The sequence of the appearance of plants on the planet. The main stages of the evolution of flora and fauna

And animals and many other studies have established that the Earth was formed about 5 billion years ago.

The first living organisms appeared in water about 2.5-3 billion years ago. At that time, the water of the primary ocean contained a huge amount of various organic and mineral substances. From them, the first precellular life forms were formed - microscopically small lumps of mucus. Over the course of many millions of years, they have become more complex and improved. About 1.5-2 billion years ago they gave rise to the simplest unicellular organisms.

Living organisms used organic and mineral substances dissolved in the primary ocean as food. Gradually stocks nutrients in the primary ocean began to deplete. Between the cells began the struggle for food. Under these conditions, some cells have a green pigment - chlorophyll, and they have adapted to the use of energy. sunlight to turn water and carbon dioxide into food. So arose photosynthesis, that is, the process of formation of organic substances from inorganic substances using light energy. These living organisms were like unicellular algae.

With the advent of photosynthesis, oxygen began to accumulate in the atmosphere. The composition of the air began to gradually approach the modern one, that is, it mainly consists of nitrogen, oxygen and a small amount of carbon dioxide. This atmosphere has contributed to the development of more perfect forms life.

Ancient single-celled creatures gave rise to multicellular organisms. Multicellular organisms, like the first unicellular organisms, originated in water. Various types of algae have evolved from unicellular algae. multicellular algae.

The surface of the continents and the bottom of the ocean changed over time. New continents rose, the old ones went under water. Due to the fluctuations of the earth's crust, dry land appeared in place of the seas. The study of fossil remains shows that the flora of the Earth also gradually changed.

The transition of plants to a terrestrial way of life, apparently, was associated with the existence of land areas periodically flooded and freed from water. The receding sea water lingered in the depressions. They then dried up, then again filled with water. The drying of these areas occurred gradually. Some algae have developed adaptations for living out of water. 181 .

The climate at that time the globe was damp and warm. The transition of some plants from aquatic to terrestrial lifestyle has begun. In ancient multicellular algae, the structure gradually became more complicated, and they gave rise to the first land plants. The most ancient group of terrestrial plants known to us are psilophytes 182. They existed 420-400 million years ago, and later died out.

Psilophytes grew along the banks of water bodies and were small multicellular green plants. They did not yet have stems, leaves, roots, but were branching axes, on underground parts which developed rhizoids. Psilophytes differed from algae not only in appearance, but also in a more complex internal structure. They had developed integumentary tissue - skin - and conductive tissues - wood and bast. Psilophytes reproduced by spores.

Planet Earth was formed over 4.5 billion years ago. The first single-celled life forms appeared, possibly about 3 billion years ago. First it was bacteria. They are classified as prokaryotes because they do not have a cell nucleus. Eukaryotic (with nuclei in the cells) organisms appeared later.

Plants are eukaryotes capable of photosynthesis. In the process of evolution, photosynthesis appeared earlier than eukaryotes. At that time it existed in some bacteria. These were blue-green bacteria (cyanobacteria). Some of them have survived to this day.

According to the most common hypothesis of evolution, the plant cell was formed by entering a heterotrophic eukaryotic cell of a photosynthetic bacterium that was not digested. Further, the process of evolution led to the emergence of a single-celled eukaryotic photosynthetic organism with chloroplasts (their precursors). This is how unicellular algae appeared.

The next stage in the evolution of plants was the emergence of multicellular algae. They reached a great diversity and lived exclusively in the water.

The surface of the earth did not remain unchanged. Where the earth's crust was rising, land gradually arose. Living organisms had to adapt to new conditions. Some ancient algae were gradually able to adapt to the terrestrial way of life. In the process of evolution, their structure became more complicated, tissues appeared, primarily integumentary and conductive.

The psilophytes, which appeared about 400 million years ago, are considered the first land plants. They have not survived to this day.

Further evolution of plants, associated with the complication of their structure, was already on land.

During the time of the psilophytes, the climate was warm and humid. Psilophytes grew near water bodies. They had rhizoids (like roots), with which they were fixed in the soil and absorbed water. However, they did not have true vegetative organs (roots, stems, and leaves). The movement of water and organic substances through the plant was ensured by the emerging conductive tissue.

Later, ferns and mosses originated from psilophytes. These plants have a more complex structure, they have stems and leaves, they are better adapted to living on land. However, just like the psilophytes, they remained dependent on water. During sexual reproduction, in order for the sperm to reach the egg, they need water. Therefore, they could not "go" far from wet habitats.

