Chronological timeline. Geochronological scale
GEOCHRONOLOGICAL SCALE (relative geological time scale), a sequence of subordinate geochronological units of various ranks, arranged in chronological order and covering the entire geological history of the Earth. The basis of the geochronological scale was the general stratigraphic scale developed by many years of practice, mainly by European geologists in the 19th century, which is still being refined to this day. The time intervals during which sediments accumulated, taken as standards (stratotypes) of general stratigraphic units, were taken as general geochronological units. Geochronological divisions - akron, zone, era, period, epoch, century, phase - correspond to stratigraphic divisions - acrotheme, eonoteme, eratheme (group), system, department, stage, zone. The names of geochronological units indicate the relative geological age of objects of geological research.
Initially, the geochronological scale, combined with the stratigraphic scale, was compiled and approved at the 2nd session of the International Geological Congress in Bologna (Italy) in 1881 as a sequence of periods divided into epochs; Since then it has been constantly improved. In this scale, the history of the Earth was divided into four eras, based on the global stages of development of the organic world, in connection with which their names were proposed: Archean, or Archeozoic, - the era of ancient life; Paleozoic - era of ancient life; Mesozoic - era of middle life; Cenozoic - era of new life. In 1887, the Proterozoic era, the era of primary life, was separated from the Archean era. Later, it became necessary to distinguish divisions larger than eras - eons, which included the Archaean, Proterozoic and Phanerozoic (combining the Paleozoic, Mesozoic and Cenozoic eras).
In Russia, in the Precambrian part of the geochronological scale (1992), taking into account the enormous duration of the Precambrian (86% of the entire geological history), divisions of an even larger level were identified - the Acrons, to the rank of which the Archean and Proterozoic were elevated. At the beginning of the 21st century, the geochronological scale has the form presented in tables. There are 12 periods in the Phanerozoic eon: Cambrian, Ordovician, Silurian, Devonian, Carboniferous, Permian (comprising the Paleozoic era); Triassic, Jurassic, Cretaceous (Mesozoic era); Paleogene, Neogene and Quaternary (Cenozoic era). The names of the periods correspond to the names of the systems, which are mainly given by the name of the area where the systems were first identified and most fully described. Smaller divisions than periods on the geochronological scale are epochs, of which there are two (early and late) or three (early, middle and late). In some cases, eras have their own names (for example, the eras of the Paleogene and Neogene periods). The next, more detailed divisions of the geochronological scale are centuries and phases subordinate to them. All period boundaries and most of the epochs are dated by isotope methods.
Geochronological scale adopted in Russia, millions of years*
In Russia, the geochronological scale, combined with the General Stratigraphic Scale, was approved by the Interdepartmental Stratigraphic Committee (MSC) and included in the Stratigraphic Code (1992), additions to which were made in 2000. The international stratigraphic (geochronological) scale, developed by the International Commission on Stratigraphy and approved by the International Union of Geological Sciences (2004), in the Phanerozoic part differs from the domestic scale in the absence of the Quaternary period, which is included in the Neogene period, and a different division into epochs and centuries of the periods of the Paleozoic era; in the Precambrian part of the scale, acrons are not distinguished, and the Archean and Proterozoic are considered as divisions of a lower rank - eons, which have a different division into eras and periods than in the Russian geochronological scale.
Lit.: Stratigraphic Code. St. Petersburg, 1992; Additions to the Stratigraphic Code of Russia. St. Petersburg, 2000; And geological time scale // Ed. by F. M. Gradstein, J. G. Ogy, A. G. Smith. 3rd ed. Camb.; N.Y., 2004.
is the totality of all forms of the earth's surface. They can be horizontal, inclined, convex, concave, complex.
The difference in altitude between the highest peak on land, Mount Qomolungma in the Himalayas (8848 m), and the Mariana Trench in the Pacific Ocean (11,022 m) is 19,870 m.
How was the topography of our planet formed? In the history of the Earth, there are two main stages of its formation:
- planetary(5.5-5.0 million years ago), which ended with the formation of the planet, the formation of the Earth’s core and mantle;
- geological, which began 4.5 million years ago and continues to this day. It was at this stage that the formation of the earth's crust occurred.
