What is the geological period now? History of the geological development of the earth
I have long been interested in the history of our planet. After all, the world we see today was not always like this. It is difficult to even imagine what was on our planet many millions or even several billion years ago. Each period was characterized by some of its own characteristics.
What were the main eras and periods on our planet?
I’ll touch a little on the topic of eras and periods in general outline. So, scientists divide all 4.5 billion years like this.
- The Precambrian Era (Catarchaean, Archean and Proterozoic periods) - in terms of duration, this is the longest era, which lasted almost 4 billion years.
- Palaeozoic(includes six periods) - lasted a little less than 290 million years, at which time the conditions for life were finally formed, first in water and then on land.
- Mesozoic era(includes three periods) - the era of reptile dominance on our planet.
- The Cenozoic era (consists of the Paleogene, Neogene and Anthropocene periods) - we now live in this era, and to be more specific, in the Anthropocene.
Each era usually ended with some kind of cataclysm.
Mesozoic era
Almost everyone knows about this era, because many have seen the American film “Jurassic Park,” in which different breeds of dinosaurs appear. Yes, yes, these were the animals that dominated at that time.
The Mesozoic consists of the following segments:
- Triassic;
- Jurassic;
- chalky.
During the Jurassic period, dinosaurs reached greatest development. Were giant species, which reached a length of up to thirty meters. There were also very large and tall trees, and there is minimal vegetation on the ground. Ferns predominated among low-growing plants.
At the beginning of this era there was a single continent, but then it split into six parts, which over time took on its modern appearance.
Two million years before the extinction of the dinosaurs, the most formidable predator appeared - the Tyrannosaurus. And these reptiles became extinct after the earth collided with a comet. As a result, approximately 65% of all life on the planet died.
This era ended approximately sixty-five million years ago.
According to modern ideas, it is 4.5 - 5 billion years old. In the history of its occurrence, planetary and geological stages are distinguished.
Geological stage- sequence of events in the development of the Earth as planets since the formation of the earth's crust. During it, relief forms arose and were destroyed, the land submerged under water (the advance of the sea), the retreat of the sea, glaciations, the appearance and disappearance of various types animals and plants, etc.
Scientists, trying to reconstruct the history of the planet, study rock layers. They divide all deposits into 5 groups, distinguishing the following eras: Archean (ancient), Proterozoic (early), Paleozoic (ancient), Mesozoic (middle) and Cenozoic (new). The border between eras passes through the largest evolutionary events. The last three eras are divided into periods because in these deposits the remains of animals and plant remains were better preserved and in greater quantity.
Each era is characterized by events that had a decisive influence on modern life. relief.
Archean era was distinguished by violent volcanic activity, as a result of which igneous granite-containing rocks appeared on the surface of the Earth - the basis of future continents. At that time, the Earth was inhabited only by microorganisms that could live without oxygen. It is believed that the sediments of that era cover individual areas of land with an almost continuous shield; they contain a lot of iron, gold, silver, platinum and ores of other metals.
IN Proterozoic era volcanic activity was also high, the mountains of the so-called Baikal folding were formed. They have practically not been preserved and now represent only isolated small uplifts on the plains. During this period, the planet was inhabited by blue-green algae and protozoan microorganisms, and the first multicellular organisms arose. Proterozoic rock layers are rich in minerals: iron ores and ores of non-ferrous metals, mica.
At first Paleozoic era formed mountains Caledonian folding, which led to the reduction of sea basins and the emergence of large areas of land. Only isolated ridges of the Urals, Arabia, Southeast China and Central Europe. All these mountains are low, “worn out”. In the second half of the Paleozoic, the mountains of the Hercynian fold were formed. This era of mountain building was more powerful; vast mountain ranges arose in the territory Western Siberia and the Urals, Mongolia and Manchuria, most of Central Europe, east coast North America and Australia. Now they are represented by low blocky mountains. In the Paleozoic era, the Earth was inhabited by fish, amphibians and reptiles, and algae predominated among the vegetation. The main deposits of oil and coal arose during this period.
Mesozoic era began with a period of relative calm of the internal forces of the Earth, the gradual destruction of previously created mountain systems and submergence of flattened flat areas, such as most of Western Siberia. In the second half of the era, mountains of Mesozoic folding were formed. At this time, extensive mountainous countries, which even now have the appearance of mountains. These are the Cordillera, the mountains of Eastern Siberia, certain parts of Tibet and Indochina. The ground was covered with lush vegetation, which gradually died and rotted. In a hot and humid climate, swamps and peat bogs were actively formed. This was the age of the dinosaurs. Giant predatory and herbivorous animals have spread throughout almost the entire planet. The first mammals appeared at this time.
Cenozoic era continues to this day. Its beginning was marked by an increase in the activity of the Earth's internal forces, which led to a general rise of the surface. During the era of Alpine folding, young folded mountains arose within the Alpine-Himalayan belt and the continent of Eurasia acquired its modern shape. In addition, there was a rejuvenation of the ancient mountain ranges of the Urals, Appalachians, Tien Shan, and Altai. The climate on the planet changed sharply, and a period of powerful ice sheets began. Ice sheets advancing from the north changed the topography of the continents of the Northern Hemisphere, forming hilly plains with a large number of lakes.
The entire geological history of the Earth can be traced on a geochronological scale - a table of geological time, showing the sequence and subordination of the main stages of geology, the history of the Earth and the development of life on it (see Table 4 on pp. 46-49). The geochronological table should be read from bottom to top.
Questions and tasks to prepare for the exam
1. Explain why they are observed on Earth polar days and nights.
2. What would conditions be like on Earth if its axis of rotation were not inclined to the orbital plane?
3. The change of seasons on Earth is determined by two main reasons: the first is the rotation of the Earth around the Sun; name the second one.
4. How many times a year and when is the Sun at its zenith above the equator? Over the Northern Tropic? Over the South Tropic?
