home · On a note · The emergence and development of life on earth. The main stages of historical development and complexity of the plant world on earth History of plant evolution

The emergence and development of life on earth. The main stages of historical development and complexity of the plant world on earth History of plant evolution

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 developed a green color, and these living organisms began to look like unicellular algae. Single-celled creatures gave rise to multicellular organisms, which, like single-celled organisms, arose in water. From unicellular algae, various multicellular algae developed.

The surface of the continents and the ocean floor have changed over time. New continents rose and previously existing ones sank. Due to vibrations of the earth's crust, land appeared in place of the seas. The study of fossil remains shows that the plant world of the Earth also gradually changed.

The transition of plants to a terrestrial lifestyle, according to scientists, was associated with the existence of land areas that were periodically flooded and cleared of water. The receding water was retained in the depressions. They either dried up or filled with water again. The drainage of these areas occurred gradually. Some algae have developed adaptations for living outside of water.

The climate at that time on the globe was humid and warm. The transition of some plants from an aquatic to a terrestrial lifestyle began. The structure of these plants gradually became more complex. They gave rise to the first land plants. The oldest group of known land plants are 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 became extinct. Psilophytes grew along the banks of reservoirs and were small multicellular green plants. They had no roots, stems, or leaves. The role of roots was played by rhizoids. Psilophytes, unlike algae, have a more complex internal structure - the presence of integumentary and conductive tissues. They reproduced by spores.

From psilophytes came bryophytes and ferns, which already had stems, leaves and roots. The heyday of ferns was about 300 million years ago during the Carboniferous period. The climate at this 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 appeared - descendants of some ancient ferns. According to scientists, the first gymnosperms were seed ferns, which later 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 advanced 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 stems, leaves, roots, but, mainly, with the appearance of seeds, a special method of reproduction of these plants. Plants that reproduced by seeds were better adapted to life on land than plants that reproduced by spores. This became especially clear when the climate became less humid.

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

Gymnosperms do not need free water for fertilization, since it occurs inside the ovules. In them, male gametes (sperm) approach female gametes (eggs) through pollen tubes growing inside the ovules. Thus, fertilization in spore plants is completely dependent on the availability of water; in plants that reproduce 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 spread throughout the Earth and occupied a wide variety of habitats. For more than 60 million years, angiosperms have dominated the Earth. In Fig. 67 shows not only the sequence of appearance of certain plant divisions, but also their quantitative composition, where angiosperms have a significant place.

Cyanobacteria, since their cells lack formed nuclei. Thus, they can be classified as prokaryotes (prenuclear organisms). Among the blue-green algae there were single- and multicellular organisms that had the ability to carry out photosynthesis. Thanks to the process of photosynthesis, oxygen, necessary for the life of aerobes, began to enter the atmosphere of our planet.

Later in the Proterozoic era (about 2600 million years ago), red and green algae took over the Earth. Their dominance extended into the Paleozoic era (approximately 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 no roots or leaves. Rhinophytes reproduced by spores. They lived on land or partially in water. In the existence of our planet, a 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 rhiniophytes and algae on Earth, the first pteridophytes (ferns, horsetails, mosses) and moss-like plants appeared. They belong to higher spore plants. Thanks to the spread of plants on land, new terrestrial animal species appeared. The combined changes in the evolution of plant and animal forms have led to the enormous diversity of life on Earth. The face of the planet has changed radically. The attached way of life of the plant on land led to the appearance of division of the plant into roots, stems and leaves, as well as to the emergence of supporting tissues and a vascular conduction system. The very first land plants were small. They absorbed water through rhizoids, like mosses that have survived to this day on Earth. The haploid generation (gametophyte) predominated in their development cycle. Gradually, larger forms of plants appeared - fern-like ones, in which complex specialized organs were formed - roots with root hairs. In the development cycle of these plants, the diploid phase comes to the fore - the sporophyte, which is the plant itself, while the gametophyte is a shoot that looks like a nodule in horsetails and mosses and like a small heart-shaped plate in ferns. This is how a gradual transition was carried out from the haploid generation to a more perfect one - the diploid one. In the Paleozoic era, ferns were huge plants that dominated the land. However, for their reproduction, water was necessary, 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, which later became the ancestors of all gymnosperms, was proven. At this time, rhinophytes completely disappear due to the inability to compete with more developed plants. And the huge tree-like ferns that were dominant at that time, after dying off, formed deposits of coal.