The source of information about the development of the Earth during the geological stage is primarily sedimentary rocks, which in the vast majority were formed in an aquatic environment and therefore lie in layers. The deeper the layer lies from the earth’s surface, the earlier it was formed and, therefore, is more ancient in relation to any layer that is located closer to the surface and is younger. The concept is based on this simple reasoning relative age of rocks, which formed the basis for the construction geochronological table(Table 1).
The longest time intervals in geochronology are zones(from Greek aion - century, era). The following zones are distinguished: cryptozoic(from Greek cryptos - hidden and zoe- life), covering the entire Precambrian, in the sediments of which there are no remains of skeletal fauna; Phanerozoic(from Greek phaneros - obvious, zoe - life) - from the beginning of the Cambrian to the present time, with rich organic life, including skeletal fauna. The zones are not equivalent in duration; for example, if the Cryptozoic lasted 3-5 billion years, then the Phanerozoic lasted 0.57 billion years.
Table 1. Geochronological table
|
Era. letter designation, duration |
The main stages of life development |
Periods, letter designation, duration |
Major geological events. The appearance of the earth's surface |
Most common minerals |
|
Cenozoic, KZ, about 70 million years |
The dominance of angiosperms. The flourishing of the mammal fauna. The existence of natural zones close to modern ones, with repeated shifts of boundaries |
Quaternary, or anthropogenic, Q, 2 million years |
General rise of the territory. Repeated glaciations. The emergence of man |
Peat. Placer deposits of gold, diamonds, precious stones |
|
Neogene, N, 25 Ma |
The emergence of young mountains in areas of Cenozoic folding. Revival of mountains in areas of all ancient folds. Dominance of angiosperms (flowering plants) |
Brown coals, oil, amber |
||
|
Paleogene, P, 41 Ma |
Destruction of the Mesozoic mountains. Widespread distribution of flowering plants, development of birds and mammals |
Phosphorites, brown coals, bauxites |
||
|
Mesozoic, MZ, 165 Ma |
Melova, K, 70 million years |
The emergence of young mountains in areas of Mesozoic folding. Extinction of giant reptiles. Development of birds and mammals |
Oil, oil shale, chalk, coal, phosphorites |
|
|
Jurassic, J, 50 Ma |
Formation of modern oceans. Hot, humid climate. The heyday of reptiles. Dominance of gymnosperms. The emergence of primitive birds |
Hard coals, oil, phosphorites |
||
|
Triassic, T, 45 Ma |
The greatest retreat of the sea and the rise of continents in the entire history of the Earth. Destruction of pre-Mesozoic mountains. Vast deserts. First mammals |
Rock salts |
||
|
Paleozoic, PZ, 330 Ma |
The blossoming of ferns and other spore-bearing plants. Time of fish and amphibians |
Permian, R, 45 Ma |
The emergence of young mountains in the areas of the Hercynian fold. Dry climate. The emergence of gymnosperms |
Rock and potassium salts, gypsum |
|
Carboniferous (Carboniferous), C, 65 Ma |
Widespread lowland swamps. Hot, humid climate. Development of forests of tree ferns, horsetails and mosses. The first reptiles. The rise of amphibians |
Abundance of coal and oil |
||
|
Devonian, D, 55 million lei |
Reducing the size of the seas. Hot climate. The first deserts. The appearance of amphibians. Numerous fish |
Salts, oil |
||
|
The appearance of animals and plants on Earth |
Silurian, S, 35 Ma |
The emergence of young mountains in the areas of the Caledonian fold. First land plants |
||
|
Ordovician, O, 60 Ma |
Reducing the area of sea basins. The appearance of the first terrestrial invertebrates |
|||
|
Cambrian, E, 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, PR. about 2000 million years |
The origin of life in water. Time for bacteria and algae |
The beginning of the Baikal folding. Powerful volcanism. Time for bacteria and algae |
Huge reserves of iron ores, mica, graphite |
|
|
Archean, AR. more than 1000 million years |
The oldest folds. Intense volcanic activity. Time of primitive bacteria |
Iron ores |
Zones are divided into era. In cryptozoic they distinguish Archean(from Greek archaios- primordial, ancient, aion - century, epoch) and Proterozoic(from Greek proteros - earlier, zoe - life) era; in the Phanerozoic - Paleozoic(from Greek ancient and life), Mesozoic(from Greek tesos - middle, zoe - life) and Cenozoic(from Greek kainos - new, zoe - life).
