletion of organic reserves contributed to the complication of the structure of primary bacteria and the emergence of alternative ways of feeding - about 3 billion years ago, autotrophic organisms arose. major event Archean era was the emergence of oxygen photosynthesis. Oxygen began to accumulate in the atmosphere.

Proterozoic era began about 2.5 billion years ago and lasted 2 billion years. During this period, about 2 billion years ago, the amount of oxygen reached the so-called "Pasteur point" - 1% of its content in the modern atmosphere. Scientists believe that this concentration was sufficient for the appearance of aerobic unicellular organisms, a new type of energy processes arose - oxygen respiration. As a result of a complex symbiosis of different groups of prokaryotes, eukaryotes appeared and began to actively develop. The formation of the nucleus led to the emergence of mitosis, and later meiosis. Approximately 1.5–2 billion years ago, sexual reproduction arose. The most important stage in the evolution of wildlife was the emergence of multicellularity (about 1.3–1.4 billion years ago). Algae were the first multicellular organisms. Multicellularity contributed to a sharp increase in the diversity of organisms. It became possible to specialize cells, form tissues and organs, distribute functions between parts of the body, which further led to the complication of behavior.

In the Proterozoic, all the kingdoms of the living world were formed: bacteria, plants, animals and fungi. In the last 100 million years of the Proterozoic era, there was a powerful surge in the diversity of organisms: various groups of invertebrates arose and reached a high degree of complexity (sponges, coelenterates, worms, echinoderms, arthropods, mollusks). An increase in the amount of oxygen in the atmosphere led to the formation of an ozone layer that protected the Earth from radiation, so life could come to land. About 600 million years ago, at the end of the Proterozoic, fungi and algae came to land, forming the oldest lichens. At the turn of the Proterozoic and the next era, the first chordate organisms appeared.

Phanerozoic. The eon, consisting of three eras, covers about 15% of the total time of existence of life on our planet.

Palaeozoic began 570 million years ago and lasted about 340 million years. At that time, intensive mountain-building processes were going on on the planet, accompanied by high volcanic activity, glaciations succeeded each other, seas periodically advanced and retreated on land. In the era of ancient life (Greek palaios - ancient), 6 periods are distinguished: Cambrian (Cambrian), Ordovician (Ordovician), Silurian (Silurian), Devonian (Devonian), Carboniferous (Carboniferous) and Permian (Permian).

IN Cambrian And Ordovician the diversity of the animal world of the ocean increases, this is the heyday of jellyfish and corals. Ancient arthropods - trilobites - appear and reach a huge variety. Chordate organisms develop (Fig. 53).

Rice. 53. Fauna of the Paleozoic era

Rice. 54. The first sushi plants

IN Silurian the climate becomes drier, the land area increases - the single continent of Pangea. In the seas, the mass distribution of the first true vertebrates begins - jawless, from which fish later descended. The most important event of the Silurian is the emergence of spore plants - psilophytes (Fig. 54). Following the plants, ancient arachnids come to land, protected from dry air by a chitinous shell.

IN Devonian the diversity of ancient fish increases, cartilaginous fish (sharks, rays) dominate, but the first bony fish also appear. In shallow drying waters with insufficient oxygen, lungfish appear, which, in addition to gills, have air breathing organs - sac-shaped lungs, and lobe-finned fish with muscular fins with a skeleton resembling the skeleton of a five-fingered limb. From these groups originated the first terrestrial vertebrates - stegocephals (amphibians).

IN carbone on land, forests of tree-like horsetails, club mosses and ferns spread, reaching a height of 30–40 m (Fig. 55). It was these plants that, falling into tropical swamps, did not rot in a humid tropical climate, but gradually turned into coal, which we now use as fuel. In these forests, the first winged insects appeared, resembling huge dragonflies.