In the next Permian period of the Paleozoic era, ancient gymnosperms appeared on Earth. Tree ferns are gradually dying out, and they are being replaced by seed and herbaceous ferns, taking over the land. A peculiarity 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 during evolutionary metamorphoses was due to changes in humidity and temperature and changes in the Earth’s topography due to the rise of 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 arose. But the dominant position on the planet remained with gymnosperms. This is the era of extinction of ancient ferns that could not withstand natural selection. During 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 dissemination, angiosperm seeds were surrounded by a pericarp. These plants are characterized by sexual reproduction. Angiosperms include herbaceous plants, trees and shrubs. Various modifications of vegetative organs (roots, stems, leaves) are observed in different plant species. Evolutionary changes in angiosperms occurred in a relatively short period of time, so they are characterized by high evolutionary plasticity. Insect pollinators played a huge role in the course of evolutionary transformations. Angiosperms more productively develop the environment and conquer new territories, thanks to their structural features and ability to form complex multi-layered communities.

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

Now there are more than 350 species of plants growing on Earth, among them there are flowering plants, bryophytes, ferns, and algae.

As a result of prehistoric events such as the Permian and Cretaceous–Paleogene, many plant families and some ancestors of extant species became extinct before recorded history began.

The general trend of diversification includes four main groups of plants that dominate the planet from the Middle Silurian period to the present:

Zosterophyllum model

  • The first main group, representing terrestrial vegetation, included seedless vascular plants, represented by the rhinium classes ( Rhynophyta), zosterophylls ( Zosterophyllopsida).

Ferns

  • The second main group, which appeared in the late Devonian period, consisted of ferns.
  • The third group, seed plants, appeared at least 380 million years ago. It included gymnosperms ( Gymnospermae), which dominated the terrestrial flora during most of the Mesozoic era until 100 million years ago.
  • The last fourth group, the angiosperms, appeared about 130 million years ago. The fossil record also shows that this group of plants was abundant in most areas of the world between 30 million and 40 million years ago. Thus, angiosperms dominated the Earth's vegetation for almost 100 million years.

Palaeozoic

Moss-moss

The Proterozoic and Archean eons precede the appearance of terrestrial flora. Seedless, vascular, terrestrial plants appeared in the mid-Silurian period (437-407 million years) and were represented by rhinophytes and possibly lycophytes (including Lycopodium). From primitive rhyniophytes and lycophytes, land vegetation evolved rapidly during the Devonian period (407-360 million years ago).

The ancestors of true ferns may have evolved in the mid-Devonian. During the late Devonian period, horsetails and gymnosperms appeared. By the end of the period, all the main divisions of vascular plants, except angiosperms, already existed.

The development of the characteristics of vascular plants, during the Devonian, allowed an increase in the geographical diversity of the flora. One of them was the appearance of flattened leaves, which increased efficiency. Another is the emergence of secondary wood, allowing plants to greatly increase in shape and size, leading to trees and probably forests. The gradual process was the reproductive development of the seed; the earliest was found in Upper Devonian deposits.

The ancestors of conifers and cycads appeared in the Carboniferous period (360-287 million years ago). During the Early Carboniferous in high and middle latitudes, vegetation shows dominance of Lycopodium and Progymnospermophyta.

