According to incomplete estimates of scientists, there are about 1.5 million species of animals and at least 500 thousand species of plants on Earth.
Where did these plants and animals come from? Have they always been like this? Has the Earth always been as it is now? These questions have long worried and interested people. Religious fictions that the churchmen preach that the Earth and everything that exists on it was created within a week by a supernatural being - God, cannot satisfy us. Only science, relying on facts, was able to find out the true history of the Earth and its inhabitants.
Much has been done to study the development of life by the brilliant English scientist Charles Darwin, the founder of scientific biology (Darwinism), the Frenchman Cuvier, the founder of paleontology, the great Russian scientists A.O. Kovalevsky, I.I. Mechnikov, V.O. Kovalevsky, K.A. Timiryazev, I.P. Pavlov and many others.
The history of human society, peoples, states can be studied by examining historical documents and objects of material culture (remnants of clothing, tools, dwellings, etc.). Where there is no historical data, there is no science. The researcher of the history of life on Earth, obviously, also needs documents, but they differ significantly from those with which the historian deals. The bowels of the earth are the archive in which the “documents” of the Earth's past and life on it have been preserved. In the earth's strata are the remains of ancient life, which show what it was like thousands and millions of years ago. In the bowels of the Earth, you can find traces of drops of rain and waves, the work of winds and ice; on the basis of rock deposits it is possible to reconstruct the contours of the sea, rivers, swamps, lakes and deserts of the distant past. Geologists and paleontologists who study the history of the Earth are working on these "documents."
The layers of the earth's crust are a huge museum of natural history. He surrounds us everywhere: on steep steep banks of rivers and seas, in quarries and mines. Best of all, he reveals his treasures to us when we conduct special excavations.
Photo: Michael LaMartin
How did the remnants of organisms of the past come to us?
Once in a river, lake or coastal strip of the sea, the remains of organisms can sometimes quickly become covered with silt, sand, clay, soaked in salts and thus "petrified" forever. In river deltas, coastal zones of seas, lakes, sometimes there are large accumulations of fossil organisms, which form huge "cemeteries". Fossils are not always fossilized.
There are remains of plants and animals (especially those that have recently lived) that have changed slightly. For example, the corpses of mammoths that lived several thousand years ago are sometimes found completely preserved in the permafrost. Usually animals and plants are rarely preserved intact. Most often, their skeletons, individual bones, teeth, shells, tree trunks, leaves or their imprints on stones remain.
Russian paleontologist Professor I.A. Efremov in recent years has developed in detail the doctrine of the burial of ancient organisms. From the remains of organisms, you can tell what kind of creatures they were, where and how they lived and why they changed. In the vicinity of Moscow, you can see limestone with numerous coral remains. What conclusions follow from this fact? It can be argued that the sea was noisy in the Moscow region, and the climate was warmer than now. This sea was shallow: after all, corals do not live at great depths. The sea was salty: there are few corals in the desalinated seas, but here they are abundant. Other conclusions can be drawn from a good study of the structure of corals. Scientists can, from the skeleton and other preserved parts of the animal (skin, muscles, some internal organs), restore not only its appearance, but also its way of life. Even in terms of the skeleton (jaw, skull, leg bones) of a vertebrate, one can make a scientifically substantiated conclusion about the structure of the animal, its way of life and its closest relatives both among fossils and among modern animals. The continuity of the development of organisms on Earth is the fundamental law of biology, discovered by Charles Darwin. The more ancient animals and plants that inhabited the Earth, the simpler they are. The closer to our time, the more complex organisms become and more and more similar to modern ones.
According to paleontology and geology, the history of the Earth and life on it is divided into five eras, each of which is characterized by certain organisms that prevailed during that era. Each era is divided into several periods, and the period, in turn, is divided into eras and centuries. Scientists have established what geological events and what changes in the development of living nature took place during a particular era, period, epoch. Science knows several ways to determine the age of ancient layers, and, consequently, the time of existence of certain fossil organisms. Scientists have established, for example, that the age of the most ancient rocks on Earth, the Archean era (from the Greek word "archaios" - ancient) is about 3.5 billion years. The duration of theological eras and periods was calculated in various ways. The era in which we live is the youngest. It is called the Cenozoic era of new life. It was preceded by the Mesozoic - the era of middle life. The next in seniority is the Paleozoic era of ancient life. Even earlier there were the Proterozoic and Archean eras. Calculating the age of the distant past is very important for understanding the history of our planet, the development of life on it, the history of human society, as well as for solving practical problems, including scientifically based searches for minerals. It takes seconds to see how the minute hand has moved; two to three days to see how much the grass has grown; three to four years to notice a young man becoming an adult. It takes millennia to notice some changes in the outlines of continents and oceans. The time of human life is an imperceptible moment on the grandiose hours of the history of the Earth, so people have long thought that the outlines of the oceans and land are constant, and the animals and plants that surround a person do not change. Knowledge of the history and laws of the development of life on Earth is necessary for everyone; it serves as the foundation of a scientific understanding of the world and opens the way for conquering the forces of nature.
Seas and oceans - the birthplace of life on earth
From the beginning of the Archean era we are separated by 3.5 billion years. No remains of organisms have been found in the layers of sedimentary rocks that have accumulated during this era. But it is indisputable that living beings already existed then: in the sediments of the Archean era, accumulations of limestone and a mineral similar to anthracite were found, which could have formed only as a result of the activities of living beings. In addition, in the layers of the next, Proterozoic era, remains of algae and various marine invertebrates were found. There is no doubt that these plants and animals descended from simpler representatives of wildlife that lived on Earth already in the Archean era. What could be these ancient inhabitants of the Earth, the remains of which have not survived to this day?