5. In what direction do constant winds deviate in the Northern Hemisphere and sea currents, moving in the meridional direction?
6. When is the shortest night in the Northern Hemisphere?
7. What are the characteristics of the days of the spring and autumn equinoxes on Earth? When do they occur in the Northern and Southern Hemispheres?
8. When are the days of summer and winter solstice in the Northern and Southern Hemispheres?
9. In what light zones is the territory of our country located?
10. List the geological periods of the Cenozoic era, starting with the most ancient.
Table 4
Geochronological scale
| Eras (duration - in million years) | Periods (duration in million years) | Major events history of the earth | Characteristic minerals formed in given time |
| 1 | 2 | 3 | 4 |
| Cenozoic 70 million years | Quaternary 2 Ma (Q) | General rise of land. Repeated glaciations, especially in the Northern Hemisphere. The emergence of man | Peat, placer deposits of gold, diamonds, precious stones |
| Neogene 25 Ma (N) | The emergence of young mountains in areas of Alpine folding. Rejuvenation of mountains in areas of all ancient folds. Dominance of flowering plants | Brown coals, oil, amber | |
| Paleogene 41 Ma (P) | Destruction of the mountains of Mesozoic folding. Widespread development of flowering plants, birds and mammals | Phosphorites, brown coals, bauxites |
| Mesozoic 165 Ma | Cretaceous 70 Ma (K) | The emergence of young mountains in areas of Mesozoic folding. Extinction of giant reptiles (dinosaurs). Development of birds and mammals | Oil, oil shale, chalk, coal, phosphorites |
| Jurassic 50 Ma (J) | Formation of modern oceans. Hot and humid climate on most of the land. The rise of giant reptiles (dinosaurs). Dominance of gymnosperms | Hard coals, oil, phosphorites | |
| Triassic 40 Ma (T) | The greatest retreat of the sea and rise of land in the entire history of the Earth. Destruction of the mountains of the Caledonian and Hercynian folds. Vast deserts. First mammals | Rock salts | |
| 1 | 2 | 3 | 4 |
| Paleozoic 330 million years | Permian 45 Ma (P) | The emergence of young folded mountains in the areas of the Hercynian fold. Dry climate over most of the land. The emergence of gymnosperms | Rock and potassium salts, gypsum |
| Carboniferous 65 Ma (C) | Hot and humid climate over most of the land. Widespread marshy lowlands in coastal areas. Forests of tree ferns. The first reptiles, the rise of amphibians | Coal, oil | |
| Devonian 55 Ma (r) | Hot climate over most of the land. The first deserts. The appearance of amphibians. Numerous fish | Salts, oil | |
| Silurian 35 Ma (S) | The emergence of young folded mountains in the areas of the Caledonian folding. The first land plants (mosses and ferns) | |
| | Ordovician 60 Ma (O) | Reducing the area of sea basins. Appearance of the first terrestrial invertebrates | |
| Cambrian 70 Ma | The emergence of young mountains in the areas of the Baikal fold. Flooding of vast areas by seas. The flourishing of marine invertebrates | Rock salt, gypsum, phosphorites | |
| Proterozoic era 600 million years | The beginning of the Baikal folding. Powerful volcanism. Development of bacteria and blue-green algae | Iron ores, mica, graphite | |
| Archean era 900 million years | Formation of the continental crust. Intense volcanic activity. The time of primitive single-celled bacteria | Ore | |
Maksakovsky V.P., Petrova N.N., Physical and economical geography peace. - M.: Iris-press, 2010. - 368 pp.: ill.
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Sedimentary rocks accumulate on earth's surface, occupy over 75% of the land surface area. More than 95% of their volume accumulated in marine conditions. Most sedimentary rocks characterized by a layered texture, reflecting the periodicity of sedimentation. The nature of layering depends on the specific conditions of the process, and the primary one is the dynamics of the environment. Thus, in stagnant water, horizontal layering occurs, and in a river flow, inclined layering occurs. Another characteristic textural feature is porosity. The texture of sedimentary rocks is most often porous and compact (non-porous). Depending on the pore size, porosity is divided into coarse, coarse, fine and fine.
In the case of an accumulation of more or less identical particles, the structure is called uniform-grained; otherwise, it is called heterogranular. According to the shape of the particles, rocks have a rounded and unrounded structure.
Chemical rocks are characterized by oolitic (grains are spherical), acicular, fibrous, leafy and granular structures. Breeds organic origin, consisting of well-preserved shells or plants, have a biomorphic structure.
If sedimentary rocks are an accumulation of individual particles not connected to each other, they are called granular. When individual larger particles are held together by a fine-grained material called cement, the rocks are called cemented and are characterized by a compact texture. Cementation of rocks can occur simultaneously with their formation, as well as after, as a result of the precipitation of various salts from solutions circulating through the pores. Based on their composition, they distinguish between clay, bitumen, lime, ferruginous, siliceous and other cements. The nature of cement largely determines the density and strength of cemented rocks. Rocks with clay cement are considered the weakest, while rocks with siliceous cement are the strongest.
Based on their origin, sedimentary rocks can be divided into five groups.
Clastic (clastic) rocks are formed as a result of mechanical destruction of any other rocks. They are classified according to three criteria. 1. By size (diameter) of fragments: coarse clastic (psephites), medium clastic (psammites) and fine clastic (silts). 2. According to the shape of the fragments: angular (crushed stone) and rounded (pebbles). 3. According to the presence of cement: loose (sand) and cemented (sandstone).
Clay rocks (pelites) consist of tiny particles, the diameter of which is less than 0.01 mm. Most of them arise due to chemical weathering processes. The accumulation of clays is associated with the precipitation of matter from colloidal solutions, due to which the clays are characterized by thin horizontal layering. When clays dehydrate, dense mudstones that do not soak in water appear.
