Origin of Life on Earth


Hypothesis AI Oparin. The most significant feature of the hypothesis Oparin - gradual complication of the chemical structure and morphological appearance of the precursors of life (probiontov) on the way to living organisms.

Large amount of data suggests that among the origin of life could be coastal seas and oceans. Here, at the junction of the sea, land and air, to create favorable conditions for the formation of complex organic compounds. For example, solutions of some organic compounds (sugars, sugar alcohols) have high stability and can exist an unlimited time. In concentrated solutions of proteins, nucleic acids can form clots such clots in aqueous gelatin solutions. These clusters are called coacervate droplets or coacervates (Fig. 66). Coacervates are able to adsorb various substances. From solution therein receives chemical compounds which are converted by reactions occurring in coacervate droplets, and released into the environment.

Coacervates - it's not sentient beings. They show a resemblance to such features of living organisms, such as growth and metabolism with the environment. Therefore, the occurrence of coacervates is considered as a stage of development prelife.

The development of life on Earth.

History of living organisms on Earth by studying preserved in sedimentary rocks residues, fingerprints and other traces of their life. This deals with the science of paleontology. For the convenience of studying and describing the whole history of the Earth is divided into time segments having different lengths and different from each other climates, the intensity of geological processes, the appearance and disappearance of some other groups of organisms, and so on. D.

The names of these times of Greek origin. The largest such units - the zone of two - kriptozoy (hidden life) and Phanerozoic (apparent life). Zones are divided into eras (Fig. 67). In kriptozoe two eras - archaea (oldest) and Proterozoic (primary life). Phanerozoic includes three eras - Paleozoic (ancient life), Mesozoic (middle life) and Cenozoic (new life). In turn, divided into periods AD periods are sometimes divided into smaller parts.

Kriptozoy.

According to scientists, the planet Earth was formed 4.5 to 7 billion. Years ago. About 4 billion. Years ago began to cool and harden the crust on Earth, conditions have allowed to develop living organisms.

Archaea.

Archaea - the most ancient era began more than 3.5 billion. Years ago and lasted for about 1 billion. Years. At this time in the world were already quite numerous cyanobacteria, petrified waste products which - stromatolites - found in significant quantities. American and Australian researchers have found themselves fossilized cyanobacteria. Thus, in the Archean already existed a kind of "prokaryotic biosphere." Cyanobacteria usually for life need oxygen. Oxygen in the atmosphere was not there, but it seems, enough oxygen, which is released during chemical reactions occurring in the earth's crust. Obviously, the biosphere, consisting sludge anaerobic prokaryotes existed before. The most important event was the emergence of the Archean photosynthesis. We do not know exactly what were the first photosynthetic organisms.

Proterozoic.

Proterozoic era - the longest in the history of the Earth. It lasted about 2 billion years.. After about 600 million. Years after the beginning of the Proterozoic, about 2 billion. Years ago, the oxygen content has reached the so-called "point Pasteur" - about 1% of its content in the atmosphere, modern to us. Scientists believe that such a concentration of oxygen is sufficient to ensure sustainable livelihoods unicellular aerobic organisms.

The outbreak of animal diversity. The end of the Proterozoic, about 680 million. Years ago, marked by a powerful flash diversity of multicellular organisms and the appearance of the animals (Fig. 68). Prior to this period, and rare findings presented multicellular plants and possibly fungi. Emerged in the late Proterozoic Ediacaran fauna was named for the area in South Australia, where in the middle of the XX century. in layers age 650-700 million. years have been found the first animal prints. Subsequently, similar findings were made on other continents. These findings caused the separation in the Proterozoic special period, known as the Vendian (under the name of one of the Slavic tribes living on the shores of the White Sea, where discovered rich fauna representatives of this location).

Paleozoic.

Palaeozoic significantly shorter earlier, it lasted about 340 million years. Land, representing at the end of the Proterozoic single supercontinent split into separate continents, grouped around the equator. This led to the creation of a large number of small coastal settlement suitable for living organisms.