Progymnospermophyta

In the lower latitudes of North America and Europe, a wide variety of Lycopodiums and Progymnospermophyta, as well as other vegetation. There are seed ferns (including calamopityales), along with true ferns and horsetails ( Archaeocalamites).

Late Carboniferous vegetation at high latitudes was severely damaged by the onset of the Permian-Carboniferous Ice Age. In the northern mid-latitudes, the fossil record shows the dominance of horsetails and primitive seed ferns (pteridosperms) over few other plants.

In the northern low latitudes, the land masses of North America, Europe and China were covered by shallow seas or marshes and, because they were close to the equator, experienced tropical and subtropical climate conditions.

At this time, the first ones known as coal forests appeared. Vast amounts of peat were laid down as a result of favorable year-round growth conditions and the adaptation of giant Lycopodium to tropical wetland environments.

In the drier areas surrounding the lowlands, forests of horsetails, seed ferns, cordaites and other ferns existed in great abundance.

The Permian period (287-250 million years ago) indicates a significant transition of conifers, cycads, glossopteris, gigantopterids and peltasperms from poor fossil record in the Carboniferous to significant abundant vegetation. Other plants, such as tree ferns and giant lycopodiums, were present in the Permian, but not in abundance.

As a result of the Permian mass extinction, tropical swamp forests disappeared, and with them the Lycopodiums; Cordaites and Glossopteris became extinct at higher latitudes. About 96% of all plant and animal species disappeared from the face of our planet at this time.

Mesozoic era

At the beginning of the Triassic period (248-208 million years ago), the sparse fossil record indicates a decline in the Earth's flora. From the mid to late Triassic, modern families of ferns, conifers, and a now extinct group of plants, the Bennettites, inhabited most terrestrial environments. After the mass extinction, Bennettites moved into vacant ecological niches.

Late Triassic flora in equatorial latitudes includes a wide range of ferns, horsetails, cycads, bennettites, ginkgos and conifers. Plant combinations in low latitudes are similar, but not rich in species. This lack of plant variation at low and mid-latitudes reflects a global frost-free climate.

In the Jurassic period (208-144 million years ago), terrestrial vegetation similar to modern flora appeared, and modern families can be considered descendants of ferns of this geological period of time , such as Dipteridaceae, Matoniaceae, Gleicheniaceae, and Cyatheaceae.

Conifers of this age may also include modern families: podocarpaceae, araucariaceae, pine and yew. These conifers, during the Mesozoic, created significant deposits such as coal.

During the Early and Middle Jurassic period, a variety of vegetation grew in the equatorial latitudes of western North America, Europe, Central Asia and the Far East. It included: horsetails, cycads, bennettites, ginkgos, ferns and conifers.

Warm, humid conditions also existed in the northern mid-latitudes (Siberia and northwestern Canada), supporting ginkgo forests. Deserts were found in the central and eastern parts of North America and North Africa, and the presence of Bennettites, cycads, Cheirolepidiaceae and conifers indicated the adaptation of plants to arid conditions.

Southern latitudes had similar vegetation to equatorial latitudes, but due to drier conditions, conifers were abundant and ginkgos were scarce. Southern flora has spread to very high latitudes, including Antarctica, due to the lack of polar ice.

Cheirolipidae

During the Cretaceous period (144-66.4 million years ago), dry, semi-desert environments existed in South America, central and northern Africa, and central Asia. Thus, the terrestrial vegetation was dominated by Cheirolipidium conifers and Matoniaceae ferns.

The northern mid-latitudes of Europe and North America had more diverse vegetation consisting of Bennettites, cycads, ferns and conifers, while the southern mid-latitudes were dominated by Bennettites.

The Late Cretaceous saw significant changes in the Earth's vegetation, with the emergence and spread of flowering seed plants, the angiosperms. The presence of angiosperms meant the end of the typical Mesozoic flora dominated by gymnosperms and a definite decline in the Bennettites, Ginkgoaceae and Cycads.