Eras are divided into shorter periods of time - periods, established only for the Phanerozoic (see Table 1).
Main stages of development of the geographical envelope
The geographical envelope has gone through a long and difficult path of development. In all development, three qualitatively different stages are distinguished: prebiogenic, biogenic, anthropogenic.
Prebiogenic stage(4 billion - 570 million years) - the longest period. At this time, there was a process of increasing the thickness and complication of the composition of the earth's crust. By the end of the Archean (2.6 billion years ago), continental crust with a thickness of about 30 km had already formed over vast areas, and in the early Proterozoic the separation of protoplatforms and protogeosynclines occurred. During this period, the hydrosphere already existed, but the volume of water in it was less than now. Of the oceans (and only towards the end of the Early Proterozoic) one took shape. The water in it was salty and the salinity level was most likely about the same as it is now. But, apparently, in the waters of the ancient ocean the predominance of sodium over potassium was even greater than now; there were also more magnesium ions, which is associated with the composition of the primary earth's crust, the weathering products of which were carried into the ocean.
The Earth's atmosphere at this stage of development contained very little oxygen, and there was no ozone shield.
Life most likely existed from the very beginning of this stage. According to indirect data, microorganisms lived already 3.8-3.9 billion years ago. The discovered remains of simple organisms are 3.5-3.6 billion years old. However, organic life from the moment of its origin until the very end of the Proterozoic did not play a leading, determining role in the development of the geographical envelope. In addition, many scientists deny the presence of organic life on land at this stage.
The evolution of organic life into the prebiogenic stage was slow, but nevertheless, 650-570 million years ago, life in the oceans was quite rich.
Biogenic stage(570 million - 40 thousand years ago) lasted throughout the Paleozoic, Mesozoic and almost the entire Cenozoic, with the exception of the last 40 thousand years.
The evolution of living organisms during the biogenic stage was not smooth: eras of relatively calm evolution were replaced by periods of rapid and profound transformations, during which some forms of flora and fauna became extinct and others became widespread.
Simultaneously with the appearance of terrestrial living organisms, soils as we know them today began to form.
Anthropogenic stage began 40 thousand years ago and continues today. Although man as a biological species appeared 2-3 million years ago, his impact on nature remained extremely limited for a long time. With the advent of Homo sapiens, this impact increased significantly. This happened 38-40 thousand years ago. This is where the anthropogenic stage in the development of the geographic envelope begins.
Q
The geochronological scale is represented by the sequence of the history of the Earth, dividing it into a system of time intervals. It reflects the relative age of layers of sedimentary rocks, determined on the basis of their relative positions and the presence of organic remains.
History of creation
The geochronological scale was compiled and approved in 1881 at the International Geological Congress. Initially, it was a sequence of periods divided into eras. The latter were united into eras. That is, the original scale included three divisions. Later, a fourth, larger category was introduced - aeon. In 2004, the International Union of Geological Sciences approved the model developed by the International Commission on Stratigraphy.
In Russia, the geochronological scale, combined with the stratigraphic one, was approved at the end of the 20th century. (1992). At the same time, they added an even larger division - Acrons.
Basic principles
The geochronological scale is based on the division of sedimentary rocks or associated igneous massifs by relative age.
Its definition relates to the tasks of geochronology. For this purpose, methods of paleontology and stratigraphy are used.
Application
The use of the geochronological scale is determined by the fact that it connects geological events in the history of the planet. In view of this, it is widely used in the sciences of the geological cycle. In addition, the stratigraphic scale is the basis for drawing up geological maps.