Chemogenic rocks arise when a substance crystallizes from supersaturated aqueous solutions. For the most part, chemogenic rocks are monomineral: they consist of minerals of the classes of carbonates (chemogenic limestones), sulfates (gypsum and anhydrite), halides (rock and potassium salts), etc. Chemogenic rocks are characterized by a fully crystalline (crystalline-granular) structure: from coarse to fine crystalline , and even cryptocrystalline. Their texture is both layered and homogeneously massive.
Organogenic rocks are formed due to the accumulation of waste products of organisms: primarily marine and, to a lesser extent, freshwater invertebrates. Some organogenic rocks arise from the accumulation of plant remains (peat). In terms of mineral composition, carbonate rocks (limestone-shell rock, chalk) predominate; siliceous rocks (diatomite) and other organogenic rocks are less common. Among characteristic structures it is necessary to call it biomorphic (the rock consists of undisturbed skeletons), detritus (the rock consists of crushed skeletons), biomorphic - detritus (the rock is composed of both intact and destroyed skeletons). The texture of organogenic rocks is layered and porous.
Sedimentary rocks of mixed origin have a complex composition and arise under the combined influence of different processes. Among the mixed species, marl and opoka should be mentioned.
The history of the Earth is divided into large periods of time called geological eras; eras (with the exception of the most ancient) are divided into geological periods, and those, in turn, into epochs. The boundaries between these divisions correspond to various kinds of changes of a geological and biological (paleontological) nature: increased volcanism and mountain-building processes; uplifts or subsidences of significant areas of the continental crust, leading to corresponding invasions or retreats of the sea (marine transgressions and regressions); significant changes in fauna and flora, etc.
The geological history of the Earth is divided into large intervals - eras, eras - into periods, periods - into centuries. The division into eras, periods and centuries is, of course, relative, because there were no sharp distinctions between these divisions. But still, it was at the turn of neighboring eras and periods that significant geological transformations took place - mountain-building processes, redistribution of land and sea, climate change, etc. In addition, each division was characterized by the qualitative originality of flora and fauna.
The deposits of the most ancient Archeozoic and Proterozoic eras contain extremely few fossil remains of organisms; on this basis, the Archeozoic and Proterozoic are often combined under the name “cryptozoic” (the stage of hidden life), in contrast to the three subsequent eras - the Paleozoic, Mesozoic and Cenozoic, united as the “Phanerozoic” (the stage of obvious, observable life).
Geological eras of Earth's history:
· catarchaea (from the formation of the Earth 5 billion years ago to the origin of life)
An era when there was a lifeless Earth, shrouded in an atmosphere devoid of oxygen, poisonous to living beings; Volcanic eruptions thundered, lightning flashed, hard ultraviolet radiation penetrated the atmosphere and upper layers of water. Under the influence of these phenomena, the first organic compounds begin to be synthesized from the mixture of hydrogen sulfide, ammonia, and carbon monoxide vapors that enveloped the Earth, and properties characteristic of life appear.
archaea, ancient era(3.8 billion - 2.6 billion years)
The primary crust, formed as a result of the cooling of the Earth, was continuously destroyed by steam and gas, which were released by the hot substance. Lava erupted by millions of volcanoes solidified on the surface, forming primary mountains and plateaus, continents and oceanic depressions. The powerful, dense atmosphere also cooled, resulting in heavy rainfall. On the hot earth's surface they instantly turned into steam. Solid clouds enveloped the Earth, preventing the passage of the sun's rays, warming its surface. The solid crust cooled, the oceanic depressions filled with water. The primary ocean, rivers, and atmosphere destroyed the primary mountains and continents, forming the first sedimentary rocks. Now they are hard and dense. The formation of many minerals is associated with them: building stone, mica, nickel ore, kaolin, gold, molybdenum, copper, cobalt, radioactive minerals, iron. In the Archean era, various flows occurred in the warm waters of the primary ocean. chemical reactions between salts, alkalis and acids. They were favored solar radiation, dense atmosphere, ionization of water caused by huge lightning discharges. At the end of the Archean era, lumps of protein matter appeared in the seas, marking the beginning of all life on Earth.
Proterozoic (2.6 billion - 570 million years)
The coal-like material shungite was found in Proterozoic deposits. This indicates the appearance in the Proterozoic era of plants, from the remains of which coal was formed. Marble deposits suggest that animals with calcareous shells lived in the Proterozoic. Over time, the limestones formed from the deposits of these shells turned into marble. Proterozoic rocks contain deposits of the sea, land, rivers, mountains, deserts and glaciers. Consequently, the climate of the Proterozoic was quite diverse. The marine sediments are covered by volcanic sediments, which are also overlain by marine sediments. Periods of quiet development of the Proterozoic earth's crust were replaced by violent mountain-building processes. Many minerals are associated with Proterozoic deposits: iron ores, marble, graphite, nickel ore, piezoquartz, kaolin, gold, mica, talc, molybdenum, copper, bismuth, tungsten, cobalt, radioactive minerals, precious stones. At the end of the Proterozoic, thanks to mountain-building processes, mountains arose in place of the sea, and sedimentary deposits metamorphosed. The end of the Proterozoic is sometimes called the “age of jellyfish” - representatives of the coelenterates that were very common at that time.