In the Carboniferous period (about 300 million years ago), when the climate was humid, ferns reached their dawn, many of their woody forms grew on the planet. Later, dying off, it was they who formed deposits of coal.

When the climate on Earth began to become colder and drier, ferns began to die out en masse. But some of their species before that gave rise to the so-called seed ferns, which, in fact, were already gymnosperms. In the subsequent evolution of plants, seed ferns died out, giving rise to other gymnosperms before this. Later, more advanced gymnosperms appeared - conifers.

The reproduction of gymnosperms no longer depended on the presence liquid water. Pollination took place with the help of wind. Instead of spermatozoa (mobile forms), they formed sperm (immobile forms), which were delivered to the egg by special formations of pollen grains. In addition, gymnosperms did not form spores, but seeds containing a supply of nutrients.

The further evolution of plants was marked by the appearance of angiosperms (flowering). This happened about 130 million years ago. And about 60 million years ago they began to dominate the Earth. Compared to gymnosperms, flowering plants are better adapted to life on land. It can be said that they began to use the possibilities of the environment more. So their pollination began to occur not only with the help of wind, but also through insects. This increased the efficiency of pollination. Seeds of angiosperms are found in fruits, which provide more efficient distribution. In addition, flowering plants have a more complex tissue structure, for example, in the conducting system.

Currently, angiosperms are the most numerous group of plants in terms of the number of species.

The first plant organisms arose in the will in very distant times. The first living beings were microscopically small lumps of mucus. Much later, some of them had a green color, and these living organisms became similar to unicellular algae. Single-celled creatures gave rise to multicellular organisms, which, like single-celled ones, originated in water. A variety of multicellular algae developed from unicellular algae.

The surface of the continents and the bottom of the ocean changed over time. New continents rose, the old ones went under water. Due to the fluctuations of the earth's crust, dry land appeared in place of the seas. The study of fossil remains shows that the flora of the Earth also gradually changed.

The transition of plants to a terrestrial way of life, according to scientists, was associated with the existence of periodically flooded and freed from water areas of land. The receding water lingered in the depressions. They then dried up, then again filled with water. The drying of these areas occurred gradually. Some algae have developed adaptations for living out of water.

The climate at that time on the globe was humid and warm. The transition of some plants from aquatic to terrestrial lifestyle has begun. The structure of these plants gradually became more complicated. They gave rise to the first land plants. The most ancient group of known land plants are the psilophytes.

The development of the plant world on Earth is a long-term process, which is based on the transition of plants from an aquatic to a terrestrial way of life.

Psilophytes already existed 420-400 million years ago, and later died out. Psilophytes grew along the banks of water bodies and were small multicellular green plants. They had no roots, stems, leaves. The role of their roots was performed by rhizoids. Psilophytes, unlike algae, have a more complex internal structure - the presence of integumentary and conductive tissues. They reproduced by spores.

Bryophytes and ferns evolved from psilophytes, which already had stems, leaves and roots. The heyday of ferns was about 300 million years ago in the Carboniferous period. The climate at that time was warm and humid. At the end of the Carboniferous period, the Earth's climate became noticeably drier and colder. Tree ferns, horsetails and club mosses began to die out, but by this time primitive gymnosperms had appeared - the descendants of some ancient ferns. According to scientists, the first gymnosperms were seed ferns, which subsequently became completely extinct. Their seeds developed on the leaves: these plants did not have cones. Seed ferns were tree-like, liana-like and herbaceous plants. Gymnosperms originated from them.

Living conditions continued to change. Where the climate was more severe, ancient gymnosperms gradually died out and were replaced by more perfect plants - ancient conifers, then they were replaced by modern conifers: pine, spruce, larch, etc.

The transition of plants to land is closely connected not only with the appearance of such organs as the stem, leaf, root, but, mainly, with the appearance of seeds, in a special way reproduction of these plants. Plants propagated by seeds are better adapted to life on land than plants propagated by spores. This became especially clear when the climate became less humid.

On the growths developing from spores (in mosses, club mosses, ferns), female and male gametes (sex cells) are formed - eggs and spermatozoa. In order for fertilization to occur (after the fusion of gametes), atmospheric or ground water in which the spermatozoa move to the eggs.

Gymnosperms do not need free water for fertilization, since fertilization occurs inside the ovules. They have male gametes (spermatozoa) approaching female gametes (eggs) along the pollen tubes growing inside the ovules. Thus, fertilization in spore-bearing plants is completely dependent on the availability of water; in plants propagating by seeds, this dependence is not present.