In addition, the geochronological scale is of great practical importance. Thus, it is used in regional geological studies aimed at elucidating the tectonic features of the territory, determining the direction of searches and exploration of minerals, especially those confined to strata deposits corresponding to specific stratigraphic levels. Geological maps created on the basis of the geochronological scale are used when carrying out geotechnical work, environmental studies, etc.
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And finally, scientists had to solve one more problem: how did modern continents take their current places? The theory of continental drift answered this question. At first it was expressed as a bold assumption, then it became a hypothesis, and today, on its basis, the theory of lithospheric plate tectonics has been developed - the fundamental concept of modern geology. Thanks to it, we know about the movement of continents, how continental plates move and collide with each other, oceans appear and disappear again, and we also understand that earthquakes, volcanic eruptions, “hot zones” of the earth’s crust and mountain building are manifestations of one and the same the same process - tectonics. This theory helped test many previously existing ideas about the emergence and subsequent changes of the atmosphere, oceans, the Earth itself and life on it.
One of the main tasks of geological research is determining the age of the rocks that make up the earth's crust. There are relative and absolute ages. There are several methods for determining the relative age of rocks: stratigraphic and paleontological.
The stratigraphic method is based on the analysis of sedimentary rocks (marine and continental) and determination of the sequence of their formation. The layers below are older, those above are younger. This method establishes the relative age of rocks in a certain geological section in small areas.
The paleontological method consists of studying the fossilized remains of the organic world. The organic world has undergone significant changes in the course of geological history. The study of sedimentary rocks in a vertical section of the earth's crust showed that a certain complex of layers corresponds to a certain complex of plant and animal organisms.
Thus, plant and animal fossils can be used to determine the age of rocks. Fossils are the remains of extinct plants and animals, as well as traces of their vital activity. To determine the geological age, not all organisms are important, but only the so-called leading ones, that is, those organisms that, in the geological sense, did not exist for long.
Leading fossils must have a small vertical distribution, a wide horizontal distribution, and be well preserved. In each geological period, a certain group of animals and plants developed. Their fossilized remains are found in sediments of the corresponding age. In ancient layers of the earth's crust, remains of primitive organisms are found, in younger ones, highly organized ones. The development of the organic world occurred in an ascending line; from simple to complex organisms. The closer to our time, the greater the similarity with the modern organic world. The paleontological method is the most accurate and widely used.
Table composition
The geochronological scale was created to determine the relative geological age of rocks. Absolute age, measured in years, is of secondary importance to geologists. The existence of the Earth is divided into two main intervals: Phanerozoic and Precambrian (cryptozoic) according to the appearance of fossil remains in sedimentary rocks. Cryptozoic is a time of hidden life; only soft-bodied organisms existed in it, leaving no traces in sedimentary rocks. The Phanerozoic began with the appearance at the border of the Ediacaran (Vendian) and Cambrian of many species of mollusks and other organisms, allowing paleontology to subdivide the strata based on finds of fossil flora and fauna.
Another major division of the geochronological scale has its origins in the very first attempts to divide the history of the Earth into major time intervals. Then the whole history was divided into four periods: primary, which is equivalent to the Precambrian, secondary - the Paleozoic and Mesozoic, tertiary - the entire Cenozoic without the last Quaternary period. The Quaternary period occupies a special position. This is the shortest period, but many events took place in it, the traces of which are better preserved than others.
Based on stratigraphic and paleontological methods, a stratigraphic scale was constructed, presented in Fig. 1, in which the rocks that make up the earth's crust are located in a certain sequence in accordance with their relative age. This scale identifies groups, systems, departments, and tiers. Based on the stratigraphic scale, a geochronological table has been developed, in which the time of formation of groups, systems, divisions and stages is called an era, period, epoch, century.
Fig.1. Geochronological scale
The entire geological history of the Earth is divided into 5 eras: Archean, Proterozoic, Paleozoic, Mesozoic, Cenozoic. Each era is divided into periods, periods into eras, eras into centuries.