Paleozoic (570 million - 230 million years) with next periods: Cambrian (570 million - 500 million years); Ordovician (500 million - 440 million years); Silurian (440 million - 410 million years); Devonian (410 million - 350 million years); Carboniferous (350 million - 285 million years); Permian (285 million - 230 million years);
The Paleozoic era of the Earth's development is divided into two large stages: the Early Paleozoic, which began in the Late Riphean and Vendian and ended in the Silurian period, and the Late Paleozoic, which included the Devonian, Carboniferous and Permian periods. Each of them in the mobile belts ended with folding - Caledonian and Hercynian, as a result of which extended mountain-folded areas and systems were formed, attached to stable platforms and “fused” with them. The mountain-building period that began at the end of the Silurian changed the climate and the living conditions of organisms. As a result of the rise of land and the reduction of seas, the Devonian climate was more continental than in the Silurian. In the Devonian, desert and semi-desert regions appeared; The first forests of giant ferns, horsetails and club mosses appear on land. New groups of animals begin to conquer land. The end of the Carboniferous period saw the appearance of the first reptiles - completely terrestrial representatives of vertebrates. They achieved significant diversity in the Permian due to the arid climate and cooling.
· Mesozoic (230 million - 67 million years) with the following periods: Triassic (230 million - 195 million years); Jurassic (195 million - 137 million years); Cretaceous (137 million - 67 million years)
The Mesozoic is rightly called the era of reptiles. Their heyday and extinction occur precisely in this era. In the Mesozoic, the climate becomes more arid. Many land organisms, in which certain stages of life are associated with water, are dying out. Instead, terrestrial forms begin to predominate. In the Triassic, gymnosperms reached strong development among plants, and reptiles among animals. In the Triassic, herbivores and carnivorous dinosaurs. Marine reptiles are very diverse in this era. In the Jurassic, reptiles began to master the air environment. Flying lizards survived until the end of the Cretaceous. In the Jurassic, birds also evolved from reptiles. On land in the Jurassic, giant herbivorous dinosaurs are found. In the second half of the Cretaceous, marsupials and placental mammals arose. The acquisition of viviparity and warm-bloodedness were the aromorphoses that ensured the progress of mammals.
Cenozoic (67 million - up to our time) with the following periods and centuries:
– Paleogene (67 million - 27 million years): Paleocene (67-54 million years), Eocene (54-38 million years), Oligocene (38-27 million years);
– Neogene (27 million - 3 million years): Miocene (27-8 million years), Pliocene (8-3 million years);
– Quaternary (3 million - our time): Pleistocene (3 million - 20 thousand years), Holocene (20 thousand years - our time).
The geological era in which we live is called the Cenozoic. This is the era of flowering plants, insects, birds and mammals. The Cenozoic is divided into two unequal periods: Tertiary (67-3 million years) and Quaternary (3 million years - our time). In the first half of the Tertiary period, tropical and subtropical forests were widespread. By the middle of this period, common ancestral forms became widespread great apes and people. By the end of the Tertiary period, representatives of all modern families of animals and plants and the vast majority of genera are found.
At this time, the great process of steppeification of the land began, which led to the extinction of some tree and forest forms and to the emergence of others into open space. Mammoths became extinct during the Quaternary period. saber tooth tigers, giant sloths, big-horned turf deer and other animals. Ancient hunters played a major role in the extinction of large mammals.
The emergence of the Earth and the early stages of its formation
One of the important tasks of modern natural science in the field of Earth sciences is to restore the history of its development. According to modern cosmogonic concepts, the Earth was formed from gas and dust matter scattered in the protosolar system. One of the most likely options for the emergence of the Earth is as follows. First, the Sun and a flattened rotating circumsolar nebula were formed from an interstellar gas and dust cloud under the influence, for example, of the explosion of a nearby supernova. Next, the evolution of the Sun and the circumsolar nebula occurred with the transfer of angular momentum from the Sun to the planets by electromagnetic or turbulent-convective methods. Subsequently, the “dusty plasma” condensed into rings around the Sun, and the material of the rings formed the so-called planetesimals, which condensed into planets. After this, a similar process was repeated around the planets, leading to the formation of satellites. It is believed that this process took about 100 million years.
It is assumed that further, as a result of differentiation of the Earth's substance under the influence of its gravitational field and radioactive heating, shells of the Earth, different in chemical composition, state of aggregation and physical properties, emerged and developed - the Earth's geosphere. The heavier material formed a core, probably composed of iron mixed with nickel and sulfur. Some lighter elements remained in the mantle. According to one hypothesis, the mantle is composed of simple oxides of aluminum, iron, titanium, silicon, etc. The composition of the earth's crust has already been discussed in some detail in § 8.2. It is composed of lighter silicates. Even lighter gases and moisture formed the primary atmosphere.
As already mentioned, it is assumed that the Earth was born from a cluster of cold solid particles that fell out of a gas-dust nebula and stuck together under the influence of mutual attraction. As the planet grew, it heated up due to the collision of these particles, which reached several hundred kilometers, like modern asteroids, and the release of heat not only by the naturally radioactive elements now known to us in the crust, but also by more than 10 radioactive isotopes AI, Be, that have become extinct since then. Cl, etc. As a result, complete (in the core) or partial (in the mantle) melting of the substance could occur. In the initial period of its existence, up to approximately 3.8 billion years, the Earth and other terrestrial planets, as well as the Moon, were subjected to intense bombardment by small and large meteorites. The consequence of this bombardment and the earlier collision of planetesimals could be the release of volatiles and the beginning of the formation of a secondary atmosphere, since the primary one, consisting of gases captured during the formation of the Earth, most likely quickly dissipated into outer space. Somewhat later, the hydrosphere began to form. The atmosphere and hydrosphere thus formed were replenished during the process of degassing of the mantle during volcanic activity.
The fall of large meteorites created extensive and deep craters, similar to those currently observed on the Moon, Mars, and Mercury, where their traces have not been erased by subsequent changes. Cratering could provoke outpourings of magma with the formation of basalt fields similar to those covering the lunar “seas”. This is probably how the primary crust of the Earth was formed, which, however, was not preserved on its modern surface, with the exception of relatively small fragments in the “younger” continental-type crust.