By the beginning of the Paleozoic some animals formed the outer organic or mineral skeleton.

Cambrian.

Cambrian climate was temperate, continents - Plain. In the Cambrian animals and plants inhabited mainly sea. On land still live bacteria and blue-green.

Cambrian period was marked by the rapid spread of the representatives of the new types of invertebrates, many of which have lime or phosphate backbone. Scientists attribute this to the advent of predation. Among single-celled animals foraminifera were numerous - representatives of the simplest, had lime or sand glued from the sink.

Ordovician.

In the Ordovician Sea area is greatly increased. In the Ordovician seas are very diverse green, brown and red algae. Is an intensive process of reef corals. Considerable diversity observed among cephalopods and gastropods. In the Ordovician appear first chord.

Silurian.

At the end of the Silurian seen the development of unique arthropods - merostomes. By the Ordovician and Silurian is flourishing in the seas of cephalopods. There are new representatives invertebrates - echinoderms.

In the Silurian seas begins mass distribution of the first true vertebrates - armored jawless. At the end of the Silurian - Devonian beginning of intensive development of land plants. Landfall and animals. One of the first switched from an aqueous medium such as representatives of arthropods - spiders, from searing atmospheric action defended their chitinous shell.

Devon.

As a result of elevation of the land and reduce climate Devonian seas was more continental than in the Silurian. Devon appeared desert and semidesert region.

The seas inhabited by these fish, which ousted armored jawless. Among them were cartilaginous fishes (modern representatives - shark), and there were fish with bony skeleton.

In the Devonian land appear first forests of giant ferns, horsetails and club mosses. New groups of animals begin to conquer the land. Representatives of arthropods to make landfall, give rise to centipedes and insects first. At the end of the Devonian fish descendants come to the land, forming the first class of terrestrial vertebrates - amphibians (amphibians).

Carbon.

In the Carboniferous period, or carbon, there is a noticeable warming and moistening climate. In hot, tropical-type swamp forests grow huge (up to 40 m), ferns, horsetails and club mosses. In addition to these plants, breeding spores begin to spread in the Carboniferous gymnosperms, resulting in the late Devonian. Their seed was covered with a cover, protected from drying out. In humid and warm swampy forests of exceptional prosperity and diversity reached ancient amphibians - Labyrinthodontia. There are the first units of winged insects - cockroaches, body length reaches 10 cm, and dragonflies, some species of which have a wingspan of up to 75 cm.

Perm.

Further land uplift led to the development in the Permian arid climate and cooling. Wet and lush forests remain only near the equator; gradually die ferns. Are replaced by gymnosperms.

Dry climate contributed to the extinction of amphibians - Labyrinthodontia. But the great diversity of reach ancient reptiles that arose in the late Carboniferous.

Mesozoic.

Mesozoic era is rightly called reptiles. Their heyday, the widest divergence and extinction are taking place in this era.

Trias.

In the Triassic greatly reduces the area of ​​inland water bodies, developing desert landscapes. In arid climates are many extinct land organisms in which the individual stages of life are associated with water. Extinct, most amphibians, almost completely disappear tree ferns, horsetails and club mosses. Instead, they begin to dominate the terrestrial forms, in the life cycle stages which are not related to the water. Among the plants in the Triassic strong development reach gymnosperms, among animals - reptiles. Already there are the first in the Triassic representatives of warm-blooded - small primitive mammals and birds.

Jura.

In the Jurassic, there is some expansion of the area of ​​warm seas. The seas are numerous cephalopods - ammonites and belemnites.

Very diverse marine reptiles. In addition to ichthyosaurs, in the seas of the Jurassic plesiosaurs appear - animals with a broad torso, long fins and serpentine neck. Marine reptiles as if divided between food resources: plesiosaurs hunted in the shallow waters of the coastal zone, and ichthyosaurs - the high seas. In Jurassic reptiles began to explore and air. The variety of flying insects create conditions for development of carnivorous flying lizards. Small flying lizards began to eat large lizards. Flying dinosaurs existed until the end of the Cretaceous.