Features of determining the age of rocks
Absolute geological age is the time that has elapsed from any geological event to the modern era, calculated in absolute units of time (in billions, millions, thousands, etc. years). There are several methods for determining the absolute age of rocks.
The sedimentation method comes down to determining the amount of clastic material that is annually carried away from the surface of the land and deposited on the bottom of the sea. Knowing how much sediment accumulates on the seabed during the year and measuring the thickness of sedimentary strata accumulated in individual geological periods, one can find out the length of time required for the accumulation of these sediments.
The sedimentation method is not entirely accurate. Its inaccuracy is explained by the unevenness of sedimentation processes. The rate of sedimentation is not constant, it changes, intensifying and reaching a maximum during periods of tectonic activity of the earth's crust, when the earth's surface has highly dissected forms, due to which denudation processes intensify and, as a result, more sediment flows into marine basins. During periods of less active tectonic movements of the earth's crust, denudation processes weaken and the amount of precipitation decreases. This method gives only an approximate idea of the geological age of the Earth.
Radiological methods the most accurate methods for determining the absolute age of rocks. They are based on the use of radioactive decay of isotopes of uranium, radium, potassium and other radioactive elements. The rate of radioactive decay is constant and does not depend on external conditions. The end products of the decay of uranium are helium and lead Pb2O6. From 100 grams of uranium, 1 gram (1%) of lead is formed in 74 million years. If we determine the amount of lead (in percent) in the mass of uranium, then by multiplying by 74 million we get the age of the mineral, and from it the lifetime of the geological formation.
Recently, a radioactive method has been used, which is called potassium or argon. In this case, the potassium isotope with atomic weight 40 is used. The potassium method has the advantage that potassium is widely distributed in nature. As potassium decomposes, calcium and argon gas are formed. The disadvantage of the radiological method is the limited possibility of its use mainly for determining the age of igneous and metamorphic rocks.
Geochronological table- this is one way of representing the stages of development of planet Earth, in particular life on it. The table records eras, which are divided into periods, their age and duration are indicated, and the main aromorphoses of flora and fauna are described.
Often in geochronological tables, earlier, i.e., older, eras are recorded at the bottom, and later, i.e., younger, eras are recorded at the top. Below is data on the development of life on Earth in natural chronological order: from old to new. The tabular form has been omitted for convenience.
Archean era
It began approximately 3500 million (3.5 billion) years ago. Lasted about 1000 million years (1 billion).
In the Archean era, the first signs of life on Earth appeared - single-celled organisms.
According to modern estimates, the age of the Earth is more than 4 billion years. Before the Archean there was the Catarchean era, when there was no life yet.
Proterozoic era
It began approximately 2700 million (2.7 billion) years ago. Lasted for more than 2 billion years.
Proterozoic - the era of early life. Rare and scarce organic remains are found in the layers belonging to this era. However, they belong to all types of invertebrate animals. Also, the first chordates most likely appear - skullless.
Palaeozoic
It began about 570 million years ago and lasted more than 300 million years.
Paleozoic - ancient life. Starting with it, the process of evolution is better studied, since the remains of organisms from higher geological layers are more accessible. Hence, it is customary to examine each era in detail, noting changes in the organic world for each period (although both the Archean and the Proterozoic have their own periods).
Cambrian period (Cambrian)
Lasted about 70 million years. Marine invertebrates and algae thrive. Many new groups of organisms appear - the so-called Cambrian explosion occurs.
Ordovician period (Ordovician)
Lasted 60 million years. The heyday of trilobites and crustaceans. The first vascular plants appear.
Silurian (30 Ma)
- Coral blossom.
- The appearance of scutes - jawless vertebrates.
- The appearance of psilophyte plants coming onto land.
Devonian (60 Ma)
- The flourishing of the corymbs.
- Appearance of lobe-finned fishes and stegocephali.
- Distribution of higher spores on land.
Carboniferous period
Lasted about 70 million years.
- The rise of amphibians.
- The appearance of the first reptiles.
- The appearance of flying forms of arthropods.
- Decline in trilobite numbers.
- Fern blossoming.
- The appearance of seed ferns.