This crust, which already contains granites and gneisses, although with a lower content of silica and potassium than in “normal” granites, appeared at the turn of about 3.8 billion years and is known to us from outcrops within the crystalline shields of almost all continents. The method of formation of the oldest continental crust is still largely unclear. In the composition of this crust, which is everywhere metamorphosed under conditions of high temperatures and pressures, rocks are found whose textural features indicate accumulation in an aquatic environment, i.e. in this distant era the hydrosphere already existed. The emergence of the first crust, similar to the modern one, required the supply of large quantities of silica, aluminum, and alkalis from the mantle, while now mantle magmatism creates a very limited volume of rocks enriched in these elements. It is believed that 3.5 billion years ago, gray gneiss crust, named after the predominant type of rocks composing it, was widespread across the area of modern continents. In our country, for example, it is known on the Kola Peninsula and in Siberia, in particular in the river basin. Aldan.
Principles of periodization of the geological history of the Earth
Subsequent events in geological time are often determined according to relative geochronology, categories “ancient”, “younger”. For example, some era is older than some other. Individual segments of geological history are called (in order of decreasing duration) zones, eras, periods, epochs, centuries. Their identification is based on the fact that geological events are imprinted in rocks, and sedimentary and volcanogenic rocks are located in layers in the earth's crust. In 1669, N. Stenoi established the law of bedding sequence, according to which the underlying layers of sedimentary rocks are older than the overlying ones, i.e. formed before them. Thanks to this, it became possible to determine the relative sequence of formation of layers, and therefore the geological events associated with them.
The main one in relative geochronology is the biostratigraphic, or paleontological, method of establishing the relative age and sequence of occurrence of rocks. This method was proposed by W. Smith at the beginning of the 19th century, and then developed by J. Cuvier and A. Brongniard. The fact is that in most sedimentary rocks you can find the remains of animal or plant organisms. J.B. Lamarck and Charles Darwin established that animal and plant organisms over the course of geological history gradually improved in the struggle for existence, adapting to changing living conditions. Some animal and plant organisms died out at certain stages of the Earth's development, and were replaced by others, more advanced ones. Thus, from the remains of previously living, more primitive ancestors found in some layer, one can judge the relatively more ancient age of this layer.
Another method of geochronological division of rocks, especially important for the division of igneous formations of the ocean floor, is based on the property of magnetic susceptibility of rocks and minerals formed in the Earth's magnetic field. With a change in rock orientation relative to magnetic field or the field itself, part of the “innate” magnetization is preserved, and the change in polarity is reflected in a change in the orientation of the remanent magnetization of the rocks. Currently, a scale of change of such eras has been established.
Absolute geochronology - the study of the measurement of geological time expressed in ordinary absolute astronomical units(years) - determines the time of occurrence, completion and duration of all geological events, primarily the time of formation or transformation (metamorphism) of rocks and minerals, since the age of geological events is determined by their age. The main method here is to analyze the ratio of radioactive substances and their decay products in rocks formed in different eras.
The oldest rocks are currently established in Western Greenland (3.8 billion years old). The longest age (4.1 - 4.2 billion years) was obtained from zircons from Western Australia, but the zircon here occurs in a redeposited state in Mesozoic sandstones. Taking into account the ideas about the simultaneous formation of all planets of the Solar system and the Moon and the age of the most ancient meteorites (4.5-4.6 billion years) and ancient lunar rocks (4.0-4.5 billion years), the age of the Earth is taken to be 4.6 billion years
In 1881, at the II International Geological Congress in Bologna (Italy), the main divisions of combined stratigraphic (for separating layered sedimentary rocks) and geochronological scales were approved. According to this scale, the history of the Earth was divided into four eras in accordance with the stages of development of the organic world: 1) Archean, or Archeozoic - the era of ancient life; 2) Paleozoic - the era of ancient life; 3) Mesozoic - era average life; 4) Cenozoic - era of new life. In 1887, the Proterozoic era was distinguished from the Archean era - the era of primary life. Later the scale was improved. One of the options for the modern geochronological scale is presented in Table. 8.1. The Archean era is divided into two parts: early (older than 3500 million years) and late Archean; Proterozoic - also into two: early and late Proterozoic; in the latter, the Riphean (the name comes from the ancient name of the Ural Mountains) and Vendian periods are distinguished. The Phanerozoic zone is divided into Paleozoic, Mesozoic and Cenozoic eras and consists of 12 periods.
Table 8.1. Geochronological scale
|
Age (beginning), |
|||
|
Phanerozoic |
Cenozoic |
Quaternary | |
|
Neogene | |||
|
Paleogene | |||
|
Mesozoic | |||
|
Triassic | |||
|
Paleozoic |
Permian | ||
|
Coal | |||
|
Devonian | |||
|
Silurian | |||
|
Ordovician | |||
|
Cambrian | |||
|
cryptozoic |
Proterozoic |
Vendian | |
|
Riphean | |||
|
Karelian | |||
|
Archean | |||
|
Catarhean |
The main stages of the evolution of the earth's crust
Let us briefly consider the main stages of the evolution of the earth's crust as an inert substrate on which the diversity of the surrounding nature developed.
INapxee The still quite thin and plastic crust, under the influence of stretching, experienced numerous discontinuities through which basaltic magma again rushed to the surface, filling troughs hundreds of kilometers long and many tens of kilometers wide, known as greenstone belts (they owe this name to the predominant greenschist low-temperature metamorphism of basaltic rocks). breeds). Along with basalts, among the lavas of the lower, most powerful part of the section of these belts, there are high-magnesium lavas, indicating a very high degree of partial melting of mantle matter, which indicates a high heat flow, much higher than today. The development of greenstone belts consisted of a change in the type of volcanism in the direction of an increase in the content of silicon dioxide (SiO 2), in compression deformations and metamorphism of sedimentary-volcanogenic fulfillment, and, finally, in the accumulation of clastic sediments, indicating the formation of mountainous terrain.