Academician A.I. Oparin and other scientists believe that the first living things on Earth were drops, lumps of living matter that did not have a cellular structure. They arose from inanimate nature as a result of a long and complex development process. The first organisms were neither plants nor animals. Their bodies were soft, fragile, quickly decaying after death. The rocks in which the first creatures could have been petrified by being subjected to tremendous pressure and heat have changed a lot. For this reason, no traces or remnants of ancient organisms could survive to this day. Millions of years passed. The structure of the first precellular creatures became more and more complicated and improved. Organisms have adapted to constantly changing conditions of existence. At one of the stages of development, living things acquired a cellular structure. Such primitive tiny organisms - microbes - are now widespread on Earth. In the process of development, some ancient unicellular organisms developed the ability to absorb light energy, due to which they decompose carbon dioxide and use the released carbon to build their bodies.
This is how the simplest plants arose - blue-green algae, the remains of which were found in the oldest sedimentary deposits. The warm waters of the lagoons were inhabited by countless single-celled organisms - flagellates. They combined plant and animal nutrition. Their representative, the green euglena, is probably known to you. From flagellates, various types of real plant organisms arose: multicellular algae - red, brown and green, as well as fungi. Other primitive creatures over time acquired the ability to feed on organic matter created by plants, and gave rise to the animal kingdom. The ancestors of all animals are considered to be unicellular, similar to amoebas. They gave rise to foraminifers, radiolarians with siliceous openwork skeletons of microscopic sizes and ciliates. The origin of multicellular organisms is still a mystery. They could come from colonies of unicellular animals, due to the fact that their cells began to perform various functions: nutrition, movement, reproduction, protective (cover), excretory, etc. But no transitional stages were found. The emergence of multicellular organisms is an exceptional stage in the history of the development of living beings. It was only thanks to him that further progress became possible: the emergence of large and complex organisms. The change and development of ancient multicellular organisms took place in different ways depending on the environmental conditions: some became inactive, settled on the bottom and attached to it, others retained and improved the ability to move and led a mobile lifestyle. The first, most simply arranged multicellular organisms were sponges, archaeocyates (similar to sponges, but more complex organisms), coelenterates. Among the groups of coelenterates - ctenophores, similar to elongated jellyfish, there were the future ancestors of an extensive group of worms. Some part of the ctenophores gradually switched from swimming to crawling along the bottom. This change in lifestyle was reflected in their structure: the body flattened, there were differences between the dorsal and abdominal sides, the head section began to detach, the locomotor apparatus developed in the form of a musculocutaneous sac, the respiratory organs were formed, the motor, excretory and circulatory systems were formed. It is interesting that in most animals and even in humans, the blood has a salinity similar in composition to the salinity of sea water. After all, the seas and oceans were the birthplace of ancient animals.
Questions to consider:
1. Theories of the origin of life on Earth.
2. Proof of ancient life.
3. Geochronological table. Variety of life in every period
1. Theories of the origin of life.
There are several hypotheses for the origin of life on Earth.
1. God created life.
2. Life is brought from outer space.
3. Life has arisen by itself as a result of chemical reactions.
According to scientists, life originated 4 billion years ago. It originated as a result of spontaneous chemical reactions that led to the formation of organic acids.
In the first half of the 20th century, American chemist Stanley Miller conducted an experiment in which he tried to recreate the conditions of life on Earth that prevailed about 4 billion years ago. An electric current was passed through an aqueous solution containing chemical elements. at that time, the Earth's atmosphere was rife with lightning. As a result of this experiment, simple carbon compounds appeared. Later, complex carbon compounds were also found in meteorites. Therefore, there is an assumption that the origin of life was facilitated by chemicals carried from space. However, most scientists adhere to the third hypothesis - life arose independently and developed gradually as carbon compounds became more diverse and complex.
According to scientists, the origin of life took place in the sea. on land, there was destructive radiation and strong temperature drops. Mineral substances dissolve well in water and chemical reactions proceed without difficulty.
Finally, a grandiose event took place in the history of the Earth - a fairly stable complex molecule, capable of self-reproduction, arose. For millions of years, the so-called "primary broth" appeared - a liquid medium teeming with microorganisms. Such reasoning is not groundless speculation of scientists. But there is compelling evidence that the earliest primitive forms of life quickly spread throughout the seas of the planet. What the petrified testifystromatolites age 3.5 billion years.
The drift of life from space is not excluded. After all, finding bacteria on the skins of spaceships. Found the remains of bacteria in meteorites.
2. Evidence of ancient life.
The science that studies a variety of data about the life of past years is calledpaleontology.
Evidence for the existence of ancient living organisms are:
1. Traces legs or crawls, preserved on soft silt, solidifying magma, which subsequently solidifies. Footprints can indicate the size of the animal, the way it moves.
From the bones, you can get an idea of \u200b\u200bthe position of the body, size, way of feeding and movement. Based on the scars on the bones, showing the place of muscle attachment, a conclusion is made about the location and size of the muscles, therefore, the shape of the animal's body is created. Color, length of coat and size of scales - these signs are speculative.
3. Prints leaves, animals.
4. Frozen organisms in soil or ice. In Siberia, mammoths have been found that have survived for 25 thousand years.
5. Contained in amber plants, insects, spiders. Amber is a fossil resin from conifers.
Fossil organisms are found buried in ash, swamps, quicksand, tar pit (Los Angeles), frozen patches of soil and ice.
3. Geochronological table. The variety of life in every period.
The age of fossil remains is determined by radiocarbon, which can be used to determine the age of any organic matter by the period of its decay.
To streamline the long history of the Earth, scientists divide it into different periods of time. The longest are eras. Eras are divided into periods, and periods into eras.
1. ARCHEAN ERA
It began about 3.8 billion years ago, lasted 1.3 billion years. At the beginning of Archea, life arose on the planet: its chemical traces were found in rocks with an age of 3.7 billion years. The microorganisms that left them were unicellular. These primitive creatures were similar to modern bacteria and fed on organic compounds dissolved in water.
2. PROTEROSOIC ERA
Prevendian period 2500 - 650 million years ago
Translated from Greek. "Proterozoic" - "early life".
Tiny cyanobacteria appeared on Earth - blue-green algae, which used the energy of the sun to grow. They have photosynthesis. Their descendants still exist.
Cyanobacteria lived in shallow seas. Some formed huge chunks of lime - stromatolites, fossils of which are found in ancient rocks. Modern algae still form them.