Perm (55 million)
- Distribution of reptiles, emergence of wild-toothed lizards.
- Extinction of trilobites.
- Disappearance of coal forests.
- Distribution of gymnosperms.
Mesozoic era
The era of middle life.
Geochronology and stratigraphy
It began 230 million years ago and lasted about 160 million years.
Triassic
Duration - 35 million years. The flourishing of reptiles, the appearance of the first mammals and true bony fish.
Jurassic period
Lasted about 60 million years.
- Dominance of reptiles and gymnosperms.
- The appearance of Archeopteryx.
- There are many cephalopods in the seas.
Cretaceous period (70 million years)
- The appearance of higher mammals and true birds.
- Wide distribution of bony fish.
- Reduction of ferns and gymnosperms.
- The emergence of angiosperms.
Cenozoic era
An era of new life. It began 67 million years ago and lasts the same amount.
Paleogene
Lasted about 40 million years.
- The appearance of tailed lemurs, tarsiers, parapithecus and dryopithecus.
- Rapid flourishing of insects.
- The extinction of large reptiles continues.
- Entire groups of cephalopods are disappearing.
- Dominance of angiosperms.
Neogene (about 23.5 million years)
Dominance of mammals and birds. The first representatives of the genus Homo appeared.
Anthropocene (1.5 Ma)
The emergence of the species Homo Sapiens. The animal and plant world takes on a modern appearance.
In 1881, at the II International Geological Congress in Bologna, the International Geochronological Scale was adopted, which is a broad systematic synthesis of the work of many generations of geologists in various fields of geological knowledge. The scale reflects the chronological sequence of time divisions during which certain complexes of sediments and the evolution of the organic world were formed, i.e. the international geochronological scale reflects the natural periodization of the history of the Earth. It is built on the principle of rank subordination of time and stratigraphic units from larger to smaller (Table 6.1). 
Each temporary division corresponds to a complex of sediments, distinguished in accordance with changes in the organic world and called a stratigraphic division.
Therefore, there are two scales: geochronological and stratigraphic (Tables 6.2, 6.3, 6.4). In these scales, the entire history of the Earth is divided into several eons and their corresponding eonotemes.
Geochronological and stratigraphic scales are constantly changing and improving. The scale given in table. 6.2, has an international rank, but it also has options: instead of the Carboniferous period on the European scale, in the USA there are two periods: the Mississippian, following the Devonian, and the Pennsylvanian, preceding the Permian.
Each era (period, epoch, etc.) is characterized by its own complex of living organisms, the evolution of which is one of the criteria for constructing a stratigraphic scale.
In 1992, the Interdepartmental Stratigraphic Committee published a modern stratigraphic (geochronological) scale, which is recommended for all geological organizations in our country (see Tables 6.2, 6.3, 6.4), but it is not generally accepted on a global scale; the greatest disagreements exist for the Precambrian and for the Quaternary system. 
Notes
Highlighted here:
1. Archean eon (AR) (ancient life), to which the stratigraphic mass of rocks corresponds - the Archean eonothem.
2. Proterozoic eon (PR) (primary life) - it corresponds to the stratigraphic strata of rocks - the Proterozoic eonothem.
3. Phanerozoic eon, divided into three eras:
3.1 - Paleozoic era (PZ) (era of ancient life) - it corresponds to the Paleozoic rock mass - Paleozoic erathema (group);
3.2 - Mesozoic era (MZ) (era of middle life) - it corresponds to the Mesozoic rock mass - Mesozoic erathema (group);
3.3 - Cenozoic era (KZ) (era of new life) - it corresponds to the Cenozoic rock formation - Cenozoic erathema (group).
The Archean eon is divided into two parts: the early (older than 3500 million years) and the late Archean. The Proterozoic eon is also divided into two parts: early and late Proterozoic; in the latter, the Riphean period (R) is distinguished (after the ancient name of the Urals - Ripheus) and the Vendian period (V) - after the name of the ancient Slavic tribe “Vedas” or “Vendas”.