Rice. 55. Carboniferous forests

In the last period of the Paleozoic era - Permian- the climate became colder and drier, so those groups of organisms, the vital activity and reproduction of which were completely dependent on water, began to decline. The diversity of amphibians, whose skin constantly required moisture and whose larvae had a gill type of breathing and developed in water, is decreasing. Reptiles are the main land hosts. They turned out to be more adapted to the new conditions: the transition to pulmonary respiration allowed them to protect the skin from drying out with the help of horny covers, and the eggs, covered with a dense shell, could develop on land and protected the embryo from exposure environment. New species of gymnosperms are being formed and widely distributed, and some of them have survived to this day (ginkgo, araucaria).

Mesozoic era began about 230 million years ago, lasted about 165 million years and included three periods: Triassic, Jurassic and Cretaceous. In this era, the complication of organisms continued and the pace of evolution increased. For almost the entire era, gymnosperms and reptiles dominated on land (Fig. 56).

Triassic- the dawn of the dinosaurs; crocodiles and turtles appear. The most important achievement of evolution is the emergence of warm-bloodedness, the first mammals appear. The species diversity of amphibians is sharply reduced and seed ferns are almost completely dying out.

Cretaceous period characterized by the formation of higher mammals and true birds. Angiosperms appear and spread rapidly, gradually replacing gymnosperms and ferns. Some angiosperms that arose in the Cretaceous period have survived to this day (oaks, willows, eucalyptus, palm trees). At the end of the period there is mass extinction dinosaurs.

cenozoic era, which began about 67 million years ago and continues to the present. It is divided into three periods: the Paleogene (Lower Tertiary) and Neogene (Upper Tertiary), with a total duration of 65 million years, and the Anthropogenic, which began 2 million years ago.

Rice. 56. Fauna of the Mesozoic era

Rice. 57. Fauna of the Cenozoic era

Already in Paleogene the dominant position was occupied by mammals and birds. During this period, most modern orders of mammals are formed, the first primitive primates appear. On land, angiosperms (tropical forests) dominate, in parallel with their evolution, the development and increase in the diversity of insects.

IN Neogene the climate becomes drier, steppes are formed, and monocotyledonous herbaceous plants are widely distributed. The retreat of forests contributes to the appearance of the first great apes. Formed species of plants and animals close to modern.

Last Anthropogenic period characterized by a cooling climate. Four giant glaciations led to the appearance of mammals adapted to the harsh climate (mammoths, woolly rhinos, musk oxen) (Fig. 57). Land "bridges" arose between Asia and North America, Europe and the British Isles, which contributed to the widespread dispersal of species, including humans. Approximately 35-40 thousand years ago, before the last glaciation, people reached North America along the isthmus at the site of the current Bering Strait. At the end of the period began global warming, many species of plants and large mammals died out, modern flora and fauna formed. The largest event of the Anthropogen was the emergence of man, whose activity became the leading factor in further changes in the flora and fauna of the Earth.

Review questions and assignments

1. By what principle is the history of the Earth divided into eras and periods?

2. When did the first living organisms arise?

3. What organisms represented the living world in the Cryptozoic (Precambrian)?

4. Why did a large number of amphibian species become extinct during the Permian period of the Paleozoic era?

5. In what direction was the evolution of plants on land?

6. Describe the evolution of animals in the Paleozoic era.

7. Tell us about the features of evolution in the Mesozoic era.

8. What impact did extensive glaciations have on the development of plants and animals in the Cenozoic era?

9. How can you explain the similarities between the fauna and flora of Eurasia and North America?

Think! Execute!

1. What evolutionary advantages have plants received by switching to seed propagation?

2. Explain why the duration of different eras and periods varies significantly.

3. Using additional literature and Internet resources, get acquainted with various existing hypotheses about the reasons for the extinction of dinosaurs. Organize and lead a discussion on the topic "Why did the dinosaurs become extinct?".

4. What is the relationship between the development of tropical forests and the increase in the diversity of insects in the Paleogene?

5. Many students find it difficult to remember the sequence of eras and periods. To make it easier to remember, try to come up with abbreviations - words made up of syllables or the first letters of terms. For example, periods of the Mesozoic era - hold (Triassic, Jurassic, Cretaceous). You can also use another mnemonic technique: create a semantic phrase, the words in which begin with the first letters of the memorized terms.