Angiosperms - descendants of ancient gymnosperms - appeared on Earth over 130-120 million years ago. They turned out to be the most adapted to life on land, since only they have special reproductive organs - flowers, and their seeds develop inside the fruit and are well protected by the pericarp.

Thanks to this, angiosperms quickly settled throughout the Earth and occupied a wide variety of habitats. For more than 60 million years, angiosperms have dominated the Earth. On fig. 67 shows not only the sequence of appearance of certain divisions of plants, but also their quantitative composition, where angiosperms are given a significant place.

plant evolution

The first living organisms arose about 3.5 billion years ago. They, apparently, fed on products of abiogenic origin and were heterotrophs. High speed reproduction led: to the emergence of competition for food, and consequently, to divergence. The advantage was given to organisms capable of autotrophic nutrition - first to chemosynthesis, and then to photosynthesis. About 1 billion years ago, eukaryotes divided into several branches, from some of which multicellular photosynthetic organisms (green, brown and red algae), as well as fungi, arose.

The main conditions and stages of plant evolution:

• in the Proterozoic era, unicellular aerobic organisms (cyanobacteria and green algae) were widespread;
• formation of soil substrate on land at the end of the Silurian;
• the emergence of multicellularity, which makes possible the specialization of cells within one organism;
• development of land by psilophytes;
• from psilophytes in the Devonian period, a whole group of terrestrial plants arose - mosses, club mosses, horsetails, ferns that reproduce by spores;
• gymnosperms originated from seed ferns in the Devonian. The structures necessary for seed reproduction (for example, the pollen tube) that arose, freed the sexual process in plants from dependence on aquatic environment. Evolution followed the path of reduction of the haploid gametophyte and the predominance of the diploid sporophyte;
• the Carboniferous period of the Paleozoic era is distinguished by a large variety of terrestrial vegetation. Arborescent ferns spread, forming coal forests;
• in the Permian period, the ancient gymnosperms became the dominant group of plants. In connection with the appearance of an arid climate, giant ferns and tree clubs are disappearing;
• in the Cretaceous period, the flowering of angiosperms begins, continuing to this day.

The main features of the evolution of the plant world:

1. transition to the predominance of the diploid generation over the haploid one;
2. development of female growth on the mother plant;
3. the transition from spermatozoa to the injection of the male nucleus through the pollen tube;
4. dismemberment of the body of plants into organs, the development of a conducting vascular system, supporting and protective tissues;
5. improvement of organs of reproduction and cross-pollination in flowering plants in connection with the evolution of insects;
6. seed development to protect the embryo from adverse environmental influences;
7. the emergence of various ways of dispersal of seeds and fruits.

Animal evolution

The most ancient traces of animals belong to the Precambrian (over 800 million years). It is assumed that they originated either from a common stem of eukaryotes or from unicellular algae, which is confirmed by the existence of Euglena green and Volvox, capable of both autotrophic and heterotrophic nutrition.

In the Cambrian and Ordovician periods, sponges, coelenterates, worms, echinoderms, trilobites predominate, and mollusks appear.

In the Ordovician, jawless fish-like organisms appear, and in the Silurian, fish with jaws appear. Ray-finned and lobe-finned fish arose from the first jawed-stomes. Crossopterygians had in their fins supporting elements, from which the limbs of terrestrial vertebrates later developed. From this group of fish arose amphibians and then other classes of vertebrates.

The most ancient amphibians are the Ichthyostegs who lived in the Devonian. Amphibians flourished in the Carboniferous.

Reptiles, which conquered land in the Permian period, originate from amphibians, thanks to the appearance of a mechanism for sucking air into the lungs, the rejection of skin respiration, the appearance of horny scales and egg shells covering the body, protecting embryos from drying out and other environmental influences. Among the reptiles, a group of dinosaurs presumably stood out, which gave rise to birds.

The first mammals appeared in the Triassic period of the Mesozoic era. Major progressive biological features mammals - feeding the young with milk, warm-bloodedness, developed cerebral cortex.

Features of the evolution of the animal world:

1. progressive development of multicellularity and, as a result, specialization of tissues and all organ systems;
2. a free-moving way of life, which determined the development of various behavioral mechanisms, as well as the relative independence of ontogeny from fluctuations in environmental factors. The mechanisms of internal self-regulation of the organism developed and improved;
3. the emergence of a solid skeleton: external in a number of invertebrates - echinoderms, arthropods; internal in vertebrates. The advantage of the internal skeleton is that it does not limit the increase in body size.

progressive development nervous system became the basis for the emergence of the system conditioned reflexes and improving behaviour.