After the change of several generations of greenstone belts, the Archean stage of the evolution of the earth's crust ended 3.0 -2.5 billion years ago with the massive formation of normal granites with a predominance of K 2 O over Na 2 O. Granitization, as well as regional metamorphism, which in some places reached the highest level, led to the formation of mature continental crust over most of the area of modern continents. However, this crust also turned out to be insufficiently stable: at the beginning of the Proterozoic era it experienced fragmentation. At this time, a planetary network of faults and cracks arose, filled with dikes (plate-shaped geological bodies). One of them, the Great Dyke in Zimbabwe, is more than 500 km long and up to 10 km wide. In addition, rifting appeared for the first time, giving rise to zones of subsidence, powerful sedimentation and volcanism. Their evolution led to the creation at the end early Proterozoic(2.0-1.7 billion years ago) folded systems that again welded together fragments of the Archean continental crust, which was facilitated by a new era of powerful granite formation.
As a result, by the end of the Early Proterozoic (at the turn of 1.7 billion years ago), mature continental crust already existed on 60-80% of the area of its modern distribution. Moreover, some scientists believe that at this turn the entire continental crust formed a single massif - the supercontinent Megagaea (big earth), which was opposed by the ocean on the other side of the globe - the predecessor of the modern Pacific Ocean- Megathalassa (big sea). This ocean was less deep than modern oceans, because the growth of the volume of the hydrosphere due to degassing of the mantle in the process of volcanic activity continues throughout the subsequent history of the Earth, although more slowly. It is possible that the prototype of Megathalassa appeared even earlier, at the end of the Archean.
In the Catarchean and early Archean, the first traces of life appeared - bacteria and algae, and in the late Archean, algal calcareous structures - stromatolites - spread. In the Late Archean, a radical change in the composition of the atmosphere began, and in the Early Proterozoic ended: under the influence of plant activity, free oxygen appeared in it, while the Catarchean and Early Archean atmosphere consisted of water vapor, CO 2, CO, CH 4, N, NH 3 and H 2 S with an admixture of HC1, HF and inert gases.
In the Late Proterozoic(1.7-0.6 billion years ago) Megagaia began to gradually split, and this process sharply intensified at the end of the Proterozoic. Its traces are extended continental rift systems buried at the base of the sedimentary cover of ancient platforms. Its most important result was the formation of vast intercontinental mobile belts - the North Atlantic, Mediterranean, Ural-Okhotsk, which divided the continents of North America, Eastern Europe, East Asia and the largest fragment of Megagaea - the southern supercontinent Gondwana. The central parts of these belts developed on the newly formed ocean crust during rifting, i.e. the belts represented ocean basins. Their depth gradually increased as the hydrosphere grew. At the same time, mobile belts developed along the periphery of the Pacific Ocean, the depth of which also increased. Climatic conditions became more contrasting, as evidenced by the appearance, especially at the end of the Proterozoic, of glacial deposits (tillites, ancient moraines and fluvio-glacial sediments).
Paleozoic stage The evolution of the earth's crust was characterized by the intensive development of mobile belts - intercontinental and continental margins (the latter on the periphery of the Pacific Ocean). These belts were divided into marginal seas and island arcs, their sedimentary-volcanogenic strata experienced complex fold-thrust and then normal fault deformations, granites were intruded into them and folded mountain systems were formed on this basis. This process was uneven. It distinguishes a number of intense tectonic epochs and granite magmatism: Baikal - at the very end of the Proterozoic, Salair (from the Salair ridge to Central Siberia) - at the end of the Cambrian, Takovian (from the Takovsky Mountains in the eastern USA) - at the end of the Ordovician, Caledonian (from the ancient Roman name for Scotland) - at the end of the Silurian, Acadian (Acadia - old name northeastern states of the USA) - in the middle of the Devonian, Sudeten - at the end of the Early Carboniferous, Saale (from the Saale River in Germany) - in the middle of the Early Permian. The first three tectonic eras of the Paleozoic are often combined into the Caledonian era of tectogenesis, the last three - into the Hercynian or Variscan. In each of the listed tectonic epochs, certain parts of the mobile belts turned into folded mountain structures, and after destruction (denudation) they became part of the foundation of young platforms. But some of them partially experienced activation in subsequent eras of mountain building.
By the end of the Paleozoic, the intercontinental mobile belts were completely closed and filled with folded systems. As a result of the withering away of the North Atlantic belt, the North American continent closed with the East European continent, and the latter (after the completion of the development of the Ural-Okhotsk belt) with the Siberian continent, and the Siberian continent with the Chinese-Korean one. As a result, the supercontinent Laurasia was formed, and the death of the western part of the Mediterranean belt led to its unification with the southern supercontinent - Gondwana - into one continental block - Pangea. At the end of the Paleozoic - beginning of the Mesozoic, the eastern part of the Mediterranean belt turned into a huge bay of the Pacific Ocean, along the periphery of which folded mountain structures also rose.
Against the background of these changes in the structure and topography of the Earth, the development of life continued. The first animals appeared in the late Proterozoic, and at the very dawn of the Phanerozoic, almost all types of invertebrates existed, but they were still devoid of shells or shells, which have been known since the Cambrian. In the Silurian (or already in the Ordovician), vegetation began to emerge on land, and at the end of the Devonian, forests existed, which became most widespread in the Carboniferous period. Fish appeared in the Silurian, amphibians - in the Carboniferous.