Vendian period 650-540 million years ago
The first animals appeared 1 billion years ago. Their bodies were composed of many cells. At the end of an era at the bottom of the sea livedharni, like bunches of feathers.
3. PALEOZOIC ERA
Translated from Greek. "Paleozoic" - "ancient life".
Cambian period 540-510 (505) million years ago
During this period, various multicellular animals were formed: trilobites, gastropods, brachiopods and bivalves, crustaceans, arachnids, sponges, corals, echinoderms. Many have acquired shells and shells. Many species gave rise to the modern chord.
Shoulders - sedentary animals with a bivalve shell and feeding on plankton.
Trilobites - primitive arthropods (ancestor of crayfish, spiders and insects) with an elongated flat body covered with a hard shell in the form of plates. Every segment of the body, except the last, carried limbs. Sizes 1 to 5- 7 cm in length. There were types up to 60- 75 cm.
Plants were dominated by unicellular and multicellular algae, which produced oxygen intensively.
Ordovician period 505-438 million years
It is characterized by the appearance of nautiloid molluscs - relatives of octopuses and squids. Of the arthropods were trilobites, horseshoe crabs. Lived differently; molluscs, corals. The first fish appeared. They did not yet have fins and jaws, but they had a bone shell on their heads, apparently serving as protection from predators. These first fish, known ascorymbose,were poor swimmers, and the lack of jaws forced them to eat as follows: they sucked in the silt, and then filtered it through peculiar cracks, and thus small invertebrates remained in their mouths, which served them as food. In our time, such creatures would certainly seem primitive and awkward, but then they were the most developed animals on Earth. First, they had a spine that, when combined with other bones, formed a solid skeleton. Secondly, they reached a much larger size than other animals. And thirdly, they already had eyes, a mouth, and even a small amount of brain.
Silurian period 438-408 million years ago
During this period, the continents rose higher and the climate became cool. Photosynthesis played a huge role in the further evolution of life on Earth. In the process of photosynthesis, oxygen is released, which in the upper layers turns into ozone, which can absorb the deadly ultraviolet rays. The layer of ozone thickened over time and finally blocked access to excess ultraviolet rays. This made it possible for living organisms to rise from the bottom of the ocean to the surface, and then come out onto land.
Plants were the first to appear on land. This became possible about four hundred and ten million years ago, when the ozone layer became thick enough to completely block the access of deadly ultraviolet rays. Plants mastered the land slowly - until the next period they adapted.
The fact is that in water they were able to absorb water and food across their entire surface, and on land they could only do this by their widely branched and deeply buried roots. To live on land, plants needed a water transport system that ran from root to top, a hard skin to reduce moisture loss, and a solid foundation to keep the stem or trunk upright.
The first plant to meet all of these requirements was the cuxonia, which grew in Wales nearly four hundred million years ago. Following it, other types of land plants appeared - mosses, lyes, ferns, varieties of conifers. During the Carboniferous period, which began 345 million years ago, they thrived, forming huge swampy forests. Some mosses in these forests were about a ten-story building, the ferns reached a height of forty-five meters, and how huge the trees were, it's hard to even imagine.
Following the plants, the simplest animals began to adapt to life on land. Adapted to breathe air.
Probably the first of them were the most ancient arthropods, which, in the process of evolution, were able to acquire for themselves the simplest apparatus for breathing air. From these ancient arthropods, mites, centipedes, scorpions and other insects later evolved. All of them ate plants and for many millions of years were the only inhabitants of the land. The most curious of the ancient insects was the giant dragonfly, whose wingspan exceeded seventy centimeters.
Algae and fish continued to dominate the seas. Giant crustaceans appeared before 3m in length. Some fish have developed jaws. This allowed their owners to eat not only the simplest organisms, but also larger animals. Having overtaken the prey, they tore it apart with the help of their jaws, and then swallowed it.
The earliest jawfish were Acanthodians. Then they were supplanted by the plasoderm, which grew to very large sizes. The largest of them, the dunkleosteus, was ten meters long. Instead of teeth, there were bone spines on his jaws, but this did not prevent him from killing and n; obese everything that caught his eye.
Devonian period 408-360 (362) million years ago
The heyday of fish. Panzer fish evolved and three types appeared: lungfinned, cross-finned and ray-finned (ancestors of modern fish).
The largest marine animals appeared - yes (u) nkleosteus 4 m length, cutting its prey in half. Later sharks appeared and migrated to the ocean.
The first amphibians appeared, descended from fish that came out on land. The reason for the release of fish was the drying up of small reservoirs.
In order not to die, the fish were forced to crawl over land to another body of water. They did it awkwardly at first, and very few probably achieved their goals. But over time, growths formed on the fins of these fish, which could be supported, and in addition to the gills, tiny lungs appeared, allowing them to absorb oxygen from the air. In the process of evolution, the fins finally turned into limbs, and the lungs expanded so much that they allowed to breathe air constantly. This happened about 350 million years ago.
One of the first amphibians was the ichthyostega. She already
there were well-formed lungs and limbs resembling the paws of modern amphibians and reptiles.
The ability to move both on land and on water made it possible for amphibians to maneuver in case of danger and feed on both underwater organisms and those that lived on land. Subsequently, reptiles evolved from amphibians, and from them, in turn, birds and mammals.
Among the amphibians was the Stegocephalus, which has real limbs.
Carboniferous period 360-286 million years ago
The continents are covered with low-lying swamps and fern forests. Giant forests of warm and moist Carboniferous were teeming with giant insects, large amphibians. The wingspan of insects reached 75 cm long.
During this period, the first reptiles appear - Dimetrodon, Edaphosaurus. A "sail" stretches along their backs, allowing them to regulate their body temperature.
Perm 286-245 (250) million years ago
The climate gets colder, it becomes more arid. Continents rise, lakes and seas dry up. The number of ferns, horsetails and lyres is decreasing. Mountain building takes place. The glaciation of the southern hemisphere is coming.
At the end of the Permian period, animals appear, similar to reptiles, which gave rise to mammals. During this period, a mass extinction of species occurs on the earth due to climate change.
4. MESOZOIC ERA
"Mesozoic" - "average life". They call it the era of reptiles.