Mel.

Cretaceous period (or chalk) named in connection with the formation of chalk in marine sediments of the time. It emerged from the remnants of shells simplest animals - foraminifera. In this period there and very quickly spread angiosperms, gymnosperms are displaced. Widespread occurrence of the first insects and angiosperms eventually led to the connection between them. In angiosperms originated flower - reproductive organs, which attracts insects color, odor and nectar reserves. Insects feeding on nectar, pollen vectors steel. The transfer of pollen by insects compared to Anemophily leads to less waste of gametes.

At the end of the Cretaceous climate is changing in the direction of cutting-continent of continental and general cooling. The seas are becoming extinct ammonites and belemnites, and behind them and eat them marine reptiles - the plesiosaurs and ichthyosaurs. On land has been decreasing moisture-loving vegetation, is the food herbivorous dinosaurs, which led to their disappearance; and carnivorous dinosaurs became extinct. Reptiles only in the equatorial regions remained large forms - crocodiles, turtles and tuatara. Most of the surviving reptiles (lizards, snakes) were small in size.

In conditions of extreme continental climate and the general cooling exceptional benefits received warm-blooded - birds and mammals, whose flourishing refers to the following era - Cenozoic.

Cenozoic.

Cenozoic era - it is a bloom of flowering plants, insects, birds and mammals.

It began about 66 million. Years ago and continues to this day.

Paleogene.

The first period of the Cenozoic mammals replaced reptiles, taking their ecological niches on the ground, the birds began to dominate in the air. During this period, formed the majority of modern groups of mammals - insectivorous, carnivorous, pinnipeds, cetaceans, ungulates. There were first primitive primates lemurs and then the real monkey.

Neogene.

In the Neogene climate became colder and drier. Tropical forest and savanna that grew once in the temperate zone of the present-day Hungary to Mongolia, replaced steppes. This has led to a proliferation of cereals, which became a source of food for herbivorous mammals. Used this period were formed all the modern orders of mammals, the first apes.

Anthropogenic.

The last period of the Cenozoic - anthropogenic - is the geological period in which we live, and we will. Its name is due to the fact that in this period there was a person. In anthropogenic release two centuries (not centuries and centuries in the geological sense) - Pleistocene and Holocene. During the Pleistocene observed very strong climate change - there were four giant glaciers, glacier retreat is replaced.

Negative temperature in the zone of glaciation led to the fact that water vapor condensed in the form of snow, and the melting of ice and snow each year gave less water than snow falls. The accumulation of huge reserves of ice on land led to a significant decrease in the level of the oceans (60-90 m).

In the Old World (excluding Madagascar) people settled at least 500 thousand. Years ago, and possibly much earlier. Before the last glaciation (about 35-40 thousand. Years ago) via a land bridge in the area of ​​modern Bering Strait from Asia ancient hunters moved to North America, which settled to Tierra del Fuego. By the beginning of the Holocene, when the global warming and the melting of glaciers, many extinct large mammals - mammoths, woolly rhinoceros, cave bear. Apparently, this extinction was due not only to climate change, but human activity.

About 10 thousand. Years ago in warm temperate regions of the earth (the Mediterranean, Middle East, India, China, Mexico, Peru, and others.) Came the "Neolithic Revolution", associated with the transition from human hunting and gathering to agriculture and animal husbandry. Began the domestication of animals and the introduction of plants in culture.

Stormy human activities: plowing, stubbing and burning of forests, overgrazing and trampling herbage pets - has led to the extinction or reduction of many areas of steppe animals (tour tarpan et al.), The expansion of deserts (Sahara, Karakum Taklimakan ), the emergence of mobile sand.

All this determined the species composition of the organic world, which exists at the present time, influenced the modern geographical distribution of organisms, created their modern community. A huge role in the resettlement of species and speciation played as land bridges and insulation glaciers. Set of species and subspecies were formed during the Pleistocene and Holocene.

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