Mesozoic and Cenozoic eras - the last major stage in the development of the structure of the earth's crust, which is marked by the formation of modern oceans and the separation of modern continents. At the beginning of the stage, in the Triassic, Pangea still existed, but already in the early Jurassic period it again split into Laurasia and Gondwana due to the emergence of the latitudinal Tethys Ocean, stretching from Central America to Indochina and Indonesia, and in the west and east it connected with the Pacific Ocean (Fig. 8.6); this ocean included the Central Atlantic. From here, at the end of the Jurassic, the process of continental separation spread to the north, creating during Cretaceous period and early Paleogene the North Atlantic, and starting from the Paleogene - the Eurasian basin of the Arctic Ocean (the Amerasian basin arose earlier as part of the Pacific Ocean). As a result, North America separated from Eurasia. In the Late Jurassic, the formation of the Indian Ocean began, and from the beginning of the Cretaceous, the South Atlantic began to open from the south. This marked the beginning of the collapse of Gondwana, which existed as a single entity throughout the Paleozoic. At the end of the Cretaceous, the North Atlantic joined the South Atlantic, separating Africa from South America. At the same time, Australia separated from Antarctica, and at the end of the Paleogene the latter separated from South America.
Thus, by the end of the Paleogene, all modern oceans took shape, all modern continents became isolated, and the appearance of the Earth acquired a form that was basically close to the present one. However, there were no modern mountain systems yet.
Intense mountain building began in the late Paleogene (40 million years ago), culminating in the last 5 million years. This stage of the formation of young fold-cover mountain structures and the formation of revived arched block mountains is identified as neotectonic. In fact, the neotectonic stage is a substage of the Mesozoic-Cenozoic stage of the Earth's development, since it was at this stage that the main features of the modern relief of the Earth took shape, starting with the distribution of oceans and continents.
At this stage, the formation of the main features of modern fauna and flora was completed. The Mesozoic era was the era of reptiles, mammals became dominant in the Cenozoic, and humans appeared in the late Pliocene. At the end of the Early Cretaceous, angiosperms appeared and the land acquired grass cover. At the end of the Neogene and Anthropocene, the high latitudes of both hemispheres were covered by powerful continental glaciation, relics of which are the ice caps of Antarctica and Greenland. This was the third major glaciation in the Phanerozoic: the first took place in the Late Ordovician, the second at the end of the Carboniferous - beginning of the Permian; both of them were distributed within Gondwana.
QUESTIONS FOR SELF-CONTROL
What are spheroid, ellipsoid and geoid? What are the parameters of the ellipsoid adopted in our country? Why is it needed?
What's it like internal structure Earth? On what basis is a conclusion made about its structure?
What are the main physical parameters Earths and how do they change with depth?
What is the chemical and mineralogical composition of the Earth? On what basis is a conclusion made about the chemical composition of the entire Earth and the earth’s crust?
What are the main types of the earth's crust currently distinguished?
What is the hydrosphere? What is the water cycle in nature? What are the main processes occurring in the hydrosphere and its elements?
What is atmosphere? What is its structure? What processes occur within its boundaries? What is weather and climate?
Define endogenous processes. What endogenous processes do you know? Briefly describe them.
What is the essence of plate tectonics? What are its main provisions?
10. Define exogenous processes. What is the main essence of these processes? What endogenous processes do you know? Briefly describe them.
11. How do endogenous and exogenous processes interact? What are the results of the interaction of these processes? What is the essence of the theories of V. Davis and V. Penk?
What are modern ideas about the origin of the Earth? How did its early formation as a planet occur?
What is the basis for periodization of the geological history of the Earth?
14. How it developed Earth's crust in the geological past of the Earth? What are the main stages in the development of the earth's crust?
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The history of our planet still holds many mysteries. Scientists from various fields of natural science have contributed to the study of the development of life on Earth.
Our planet is believed to be about 4.54 billion years old. This entire time period is usually divided into two main stages: Phanerozoic and Precambrian. These stages are called eons or eonothema. Eons, in turn, are divided into several periods, each of which is distinguished by a set of changes that occurred in the geological, biological, and atmospheric state of the planet.
- Precambrian, or cryptozoic is an eon (time period in the development of the Earth), covering about 3.8 billion years. That is, the Precambrian is the development of the planet from the moment of formation, the formation of the earth’s crust, the proto-ocean and the emergence of life on Earth. By the end of the Precambrian, highly organized organisms with a developed skeleton were already widespread on the planet.
The eon includes two more eonothems - catarchaean and archaean. The latter, in turn, includes 4 eras.
1. Katarhey- this is the time of the formation of the Earth, but there was no core or crust yet. The planet was still a cold cosmic body. Scientists suggest that during this period there was already water on Earth. The Catarchaean lasted about 600 million years.
2. Archaea covers a period of 1.5 billion years. During this period, there was no oxygen on Earth yet, and deposits of sulfur, iron, graphite, and nickel were being formed. The hydrosphere and the atmosphere were a single vapor-gas shell, which enveloped in a dense cloud Earth. The sun's rays practically did not penetrate through this curtain, so darkness reigned on the planet. 2.1 2.1. Eoarchaean- this is the first geological era, which lasted about 400 million years. The most important event of the Eoarchean was the formation of the hydrosphere. But there was still little water, the reservoirs existed separately from each other and did not yet merge into the world ocean. At the same time, the earth's crust becomes solid, although asteroids are still bombarding the earth. At the end of the Eoarchean, the first supercontinent in the history of the planet, Vaalbara, formed.
2.2 Paleoarchean- the next era, which also lasted approximately 400 million years. During this period, the Earth's core is formed and the magnetic field strength increases. A day on the planet lasted only 15 hours. But the oxygen content in the atmosphere increases due to the activity of emerging bacteria. Remains of these first forms of Paleoarchean life have been found in Western Australia.
2.3 Mesoarchean also lasted about 400 million years. During the Mesoarchean era, our planet was covered by a shallow ocean. The land areas were small volcanic islands. But already during this period the formation of the lithosphere begins and the mechanism of plate tectonics begins. At the end of the Mesoarchean the first glacial period, during which snow and ice first form on Earth. Biological species are still represented by bacteria and microbial life forms.