Triassic period 245-208 million years
After disappearingspecies on Pangea (one continent) a warmer and more humid climate has been established. Treelike fern forests covered the spaces.
Dinosaurs appear. The first flying reptiles appear. The presence of the oldest oviparous mammals (like the platypus and echidna)
Jurassic period 208-144 million years
Cretaceous period 144-66 million years
Textbook for grades 10-11
Chapter XIII. Development of life on Earth
The history of living organisms on Earth is studied by the remnants, imprints and other traces of their life preserved in sedimentary rocks. This is the science of paleontology. For ease of study and description, the entire history of the Earth is divided into periods of time that have different durations and differ from each other in climate, intensity of geological processes, the appearance of some and the disappearance of other groups of organisms, etc. In the geological record, these time intervals correspond to different layers of sedimentary rocks with included fossil remains. The deeper the sedimentary layer is located (unless, of course, the layers are inverted as a result of tectonic activity), the older the fossils there are. This determination of the age of the finds is relative. In addition, it must be remembered that the emergence of one or another group of organisms occurs before it appears in the geological record. The group must become large enough so that after hundreds of millions of years we can find its representatives during excavations.
Figure: 71. The history of the development of life on Earth and the formation of the modern atmosphere
The names of these periods of time are of Greek origin. The largest such subdivisions are zones, there are two of them - cryptose (latent life) and phanerozoic (explicit life). Zones are divided into eras (Fig. 71). There are two eras in Cryptozoic - Archean (the oldest) and Proterozoic (primary life). Phanerozoic includes three eras - Paleozoic (ancient life), Mesozoic (middle life) and Cenozoic (new life). In turn, the eras are divided into periods, the periods are sometimes divided into smaller parts. In order to find out which real time intervals correspond to eras and periods, the content of isotopes of various chemical elements in rocks and the remains of organisms is determined. Since the rate of decay of isotopes is strictly constant and well known value, it is possible to determine the absolute age of the found fossils. The further from us this or that period of time is, the less accurately its age is determined.
§ 55. Development of life in cryptozoic
According to scientists, the planet Earth was formed 4.5-7 billion years ago. About 4 billion years ago, the earth's crust began to cool and solidified, conditions arose on Earth that allowed living organisms to develop. These first organisms were unicellular, did not have hard shells, so it is very difficult to find traces of their vital activity. It is not surprising that scientists have long believed that the Earth was a lifeless desert for a significant part of its existence. Although cryptose accounts for about 7/8 of the entire history of the Earth, an intensive study of this zone began only in the middle of the 20th century. The use of modern research methods, such as electron microscopy, computed tomography, molecular biology methods, has made it possible to establish that life on Earth is much older than previously thought. Currently, science does not know of such sedimentary rocks in which there would be no traces of vital activity. In the oldest known sedimentary rocks on Earth, which are 3.8 billion years old, substances were found that were apparently part of living organisms.
Archaea. Archaea is the oldest era, it began over 3.5 billion years ago and lasted for about 1 billion years. At that time, there were already quite numerous cyanobacteria on Earth, the fossilized waste products of which - stromatolites - were found in significant quantities. The fossilized cyanobacteria themselves were found by Australian and American researchers. Thus, a kind of "prokaryotic biosphere" already existed in the Archean. Cyanobacteria usually need oxygen to function. There was no oxygen in the atmosphere yet, but they apparently had enough oxygen, which was released during chemical reactions that took place in the earth's crust. Obviously, the biosphere, consisting of anaerobic prokaryotes, existed even earlier. The most important event of the Archean was the emergence of photosynthesis. We do not know which organisms were the first photosynthetics. The earliest evidence for the existence of photosynthesis is carbon-containing minerals with an isotope ratio that is characteristic of carbon that has passed through the process of photosynthesis. These minerals are over 3 billion years old. The emergence of photosynthesis was of great importance for the further development of life on Earth. The biosphere received an inexhaustible source of energy, and oxygen began to accumulate in the atmosphere (see Fig. 71). The oxygen content in the atmosphere remained low for a long time, but the prerequisites for the rapid development of aerobic organisms appeared in the future.
Proterozoic. The Proterozoic era is the longest in the history of the Earth. It lasted for about 2 billion years. About 600 million years after the beginning of the Proterozoic, about 2 billion years ago, the oxygen content reached the so-called "Pasteur point" - about 1% of its content in the atmosphere today. Scientists believe that this concentration of oxygen is sufficient to ensure the sustainable functioning of single-celled aerobic organisms. A slow but constant increase in the oxygen content in the atmosphere contributed to the improvement of cellular respiration, the occurrence of oxidative phosphorylation. Oxidative phosphorylation, being a significantly more efficient way of utilizing carbohydrate energy than anaerobic glycolysis, in turn led to the prosperity of aerobic organisms. The accumulation of oxygen in the atmosphere led to the formation of an ozone screen in the stratosphere, which made life on land fundamentally possible, protecting it from the deadly hard ultraviolet radiation. Prokaryotes - bacteria and unicellular algae - apparently lived on land, in films of water between mineral particles in zones of partial flooding near water bodies. The result of their vital activity was the formation of soil.
Figure: 72. Flora and fauna of the Late Proterozoic.
1 - multicellular alga; 2 - sponge; 3 - jellyfish; 4 - crawling annelid worm; 5 - sessile annelid worm; 6 - eight-pointed coral; 7 - primitive arthropods of unclear systematic position
The emergence of eukaryotes was an equally important event. It is unknown when it happened, as it is very difficult to fix it. Research at the molecular level has led some scientists to speculate that eukaryotes may be as ancient as prokaryotes. In the geological chronicle, signs of eukaryotic activity appeared approximately 1.8-2 billion years ago. The first eukaryotes were unicellular organisms. Apparently, they have already formed such fundamental signs of eukaryotes as mitosis and the presence of membrane organelles. One of the most important aromorphoses, sexual reproduction, is attributed to the time of 1.5-2 billion years ago.