Cyanobacteria, because their cells do not have formed nuclei. Thus, they can be attributed to prokaryotes (pre-nuclear organisms). Among the blue-green algae were unicellular and multicellular organisms that have the ability to carry out photosynthesis. Thanks to the process of photosynthesis, oxygen began to enter the atmosphere of our planet, which is necessary for the life of aerobes.

Later in the Proterozoic era (about 2600 million years ago), red and green algae took over the Earth. Their dominance extended to the Paleozoic era (about 570 million years ago). Only in the late Paleozoic (Silurian period) was the vital activity on the planet of the most ancient higher plants - rhinophytes, or psilophytes, noted. These plants had shoots but lacked roots and leaves. Reproduction of rhinophytes occurred by spores. They lived on land or partially in water. In the existence of our planet new era began with the appearance of higher, or terrestrial plants. About 400-360 million years ago, in the Devonian period of the Paleozoic era, against the background of the predominance of rhinophytes and algae on Earth, the first ferns (ferns, horsetails, club mosses) and moss-like plants appeared. They belong to the higher spore plants. Thanks to the spread of plants on land, new land species of animals also appeared. The combined change in the course of evolution of the forms of plants and animals led to huge variety life on earth. The face of the planet has changed radically. The attached way of life of a plant on land led to the appearance of a division of the plant into root, stem and leaf, as well as to the emergence of supporting tissues and a vascular conducting system. The very first land plants were small in size. They absorbed water through rhizoids, like mosses that have survived to this day on Earth. In the cycle of their development, the haploid generation (gametophyte) predominated. Gradually, larger forms of plants appeared - ferns, which formed complex specialized organs - roots with root hairs. In the development cycle of these plants, the diploid phase comes to the fore - the sporophyte, which is directly the plant itself, while the gametophyte is a growth that looks like a nodule in horsetails and club mosses and like a small heart-shaped plate in ferns. Thus, a gradual transition was carried out from the haploid generation to a more perfect - diploid one. In the Paleozoic era, ferns were huge plants that dominated the land. However, water was necessary for their reproduction, which limited the territory of their existence to areas with high humidity.

In the Carboniferous period, which lasted from 360 to 280 million years ago, the appearance of seed ferns on our planet was proved, which later became the ancestors of all gymnosperms. At this time, rhinophytes completely disappear due to the inability to compete with more developed plants. And then the huge tree-like ferns that dominated then formed deposits of coal after dying off.

In the next Permian period of the Paleozoic era, ancient gymnosperms appeared on Earth. Tree-like ferns are gradually dying out, and they are being replaced by seed and herbaceous ferns, taking possession of the land. A feature of gymnosperms is that their reproduction is carried out by seeds that do not have protection in the form of fruit walls, since these plants do not form flowers and fruits. Sexual reproduction of these plants was carried out independently of the drip-water environment. And their appearance in the course of evolutionary metamorphoses was due to changes in humidity and temperature and a change in the Earth's relief due to the rise of the land, that is, the appearance of mountain ranges.

The Mesozoic era began about 240 million years ago. In the Triassic period of the Mesozoic, modern gymnosperms appeared, and in the Jurassic period, the first angiosperms originated. But the dominant positions on the planet were preserved by gymnosperms. This is the era of the extinction of the ancient ferns, unable to withstand natural selection. In the process of the emergence of angiosperms, a series of aromorphoses occurred. First, a flower was formed - a transformed shoot adapted for the formation of spores and gametes. Pollination, fertilization and the formation of the embryo and fruit occurred directly in the flower. Secondly, for better protection and distribution of angiosperm seeds were surrounded by the pericarp. These plants are characterized by sexual reproduction. Angiosperms include herbaceous plants, trees and shrubs. Various modifications of vegetative organs (root, stem, leaf) are noted in different types plants. Evolutionary changes in angiosperms occurred in relatively short term, therefore, they are characterized by high evolutionary plasticity. Insect pollinators have played a huge role in the course of evolutionary transformations. Angiosperms more productively develop environment and conquer new territories, thanks to their structural features and the ability to form complex multi-tiered communities.

In the Cenozoic era, which began approximately 70 million years ago, our planet began to be dominated by the currently existing angiosperms and gymnosperms, while the higher spore plants regressed.

Now more than 350 species of plants grow on Earth, among them there are flowering, bryophyte plants, ferns, algae.