Nothofagus or southern beech

During the Late Cretaceous, arid conditions prevailed in South America, central Africa and India, resulting in palm trees dominating tropical vegetation. The mid-southern latitudes were also influenced by deserts, and the plants that bordered these areas included: horsetails, ferns, conifers and angiosperms, particularly nothofagus (southern beech).

Sequoia Hyperion

High latitude areas were devoid of polar ice; Due to warmer climate conditions, angiosperms were able to thrive. The most diverse flora was found in North America, where evergreens, angiosperms and conifers, especially redwood and sequoia, were present.

The Cretaceous-Paleogene mass extinction (C-T extinction) occurred about 66.4 million years ago. This is an event that suddenly caused global climate change and the extinction of many animal species, especially dinosaurs.

The greatest “shock” to terrestrial vegetation occurred in the mid-latitudes of North America. Pollen and spore counts just above the K-T boundary in the fossil record show a predominance of ferns and evergreens. Subsequent plant colonization in North America shows a predominance of deciduous plants.

Cenozoic era

Increased rainfall at the beginning of the Paleogene-Neogene (66.4-1.8 million years ago) contributed to the widespread development of rain forests in the southern regions.

Notable during this period was the Arcto polar forest flora found in northwestern Canada. Mild, humid summers alternated with continuous winter darkness with temperatures ranging from 0 to 25°C.

Birch Grove

These climatic conditions supported deciduous vegetation, which included sycamore, birch, moonsperm, elm, beech, magnolia; and gymnosperms such as Taxodiaceae, Cypressaceae, Pinaceae and Ginkgoaceae. This flora spread throughout North America and Europe.

Approximately eleven million years ago, during the Miocene Epoch, marked changes in vegetation occurred with the emergence of grasses and their subsequent expansion into grassy plains and prairies. The appearance of this widespread flora contributed to the development and evolution of herbivorous mammals.

The Quaternary period (1.8 million years ago to the present) began with continental glaciation in northwestern Europe, Siberia and North America. This glaciation affected land vegetation, with flora migrating north and south in response to glacial and interglacial fluctuations. During interglacial periods, maple, birch and olive trees were common.

The final migrations of plant species at the end of the last Ice Age (about eleven thousand years ago) shaped the modern geographic distribution of land flora. Some areas, such as mountain slopes or islands, have unusual species distributions as a result of their isolation from global plant migration.

Planet Earth was formed more than 4.5 billion years ago. The first single-celled life forms appeared perhaps about 3 billion years ago. At first it was bacteria. They are classified as prokaryotes because they do not have a cell nucleus. Eukaryotic (those with nuclei in 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 the entry into a heterotrophic eukaryotic cell of a photosynthetic bacterium that was not digested. Further, the process of evolution led to the appearance of a single-celled eukaryotic photosynthetic organism with chloroplasts (their predecessors). This is how unicellular algae appeared.

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

The surface of the Earth did not remain unchanged. Where the earth's crust rose, land gradually emerged. Living organisms had to adapt to new conditions. Some ancient algae were gradually able to adapt to a terrestrial lifestyle. In the process of evolution, their structure became more complex, tissues appeared, primarily integumentary and conductive.

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

Further evolution of plants, associated with the complication of their structure, took place on land.

During the time of the psilophytes, the climate was warm and humid. Psilophytes grew near bodies of water. They had rhizoids (like roots), with which they anchored themselves 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 throughout the plant was ensured by the emerging conductive tissue.

Later, ferns and mosses evolved from psilophytes. These plants have a more complex structure, they have stems and leaves, and they are better adapted to living on land. However, just like 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.

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

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

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

The further evolution of plants was marked by the appearance of angiosperms (flowering plants). 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. We can say that they began to use the possibilities of the environment more. So their pollination began to occur not only with the help of the wind, but also with the help of insects. This increased pollination efficiency. Angiosperm seeds are found in fruits, which allow them to spread more efficiently. 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.