The most important stage in the development of life was the emergence of multicellularity. This event gave a powerful impetus to an increase in the diversity of living organisms and their evolution. Multicellularity makes possible the specialization of cells within the same organism, the emergence of tissues and organs, including the sense organs, active foraging, movement. These advantages contributed to the wide dispersal of organisms, the development of all possible ecological niches and, ultimately, the formation of the modern biosphere, which replaced the "prokaryotic" one. The first multicellular organisms appeared in the Proterozoic at least 1.5 billion years ago. However, some scientists believe that this happened much earlier - about 2 billion years ago. These were apparently algae.
An outbreak of animal diversity. The end of the Proterozoic, about 680 million years ago, was marked by a powerful outbreak of the diversity of multicellular organisms and the appearance of animals (Fig. 72). Before this period, finds of multicellular organisms are rare and are represented by plants and, possibly, fungi. The fauna that arose at the end of the Proterozoic was named Ediacaran in the area in South Australia, where in the middle of the XX century. the first animal prints were found in layers 650-700 million years old. Subsequently, similar finds were made on other continents. These findings served as the reason for the isolation of a special period in the Proterozoic, which was called the Vendian (after the name of one of the Slavic tribes that lived on the shores of the White Sea, where many fossil remains of representatives of this fauna were found). Wend lasted about 110 million years. During this short time in comparison with the previous epochs, a large number of species of multicellular animals, belonging to the types of coelenterates, worms, and arthropods, arose and achieved significant diversity. Some of these animals were up to 1 m in length, apparently, they were gelatinous, like jellyfish. A distinctive feature of the animals of the Vendo-Ediacaran fauna is the absence of any skeleton. Probably, then there were still no predators from which it was necessary to defend themselves.
What is the reason for such an outbreak of diversity? Scientists suggest that at the end of the Proterozoic, our planet was undergoing significant upheavals. Hydrothermal activity was very high, mountain building was going on, glaciations were replaced by climate warming. The oxygen content has increased in the atmosphere. An increase in the oxygen content up to 5-6% of the current level, apparently, was necessary for the successful existence of rather large multicellular animals. These changes in the habitat, obviously, led to the emergence of new types and their rapid development. It ended with cryptosis, the eon of "hidden life" covering more than 85% of the entire lifetime of life on Earth; a new stage began - phanerozoic.
- How is the relative and absolute age of paleontological finds determined?
- What are the main aromorphoses that can be distinguished in the evolution of unicellular organisms?
- How did the vital activity of living organisms affect the change in the geological shells of the Earth?
- 4. How can you explain the emergence of a wide variety of multicellular animals at the end of the Proterozoic?
Each of us is sometimes worried about such questions to which it is 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.
Katarchei
Katarchei - when the earth was lifeless. Volcanic eruptions were everywhere, ultraviolet radiation and oxygen was absent. 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 has existed for as long as life on it.
The era of Katarchea lasted from 5 to 3 billion years ago. Studies have shown that during this period the planet did not have a core and earth's crust. An interesting fact is that at that time the day lasted only 6 hours.
Archaea
The next era after the Katarchean is the Archaean (3.5-2.6 billion years BC). It is divided into four periods:
- neoarchean;
- mesoarchean;
- paleoarchean;
- eoarcheus.
It was during the Archean that the first protozoa were born. Few people know, but the sulfur and iron deposits 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. During 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 stages:
- mesoproterozoic;
- neoproterozoic.
This period is characterized by the appearance of the ozone layer. It was also at this time, according to historians, that the volume of the world's oceans was fully formed. The Paleoproterozoic era included the Siderian period. It was in it that the formation of anaerobic algae took place.
Scientists note that it was in the Proterozoic that global glaciation took place. It lasted for 300 million years. A similar situation is characteristic of the Ice Age, which was much later. During the Proterozoic, sponges and mushrooms appeared among them. It was during this period that ore and gold deposits 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 are not the ancestors of modern animals and plants.
Paleozoic
Scientists have been studying the geological eras of the Earth and the development of the organic world for a long time. 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 Earth development that terrestrial plants began to form. It is worth noting that during the Paleozoic period, animals came to land.
The era of the Paleozoic was explored 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 conducted research to find out Eras, as we said earlier, could last long enough. It is for this reason that during one chronology on a certain site of the Earth at different times there can be an absolutely opposite climate. So it was in the Paleozoic. At the beginning of the era, the climate was milder and warmer. There was no zonality as such. The oxygen percentage increased steadily. The water temperature ranged from 20 degrees Celsius. Over time, zoning 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 were formed. This stage has become one of the most important for the development of life on Earth. The era of the Paleozoic gave impetus to the enrichment of the planet with flora and fauna.
Plant and animal kingdom of the Paleozoic era
At the beginning of the Paleozoic period, life was concentrated in water bodies. In the middle of the era, when the amount of oxygen reached a high level, land development 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 who mastered the land were psilophytes. It is worth noting that they had no roots. The process of the formation of gymnosperms is also attributed to the Paleozoic era. Treelike plants also appeared. In connection with the appearance of flora on the 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. Eras and living organisms have been constantly changing. The first representatives of the fauna are invertebrates and spiders. Over time, insects with wings, ticks, mollusks, dinosaurs, and reptiles appeared. In the late Paleozoic, significant climatic changes took place. 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.
Mineral resources of the Paleozoic era
The formation of many minerals is associated with the Paleozoic period. 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 make up 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 for 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 began. The division of Eurasia and America took place. It is believed that it was in the warmest climate. 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 forming. It is in the Mesozoic period that fauna flourishes. Reptiles become the most developed. 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-water plants is decreasing. Invertebrates are also gradually dying 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
The Cenozoic is exactly the era in which we live today. It began about 66 million years ago. At the beginning of the era, continental division 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 sea animals. Mammals and angiosperms predominate. It was at this time that all living organisms evolve strongly and differ in a large number of subspecies. Cereals appear. The most important transformation is the appearance of Homo sapiens.
Human evolution. Initial stages of development
The exact age of the planet is impossible to determine. Scientists have been debating this topic for a long time. Some believe that the age of the Earth is 6000 thousand years, others that more than 6 million. I guess we will never know the truth. The most important achievement of the Cenozoic era is the emergence of Homo sapiens. Let's take a closer look at exactly how this happened.