2.4 Neoarchaean- the final era of the Archean eon, the duration of which is about 300 million years. Colonies of bacteria at this time form the first stromatolites (limestone deposits) on Earth. The most important event of the Neoarchean was the formation of oxygen photosynthesis.
II. Proterozoic- one of the longest time periods in the history of the Earth, which is usually divided into three eras. During the Proterozoic, the ozone layer appears for the first time, and the world ocean reaches almost its modern volume. And after the long Huronian glaciation, the first multicellular life forms appeared on Earth - mushrooms and sponges. The Proterozoic is usually divided into three eras, each of which contained several periods.
3.1 Paleo-Proterozoic- the first era of the Proterozoic, which began 2.5 billion years ago. At this time, the lithosphere is fully formed. But the previous forms of life practically died out due to an increase in oxygen content. This period was called the oxygen catastrophe. By the end of the era, the first eukaryotes appear on Earth.
3.2 Meso-Proterozoic lasted approximately 600 million years. The most important events of this era: the formation of continental masses, the formation of the supercontinent Rodinia and the evolution of sexual reproduction.
3.3 Neo-Proterozoic. During this era, Rodinia breaks up into approximately 8 parts, the superocean of Mirovia ceases to exist, and at the end of the era, the Earth is covered with ice almost to the equator. In the Neoproterozoic era, living organisms for the first time begin to acquire a hard shell, which will later serve as the basis of the skeleton.
III. Paleozoic- the first era of the Phanerozoic eon, which began approximately 541 million years ago and lasted about 289 million years. This is the era of the emergence of ancient life. The supercontinent Gondwana unites southern continents, a little later the rest of the land joins it and Pangea appears. Climatic zones begin to form, and the flora and fauna are represented mainly by marine species. Only towards the end of the Paleozoic did land development begin and the first vertebrates appeared.
The Paleozoic era is conventionally divided into 6 periods.
1. Cambrian period lasted 56 million years. During this period, the main rocks are formed, and a mineral skeleton appears in living organisms. And the most important event of the Cambrian is the emergence of the first arthropods.
2. Ordovician period- the second period of the Paleozoic, which lasted 42 million years. This is the era of the formation of sedimentary rocks, phosphorites and oil shale. Organic world The Ordovician is represented by marine invertebrates and blue-green algae.
3. Silurian period covers the next 24 million years. At this time, almost 60% of living organisms that existed before die out. But the first cartilaginous bones and bones in the history of the planet appear bony fish. On land, the Silurian is marked by the appearance of vascular plants. Supercontinents are moving closer together and forming Laurasia. By the end of the period, ice melted, sea levels rose, and the climate became milder.
4. Devonian period is characterized by the rapid development of diverse life forms and the development of new ecological niches. The Devonian covers a time period of 60 million years. The first terrestrial vertebrates, spiders, and insects appear. Sushi animals develop lungs. Although, fish still predominate. The flora kingdom of this period is represented by propferns, horsetails, mosses and gosperms.
5. Carboniferous period often called carbon. At this time, Laurasia collides with Gondwana and a new supercontinent Pangea appears. A new ocean is also formed - Tethys. This is the time of the appearance of the first amphibians and reptiles.
6. Permian period- the last period of the Paleozoic, ending 252 million years ago. It is believed that at this time a large asteroid fell on Earth, which led to significant climate change and the extinction of almost 90% of all living organisms. Most of the land is covered with sand, and the most extensive deserts appear that have ever existed in the entire history of the development of the Earth.
IV. Mesozoic- the second era of the Phanerozoic eon, which lasted almost 186 million years. At this time, the continents acquired almost modern outlines. A warm climate contributes to the rapid development of life on Earth. Giant ferns disappear and are replaced by angiosperms. The Mesozoic is the era of dinosaurs and the appearance of the first mammals.
IN Mesozoic era There are three periods: Triassic, Jurassic and Cretaceous.
1. Triassic lasted just over 50 million years. At this time, Pangea begins to break up, and inland seas gradually become smaller and dry out. The climate is mild, the zones are not clearly defined. Almost half of the land's plants are disappearing as deserts spread. And in the kingdom of fauna the first warm-blooded and land reptiles appeared, which became the ancestors of dinosaurs and birds.
2. Jurassic covers a span of 56 million years. The Earth had a humid and warm climate. The land is covered with thickets of ferns, pines, palms, and cypresses. Dinosaurs reign on the planet, and numerous mammals were still distinguished by their small stature and thick hair.
3. Cretaceous period- the longest period of the Mesozoic, lasting almost 79 million years. The separation of the continents is almost ending, the Atlantic Ocean is significantly increasing in volume, and ice sheets are forming at the poles. Increase water mass oceans leads to the formation greenhouse effect. At the end of the Cretaceous period, a catastrophe occurs, the causes of which are still not clear. As a result, all dinosaurs and most species of reptiles and gymnosperms became extinct.
V. Cenozoic- this is the era of animals and homo sapiens, which began 66 million years ago. At this time, the continents acquired their modern shape, Antarctica occupied the south pole of the Earth, and the oceans continued to expand. Plants and animals that survived the disaster of the Cretaceous period found themselves in a completely new world. Unique communities of life forms began to form on each continent.
The Cenozoic era is divided into three periods: Paleogene, Neogene and Quaternary.
1. Paleogene period ended approximately 23 million years ago. At this time, the earth reigned tropical climate, Europe was hidden under evergreen tropical forests, only deciduous trees grew in the north of the continents. It was during the Paleogene period that mammals developed rapidly.
2. Neogene period covers the next 20 million years of the planet's development. Whales and bats appear. And, although saber-toothed tigers and mastodons still roam the earth, the fauna is increasingly acquiring modern features.
3. Quaternary period began more than 2.5 million years ago and continues to this day. Two most important events characterize this time period: the ice age and the appearance of man. The Ice Age completely completed the formation of the climate, flora and fauna of the continents. And the appearance of man marked the beginning of civilization.