Work with computer

Refer to the electronic application. Study the material and complete the assignments.

Repeat and remember!

Botany

Features of seed plants, which allowed them to occupy a dominant position in the plant world. The main feature of seed plants is reproduction using seeds. Seed formation - major achievement in the evolution of the plant world. The spore contains a minimum of nutrients and requires a combination of many favorable conditions for further development. Compared to it, the seed contains a significant supply of nutrients, and the sporophyte embryo inside the seed is reliably protected by dense covers. The maximum dehydration of seed tissues and the presence of protective covers ensure long-term viability of seeds.

Seed plants have internal fertilization. This is an important adaptation, since this type of fertilization does not depend on the presence of water. However, in this case, the need for motile spermatozoa equipped with flagella disappears. Indeed, with the exception of some gymnosperms, the male gametes of seed plants do not have flagella and are not capable of independent locomotion. Such immobile male gametes of plants are called sperm. How do immobile spermatozoa penetrate the egg? The development of the pollen tube, through which sperm is transported to the ovule, is another important acquisition of seed plants.

The characterization of the traits of seed plants, which allowed them to conquer the entire globe, will be incomplete if we do not recall such a feature as the complexity of the structure of conducting tissues. In angiosperms, the vessels of wood form the most perfect conducting system. They are a long hollow tube, consisting of a chain of dead cells - vessel segments, in the transverse walls of which there are large holes - perforations. Thanks to these holes, a quick and unhindered flow of water is ensured.

Zoology

Lungfish and lobe-finned fish appeared in the Devonian period. Currently lungfish- This is a small group of freshwater fish that combines primitive features of ancestral forms with progressive adaptations to living in oxygen-depleted tropical waters. The fins of these fish have the appearance of fleshy lobes covered with scales. With their help, fish can not only swim, but also move along the bottom. Breathing gills and lungs. On the ventral side of the esophagus there are 1-2 hollow outgrowths that act as lungs. In the heart, the division of the atrium and the formation of the second circle of blood circulation are planned. With a lack of oxygen in the water or during hibernation, breathing is only pulmonary. Modern representatives: one-lungs - Australian horntooth and two-lungs - scaly (African protopters and South American lepidosiren). Horntooths live in perennial reservoirs and do not hibernate. When the water bodies dry up, the flakes can burrow into the ground and hibernate for a long period (up to 9 months). The protopter even forms a capsule.

lobe-finned fish long considered an extinct group. In 1938, the only modern species was discovered - coelacanth (see Fig. 22), which lives in the region of the Comoros at a depth of about 1000 m. A feature of lobe-finned fish is the presence of muscles in the composition of the limbs and the dissection of their skeleton. In evolution, this became a prerequisite for the transformation of fins into five-fingered limbs. Ancient lobe-finned fish lived in fresh water and had double breathing: with a lack of oxygen, they rose to the surface and breathed air. Their development went in two directions: one branch gave rise to the ancestors of modern amphibians, and the other adapted to life in sea water. The modern coelacanth, unlike its ancestors, is not capable of breathing atmospheric oxygen, its large degenerated lung is filled with fat.

In the Silurian period of the Paleozoic era, arthropods came to land, becoming the first inhabitants of the land among animals. At present, the type of arthropods is the most numerous and diverse of all animal types, it unites over 1.5 million species. This is more than all other animal species. There is no doubt that the prosperity of this group of invertebrates is associated with the acquisition of a number of adaptations in the process of evolution. The most important acquisitions of the ancestors of modern arthropods were the following:

Strong outer skeleton, represented by a chitinous cuticle;

Segmented body divided into sections;

Movable jointed limbs.

The outer chitinous skeleton performs not only the function of mechanical protection. Its acquisition allowed marine arthropods to resist the forces of gravity when they landed and protected their bodies from drying out. And the chitinous outgrowths of the body walls of the thoracic segments, which turned into wings, allowed the insects to take possession of the land.

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