There are many opinions regarding the formation of humanity. Scientists have repeatedly compared a wide variety of DNA sets. They came to the conclusion that monkeys have the most similar organism to humans. It is impossible to prove this theory completely. Some scientists argue that the human body and the pig are also quite similar.
Human evolution is visible with the naked eye. At first, biological factors were important for the population, and today - social ones. Neanderthal, Cro-Magnon, Australopithecus and others - all this through which our ancestors passed.
Parapithecus is the first stage in the development of a modern person. At this stage, our ancestors existed - monkeys, namely chimpanzees, gorillas and orangutans.
The next stage of development was the Australopithecus. The first remains found were in Africa. According to preliminary data, their age is about 3 million years. Scientists investigated the find and came to the conclusion that Australopithecines are quite similar to modern humans. The growth of the representatives was quite small, about 130 centimeters. The mass of the Australopithecus was 25-40 kilograms. Most likely, they did not use the tools, since they have not been found.
A skilled man was similar to Australopithecus, but, unlike them, he used a primitive tool. His hands and phalanges were more developed. It is believed that it is a skilled person who is our direct ancestor.
Pithecanthropus
The next stage of evolution was Pithecanthropus - Homo erectus. His first remains were found on the island of Java. According to scientists, Pithecanthropus 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 Pithecanthropus inhabited all continents. The body of a bipedal person 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 a bipedal person led an active lifestyle. Pithecanthropus hunted and made simple tools. They lived in groups. So it was easier for Pithecanthropus to hunt and defend themselves from the enemy. Findings in China suggest that they also knew how to use fire. Pithecanthropus developed abstract thinking and speech.
Neanderthal
The Neanderthals lived about 350 thousand years ago. About 100 remains of their vital activity were found. The skull of the Neanderthals 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 an ice age. It was thanks to this that the Neanderthals learned to sew clothes from leather and keep the fire constantly. There is an opinion that the 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 tools and elements for dwellings. However, it should be noted that they were quite primitive.
Cro-Magnon
Cro-Magnons were tall, which was about 180 centimeters. They had all the characteristics of modern man. Over the past 40 thousand years, their appearance has not changed at all. After analyzing the human remains, scientists concluded that the average age of Cro-Magnons was about 30-50 years. It is worth noting that they created more complex types of weapons. Among them are knives and harpoons. 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.
Homo sapiens built his dwelling from stone or dug it out in the ground. For more convenience, the nomadic population created temporary huts. 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, rock carvings made by Cro-Magnons have been found. It should be emphasized that Cro-Magnons always left their drawings in hard-to-reach places. Perhaps they performed some kind of magical role.
The Cro-Magnon technique of drawing drawings was varied. Some clearly traced the images, while others scribbled them out. The Cro-Magnons used colored paints. Mostly red, yellow, brown and black. Over time, they even began to grind out human figures. You can easily find all the found exhibits in almost any archaeological museum. Scientists note that Cro-Magnons were quite developed and educated. They loved to wear jewelry made from the bones of animals they killed.
There is a rather interesting opinion. It used to be that the Cro-Magnons drove out the Neanderthals in an unequal struggle. Scientists today assume 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.
Let's sum up
The geological history of the Earth began many millions of years ago. Each era has contributed to our modern life. We often don’t think about how our planet developed. Studying the information about how our Earth was formed, it is impossible to stop. The history of the evolution of the planet is capable of captivating everyone. We strongly recommend taking care of our Earth, at least so that after millions of years the history of our existence will have someone to study.
The history of the development of life is studied according to the data geologyand paleontology, since many fossil remains produced by living organisms have been preserved in the structure of the earth's crust. In place of the former seas, sedimentary rocks have formed, containing huge layers of chalk, sandstone and other minerals, representing the bottom sediments of calcareous shells and silicon skeletons of ancient organisms. There are also reliable methods for determining the age of terrestrial rocks containing organic matter. Usually, a radioisotope method is used, based on measuring the content of radioactive isotopes in the composition of uranium, carbon, etc., which changes regularly over time.
Immediately, we note that the development of life forms on Earth proceeded in parallel with the geological restructuring of the structure and relief of the earth's crust, with a change in the boundaries of the continents and the world's oceans, the composition of the atmosphere, the temperature of the earth's surface and other geological factors. These changes determined, to a decisive extent, the direction and dynamics of biological evolution.
The first traces of life on Earth date back to about 3.6–3.8 billion years. Thus, life arose soon after the formation of the earth's crust. In accordance with the most significant events of geobiological evolution in the history of the Earth, large time intervals are distinguished - eras, within them - periods, within periods - epochs, etc. For greater clarity, we will depict the calendar of life in the form of a conditional annual cycle, in which one month corresponds to 300 million years of real time (Fig. 6.2). Then the entire period of development of life on Earth will be just one conditional year of our calendar - from “January 1” (3600 million years ago), when the first protocells were formed, to “December 31” (zero years), when we live with you ... As you can see, it is customary to count geological time in reverse order.
(1) Archaea
Archean era(the era of the most ancient life) - from 3600 to 2600 million years ago, the length of 1 billion years - about a quarter of the entire history of life (on our conventional calendar these are “January”, “February”, “March” and several days of “April”).
Primitive life existed in the waters of the world's oceans in the form of primitive protocells. There was still no oxygen in the Earth's atmosphere, but there were free organic substances in the water, so the first bacteri-like organisms ate heterotrophically: they absorbed ready-made organic matter and received energy through fermentation. In hot springs rich in hydrogen sulfide and other gases, at temperatures up to 120 ° C, autotrophic chemosynthetic bacteria or their new forms, archaea, could live. As the primary reserves of organic matter were depleted, autotrophic photosynthetic cells arose. In the coastal zones, bacteria emerged on land, and soil formation began.
With the appearance of free oxygen in the water and the atmosphere (from photosynthetic bacteria) and the accumulation of carbon dioxide, opportunities are created for the development of more productive bacteria, and behind them the first eukaryotic cells with a real nucleus and organelles. They subsequently developed various protists (unicellular protozoa) and further plants, fungi, and animals.