The Phanerozoic eon and eonotema are divided into three eras (eratems) and 12 periods (systems). The names of the periods are usually assigned to the name of the area where they were first identified and most fully described.
In the Paleozoic era (erathema) are allocated accordingly.
1. Cambrian period (6) - Cambrian system (Є) - after the ancient name of the province of Wales in England - Cambria;
2. Ordovician period (O) - Ordovician system (O) - after the name of the ancient tribes of England that inhabited those areas - “Mordovians”;
3. Silurian period (S) - Silurian system (S) - after the name of the ancient tribes of England - “Silurians”;
4. Devonian period (D) - Devonian system (D) - after the name of the county of Devonshire in England;
5. Carboniferous (Carboniferous) period (C) - Carboniferous (Carboniferous) system (O - by the widespread development of coal deposits in these deposits;
6. Permian period (P) - Permian system (P) - after the name of the Perm province in Russia.
In the Mesozoic era (erathema) are allocated accordingly.
1. Triassic period (T) - Triassic system (T) - by dividing the period (system) into three parts;
2) Jurassic period (J) - Jurassic system (J) - named after the Jurassic Mountains in Switzerland;
3. Cretaceous period (K) - Cretaceous system (K) - according to the widespread development of writing chalk in the deposits of this system.
In the Cenozoic era (erathema) are allocated accordingly.
1. Paleogene period (P) - Paleogene system (P) - the most ancient part of the Cenozoic era;
2. Neogene period (N) - Neogene system (N) - newborns;
3. Quaternary period (Q) - Quaternary system (Q) - according to the proposal of academician.
Geochronological scale
A.A. Pavlova, sometimes called the Anthropocene.
Indices (symbols) of eras (erathems) are designated by the first two letters of Latin transcription, and periods (systems) by the first letter.
On geological maps and sections, for ease of depiction, each age system is assigned a specific color. Periods (systems) are divided accordingly into epochs (divisions). The duration of geological periods varies - from 20 to 100 million years. The exception is the Quaternary period - 1.8 million years, but it has not ended yet.
Early, middle, late eras correspond to the lower, middle, upper sections. There may be two or three eras (departments). The indices of eras (departments) correspond to the index of their periods (systems) with the addition of numbers at the bottom right - 1,2,3. For example, 5, is the Early Silurian era, and S2 is the Late Silurian era. To color designate eras (divisions), the color of their periods (systems) is used for earlier (later) - darker shades. The eras (divisions) of the Jurassic period and the Cenozoic era retained their own names. The stratigraphic and geochronological units of the Cenozoic era (groups) have their own names: P1 - Paleocene, P2 - Eocene, P3 - Oligocene, N1 - Miocene, N2 - Pliocene, QI, QII, QIII - epochs (divisions) early (lower), middle (mid-), late Quaternary (upper Quaternary) - together called the Pleistocene, and Q4 - Holocene.
The next and more fractional units of the geochronological and stratigraphic scales are centuries (stages) lasting from 2 to 10 million years. They are given geographical names.
1. Geological time scale
1.5. Geochronological and stratigraphic scales.
Irreversibility of time
3. Natural history of the Middle Ages
List of used literature
1. Geological time scale
Physical, cosmological, chemical concepts lead close to ideas about the Earth, its origin, structure and various properties. The complex of geosciences is usually called geology(Greek ge – Earth). Earth is a place and a necessary condition for the existence of humanity. For this reason, geological concepts are of the utmost importance to humans. We have to understand the nature of their evolution. Geological concepts do not arise spontaneously; they are the result of painstaking scientific research.
The Earth is a unique space object. The idea of the evolution of the Earth occupies a central place in his study. Taking this into account, let us turn, first of all, to such an important quantitative-evolutionary parameter of the Earth as its time, geological time.
The development of scientific concepts about geological time is complicated by the fact that the lifespan of a human individual is a tiny fraction of the age of the Earth (approx. 4.6 * 109 years). Simple extrapolation of current geological time into the depths of past geological time does not give anything. To obtain information about the geological past of the Earth, some special concepts are needed. There are a variety of ways to think about geological time, chief among them lithological, biostratigraphic, and radiological.