Thus, in the Archean era, pro- and eukaryotic cells with different types of nutrition and energy supply appeared in the oceans. Preconditions have been created for the transition to multicellular organisms.
(2) Proterozoic
Proterozoic era(the era of early life), from 2600 to 570 million years ago, is the longest era, covering about 2 billion years, that is, more than half of the entire history of life.
Figure: 6.2. Eras and periods of development of life on Earth
Intensive mountain building processes have changed the ratio of ocean and land. There is an assumption that at the beginning of the Proterozoic, the Earth underwent the first glaciation, caused by a change in the composition of the atmosphere and its transparency for solar heat. Many pioneer groups of organisms, having done their job, died out, and new ones came to replace them. But on the whole, biological transformations took place very slowly and gradually.
The first half of the Proterozoic was in full bloom and dominance of prokaryotes - bacteria and archaea. At this time, the iron bacteria of the world's oceans, precipitating generation after generation to the bottom, form huge deposits of sedimentary iron ores. The largest of them are known near Kursk and Krivoy Rog. Eukaryotes were represented mainly by algae. Multicellular organisms were few in number and very primitive.
About 1000 million years ago, as a result of the photosynthetic activity of algae, the rate of oxygen accumulation increases rapidly. This is also facilitated by the completion of the oxidation of iron in the earth's crust, which until now absorbed the bulk of oxygen. As a result, the rapid development of the simplest and multicellular animals begins. The last quarter of the Proterozoic is known as the "age of jellyfish", since these and similar coelenterates constitute the dominant and most progressive form of life at that time.
About 700 million years ago, our planet and its inhabitants are going through the second ice age, after which the progressive development of life becomes more and more dynamic. During the so-called Vendian period, several new groups of multicellular animals were laid, but life is still concentrated in the seas.
At the end of the Proterozoic, triatomic oxygen O 3 accumulates in the atmosphere. It is ozone that absorbs the ultraviolet rays of sunlight. The ozone shield reduced the mutagenicity of solar radiation. Further neoplasms were numerous and varied, but they were less and less radical - within the already formed biological kingdoms (bacteria, archaea, protists, plants, fungi, animals) and the main types.
So, during the Proterozoic era, the dominance of prokaryotes was replaced by the dominance of eukaryotes, there was a radical transition from unicellularity to multicellularity, the main types of the animal kingdom were formed. But these complex life forms existed exclusively in the seas.
The terrestrial land at this time represented one large continent; geologists gave it the name Paleopangea. In the future, global plate tectonics of the earth's crust and the corresponding drift of continents will play an important role in the evolution of terrestrial life forms. In the meantime, in the Proterozoic, the rocky surface of the coastal areas was slowly covered with soil, bacteria, lower algae, the simplest unicellular animals settled in damp lowlands, which still existed perfectly in their ecological niches. The land was still waiting for its conquerors. And on our historical calendar there was already the beginning of “November”. Before the “New Year”, before our days, there were less than “two months”, only 570 million years.
(3) Paleozoic
Palaeozoic(era of ancient life) - from 570 to 230 million years ago, the total length is 340 million years.
Another period of intense mountain building led to a change in the relief of the earth's surface. Paleopangaea split into the giant continent of the Southern Hemisphere, Gondwana, and several small continents in the Northern Hemisphere. Former land areas were under water. Some groups died out, but others adapted and mastered new habitats.
The general course of evolution, starting from the Paleozoic, is shown in Fig. 6.3. Please note that most of the evolutionary trends of organisms that originated at the end of the Proterozoic continue to coexist with newly emerging young groups, although many are reducing their volume. Nature parted with those who do not correspond to changing conditions, but retains the most successful options, selects and develops of them the most adapted and, in addition, creates new forms, among them are chordates. Higher plants appear - the conquerors of land. Their body is divided into a root and a stem, which allows it to be well fixed in the soil and extract moisture and minerals from it.
Figure: 6.3. Evolutionary development of the living world from the end of the Proterozoic to our time
The area of \u200b\u200bthe seas either increases or decreases. At the end of the Ordovician, as a result of a decrease in the level of the world ocean and a general cooling, there was a rapid and mass extinction of many groups of organisms, both in the seas and on land. In the Silurian, the continents of the Northern Hemisphere are connected to the supercontinent Laurasia, which is divided with the southern continent of Gondwana. The climate becomes drier, milder and warmer. Armored “fishes” appear in the seas, and the first articulated animals emerge on land. With a new rise in land and shrinking seas in the Devonian, the climate becomes more contrasting. Mosses, ferns, mushrooms appear on the ground, the first forests are formed, consisting of giant ferns, horsetails and lymphoids. Among animals, the first amphibians, or amphibians, appear. In the Carboniferous, swampy forests of huge (up to 40 m) tree ferns are widespread. It was these forests that left us with deposits of coal ("coal forests"). At the end of the Carboniferous there is an uplift of land and a cooling, the first reptiles appear, finally freed from water dependence. In the Permian period, the next uplift of the land led to the unification of Gondwana with Laurasia. The united continent of Pangea was formed again. As a result of the next cold snap, the polar regions of the Earth are subject to glaciation. Treelike horsetails, ploons, ferns, many ancient groups of invertebrates and vertebrates are dying out. In total, by the end of the Permian period, up to 95% of marine species and about 70% of terrestrial species became extinct. But reptiles (reptiles) and new insects are rapidly progressing: their eggs are protected from drying out by dense shells, the skin is covered with scales or chitin.
The general result of the Paleozoic is the settlement of land by plants, mushrooms and animals. At the same time, both those, and others, and the third in the process of their evolution become more complex anatomically, acquire new structural and functional adaptations for reproduction, respiration, nutrition, contributing to the development of a new habitat.
The Paleozoic ends when our calendar shows “December 7th”. Nature is “in a hurry”, the rate of evolution in groups is high, the time of transformations is being compressed, but the first reptiles are only entering the scene, and the time of birds and mammals is still far ahead.
(4) Mesozoic
Mesozoic era (era of average life) - from 230 to 67 million years ago, total length 163 million years.
The land uplift, which began in the previous period, continues. In the beginning there is a single continent called Pangea. Its total area is much larger than the land area at present. The central part of the continent is covered with deserts and mountains, the Urals, Altai and other mountain ranges have already been formed. The climate is becoming more arid. Only river valleys and coastal lowlands are inhabited by monotonous vegetation of primitive ferns, cicadas and gymnosperms.
In the Triassic, Pangea gradually splits into northern and southern continents. Among animals on land, herbivores and carnivorous reptiles, including dinosaurs, begin their "triumphant procession". Among them there are already modern species: turtles and crocodiles. Amphibians and various cephalopods still live in the seas, bony fishes of a completely modern species appear. This abundance of food attracts predatory reptiles to the sea, and their specialized branch, ichthyosaurs, is separated. From some early reptiles, small groups separated, giving rise to birds and mammals. They already have an important feature - warm-bloodedness, which will give great advantages in the further struggle for existence. But their time is still ahead, but for now, dinosaurs continue to explore terrestrial spaces.
In the Jurassic period, the first flowering plants appeared, and among the animals, giant reptiles dominate, having mastered all habitats. In warm seas, in addition to marine reptiles, bony fishes and various cephalopods, similar to modern squids and octopuses, thrive. The continents continue to split and drift with a general direction towards their present state. This creates conditions for isolation and relatively independent development of fauna and flora on different continents and island systems.
In the Cretaceous period, in addition to oviparous and marsupial mammals, placental mammals appear, carrying young for a long time in the mother's womb in contact with blood through the placenta. Insects begin to use flowers as a food source while contributing to pollination. This cooperation has benefited both insects and flowering plants. The end of the Cretaceous period was marked by a decrease in ocean level, a new general cooling and mass extinction of many groups of animals, including dinosaurs. It is believed that 10–15% of the former species diversity remains on land.
There are different versions of these dramatic events at the end of the Mesozoic. The most popular scenario is a global catastrophe caused by a giant meteorite or asteroid falling to the Earth and leading to the rapid destruction of the biosphere balance (shock wave, dusty atmosphere, powerful tsunami waves, etc.). However, everything could have been much more prosaic. The gradual restructuring of the continents and climate change could lead to the destruction of the existing food chains built on a limited circle of producers. First, some invertebrates, including large cephalopods, became extinct in the colder seas. Naturally, this led to the extinction of sea lizards, for which cephalopods were the main food. On land, there was a reduction in the growth zone and biomass of soft succulent vegetation, which led to the extinction of giant herbivores, followed by carnivorous dinosaurs. The food supply for large insects was also reduced, and flying lizards began to disappear behind them. As a result, over several million years, the main groups of dinosaurs became extinct. We must also bear in mind the fact that reptiles were cold-blooded animals and were not adapted to existence in a new, much more severe climate. Under these conditions, small reptiles - lizards, snakes - survived and developed further; and relatively large ones, such as crocodiles, turtles, and tuataras, survived only in the tropics, where the necessary food supply and a mild climate remained.
Thus, the Mesozoic era is rightfully called the era of reptiles. For 160 million years, they have experienced their heyday, the broadest divergence in all habitats and died out in the fight against the inevitable element. Against the background of these events, warm-blooded organisms - mammals and birds - have gained tremendous advantages, which have moved on to the development of liberated ecological niches.But this was already a new era. There were “7 days” left before the “New Year”.
(5) Cenozoic
Cenozoic era (era of new life) - from 67 million years ago to the present. This is the era of flowering plants, insects, birds and mammals. In this era, a man appeared.
At the beginning of the Cenozoic, the location of the continents is already close to the present, but there are wide bridges between Asia and North America, the latter is connected through Greenland with Europe, and Europe is separated from Asia by a strait. South America was isolated for several tens of millions of years. India is also isolated, although it is moving gradually northward, towards the Asian continent. Australia, which at the beginning of the Cenozoic was associated with Antarctica and South America, about 55 million years ago, completely isolated and gradually moves north. On isolated continents, special directions and rates of evolution of flora and fauna are created. For example, in Australia, the absence of predators made it possible for the ancient marsupial and oviparous mammals to survive, long extinct on other continents. Geological restructuring has contributed to the emergence of increasing biodiversity, as it created great variations in the living conditions of plants and animals.
About 50 million years ago, a detachment of primates appeared in the class of mammals on the territory of North America and Europe, which subsequently gave rise to monkeys and humans. The first people appeared about 3 million years ago (“7 hours” before the “New Year”), apparently in the eastern Mediterranean. At the same time, the climate became more and more cool, the next (fourth, counting from the early Proterozoic) ice age began. In the northern hemisphere, there have been four periodic glaciations over the last million years (as phases of an ice age alternating with temporary warming). During this time, mammoths, many large animals, ungulates became extinct. A large role in this was played by people who were actively engaged in hunting and farming. A modern human was formed only about 100 thousand years ago (after "23 hours 45 minutes on December 31" of our conditional year of life; we exist this year only for the last quarter of an hour!).
In conclusion, we emphasize once again that driving forces biological evolution must be seen in two interconnected planes - geological and biological... Each next large-scale restructuring of the earth's surface entailed inevitable transformations in the living world. Each new cold snap led to the mass extinction of poorly adapted species. Continental drift determined the difference in the rates and directions of evolution in large isolates. On the other hand, the progressive development and reproduction of bacteria, plants, fungi and animals also affected geological evolution itself. As a result of the destruction of the mineral base of the Earth and its enrichment with metabolic products of microorganisms, the soil arose and was constantly rebuilt. The accumulation of oxygen at the end of the Proterozoic led to the formation of the ozone screen. Many waste products remained forever in the bowels of the earth, transforming them irreversibly. These are organogenic iron ores, and deposits of sulfur, chalk, coal, and much more. A living thing, generated from inanimate matter, evolves with it, in a single biogeochemical flow of matter and energy. As for the inner essence and direct factors of biological evolution, we will consider them in a special section (see 6.5).