The lithological concept of geological time was first developed by the Danish physician and naturalist N. Stensen (Steno). According to the concept of Steno (1669), in a series of normally occurring strata, the overlying strata are younger than the underlying ones, and the cracks and mineral veins cutting them are even younger. Steno's main idea is this: the layered structure of the Earth's surface rocks is a spatial reflection of geological time, which, of course, also has a certain structure. In the development of Steno's ideas, geological time is determined by the accumulation of sediments in the seas and oceans, river sediments in the estuarine areas of the coast, by the height of dunes, and by the thicknesses of “ribbon” clays that appear at the edges of glaciers as a result of their melting.
In the biostratigraphic understanding of geological time, the remains of ancient organisms are taken into account: the fauna and flora lying higher are considered younger. This pattern was established by the Englishman W. Smith, who compiled the first geological map of England dividing rocks by age (1813-1815). It is important that, unlike lithological layers, biostratigraphic features extend over long distances and are present throughout the entire shell of the Earth as a whole.
Based on litho- and biostratigraphic data, attempts have been made repeatedly to create a unified (bio)stratigraphic scale of geological time. However, along this path, researchers have invariably encountered indefinable difficulties. Based on (bio)stratigraphic data, it is possible to determine the “older-younger” relationship, but it is difficult to determine how many years one layer formed before the other. But the task of ordering geological events requires the introduction of not only ordinal, but also quantitative (metric) characteristics of time.
In the radiological measurement of time, in the so-called isotope chronology, the age of geological objects is determined based on the ratio of the parent and daughter isotopes of the radioactive element in them. The idea of radiological time measurement was proposed at the beginning of the twentieth century. P. Curie and E. Rutherford.
Isotope geochronology has made it possible to use not only ordinal definitions of the “earlier-later” type in procedures for measuring geological time, but also quantitative definitions. In this regard, the geological time scale is introduced, which is usually presented in different versions. One of them is given below.
Intervals of geological time (beginnings of periods and epochs in millions of years from the present)
In the names of geological periods, only two expressions have been preserved from their early classification: Tertiary and Quaternary. Some of the names of geological periods are associated either with localities or with the nature of material deposits. So, Devonian The period characterizes the age of sediments first studied in Devonshire in England. Chalky The period characterizes the age characteristics of geological deposits containing a lot of chalk.
2. Irreversibility of time
Time – this is a form of existence of matter, expressing the order of change in objects and phenomena of reality. Characterizes the actual duration of actions, processes, events; denotes the interval between events.
Unlike space, to each point of which you can return again and again, time – irreversible And one-dimensionally. It flows from the past through the present to the future. You cannot go back to any point in time, but you cannot jump over any time period into the future. It follows that time constitutes, as it were, a framework for cause-and-effect relationships. Some argue that the irreversibility of time and its direction are determined by cause and connection, since the cause always precedes the effect. However, it is obvious that the concept of precedence already presupposes time. Therefore, G. Reichenbach is more correct when he writes: “Not only the temporal order, but also the unified space-time order is revealed as an ordering scheme governing causal chains, and thus as an expression of the causal structure of the universe.”
The irreversibility of time in macroscopic processes is embodied in the law of increasing entropy. In reversible processes, entropy remains constant, in irreversible processes it increases. Real processes are always irreversible. In a closed system, the maximum possible entropy corresponds to the onset of thermal equilibrium in it: temperature differences in individual parts of the system disappear and macroscopic processes become impossible. All the energy inherent in the system is converted into the energy of disordered, chaotic movement of microparticles, and the reverse transition of heat into work is impossible.
It turned out that time cannot be considered as something separately taken. And in any case, the measured value of time depends on the relative movement of the observers. Therefore, two observers moving relative to each other and watching two different events will come to different conclusions about how separated the events are in space and time. In 1907, the German mathematician Hermann Minkowski (1864-1909) suggested a close connection between three spatial and one temporal characteristics. In his opinion, all events in the Universe occur in a four-dimensional space-time continuum.
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