Geological scale

Geochronological scale - the geological time scale of the history of the Earth, used in geology and paleontology, a kind of calendar for time intervals of hundreds of thousands and millions of years.

According to modern generally accepted ideas, the age of the Earth is estimated at 4.5-5 billion years. In modern geology, the most common age estimate is 4.55-4.56 billion years, with an error estimate of several percent. Such estimates are based on the data of determining the age of rocks by radioisotope dating. The figure of 4.567 billion years is a kind of compromise between various datings of the age of rocks, which give figures from 4.2 to 4.6 billion years.

This time was divided into different time intervals according to the most important events that took place then.

The boundary between the Phanerozoic eras runs along the largest evolutionary events - global extinctions. The Paleozoic is separated from the Mesozoic by the largest Permian-Triassic extinction of species in the history of the Earth. The Mesozoic was separated from the Cenozoic by the Cretaceous-Paleogene extinction.

The history of the scale

In the second half of the 19th century, at the II-VIII sessions of the International Geological Congress (IGC) in 1881-1900. the hierarchy and nomenclature of most modern geochronological units were adopted. Subsequently, the International geochronological (stratigraphic) scale was constantly refined.

In geology, as in no other science, the sequence of establishing events, their chronology, based on the natural periodization of geological history, is important. Geological chronology, or geochronology, is based on elucidating the geological history of the most well-studied regions, such as those in Central and Eastern Europe. Based on broad generalizations, comparison of the geological history of various regions of the Earth, patterns of evolution of the organic world at the end of the last century, at the first International Geological Congresses, the International Geochronological Scale was developed and adopted, reflecting the sequence of time divisions during which certain sediment complexes were formed, and the evolution of the organic world . Thus, the international geochronological scale is a natural periodization of the history of the Earth.

Among the geochronological divisions are distinguished: eon, era, period, epoch, century, time. Each geochronological subdivision corresponds to a set of deposits, identified in accordance with the change in the organic world and called stratigraphic: eonoteme, group, system, department, stage, zone. Therefore, the group is a stratigraphic unit, and the corresponding temporal geochronological unit is represented by an era. Therefore, there are two scales: geochronological and stratigraphic. We use the first when we talk about relative time in the history of the Earth, and the second when we deal with sediments, since some geological events took place in every place on the globe at any time interval. Another thing is that the accumulation of precipitation was not ubiquitous.

At present, there are three largest stratigraphic divisions - eonotemes: Archean, Proterozoic and Phanerozoic, which correspond to zones of different duration in the geochronological scale. The Archean and Proterozoic eonotemes, covering almost 80% of the time of the Earth's existence, are distinguished in the Cryptozoic, since the skeletal fauna is completely absent in the Precambrian formations and the paleontological method is not applicable to their division. Therefore, the division of Precambrian formations is based primarily on general geological and radiometric data. The Phanerozoic eon covers only 570 million years, and the division of the corresponding eonoteme of deposits is based on a wide variety of numerous skeletal fauna. The Phanerozoic eonoteme is subdivided into three groups: Paleozoic, Mesozoic and Cenozoic, corresponding to major stages in the natural geological history of the Earth, the boundaries of which are marked by rather abrupt changes in the organic world.

The names of eonotems and groups come from the Greek words: "archeos" - the most ancient, most ancient; "proteros" - primary; "paleos" - ancient; "mesos" - medium; "kainos" - new. The word "cryptos" means hidden, and "phanerozoic" means explicit, transparent, since the skeletal fauna appeared. The word "zoi" comes from "zoikos" - life. Therefore, "Cenozoic era" means the era of new life, and so on. Groups are subdivided into systems, the deposits of which were formed during one period and are characterized only by families or genera of organisms characteristic of them, and if these are plants, then by genera and species. Systems have been identified in different regions and at different times since 1822. At present, 12 systems are distinguished, the names of most of which come from the places where they were first described. For example, the Jurassic system from the Jura Mountains in Switzerland, the Permian - from the Perm province in Russia, the Cretaceous - according to the most characteristic rocks - white writing chalk, etc. The Quaternary system is often called Anthropogenic, since it is in this age interval that a person appears. The systems are subdivided into two or three divisions, which correspond to the early, middle, and late eras. The departments, in turn, are divided into tiers, which are characterized by the presence of certain genera and species of fossil fauna. And, finally, the stages are subdivided into zones, which are the most fractional part of the international stratigraphic scale, which corresponds to time in the geochronological scale. The names of the stages are usually given according to the geographical names of the regions where this stage was distinguished; for example, Albanian, Bashkirian, Maastrichtian, etc. At the same time, the zone is designated by the most characteristic type of fossil fauna. The zone covers, as a rule, only a certain part of the region and is developed over a smaller area than the deposits of the stage.

The specific names of the periods were given according to various criteria. The most commonly used place names. So, the name of the Cambrian period comes from lat. Cambria - the name of Wales when it was part of the Roman Empire, Devonian - from the county of Devonshire in England, Permian - from the city of Perm, Jurassic - from the Yuram Mountains in Europe. In honor of the ancient tribes, the Vendian (Vends are the German name for the Slavic people of the Lusatian Serbs), Ordovician and Silurian (tribes of the Celts Ordomviks and Silurs) periods are named. Names associated with the composition of the rocks were used less frequently. The Carboniferous period is named because of the large number of coal seams, and the Cretaceous because of the widespread use of writing chalk.

earth structure sun geochronological

is the totality of all forms of the earth's surface. They can be horizontal, inclined, convex, concave, complex.

The height difference between the highest peak on land, Mount Chomolungma in the Himalayas (8848 m), and the Mariana Trench in the Pacific Ocean (11,022 m) is 19,870 m.

How was the relief of our planet formed? In the history of the Earth, two main stages of its formation are distinguished:

planetary(5.5-5.0 million years ago), which ended with the formation of the planet, the formation of the core and mantle of the Earth;
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 the aquatic environment and therefore occur in layers. The deeper the layer lies from the earth's surface, the earlier it was formed and, therefore, is more ancient with respect to any layer that is closer to the surface and is younger. This simple reasoning is based on the concept 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, epoch). There are such zones as: cryptozoic(from Greek. cryptos- hidden and zoe- life), covering the entire Precambrian, in the deposits of which there are no remains of skeletal fauna; phanerozoic(from Greek. phaneros- explicit, zoe- life) - from the beginning of the Cambrian to our time, with a rich organic life, including skeletal fauna. The zones are not equal in duration, so if the Cryptozoic lasted 3-5 billion years, then the Phanerozoic lasted 0.57 billion years.

Table 1. Geological table

Era. letter designation, duration	The main stages of the development of life	Periods, letter designation, duration	major geological events. The shape of the earth's surface	Most Common Minerals
Cenozoic, KZ, about 70 Ma	dominance of angiosperms. The rise of the mammalian fauna. The existence of natural zones close to modern ones, with repeated displacements of boundaries	Quaternary, or Anthropogenic, Q, 2 million years	General uplift of the territory. repeated glaciations. The appearance of man	Peat. Alluvial deposits of gold, diamonds, precious stones
		Neogene, N, 25 Ma	The emergence of young mountains in the areas of Cenozoic folding. The revival of mountains in the regions of all ancient foldings. Dominance of angiosperms (flowering) plants	Brown coals, oil, amber
		Paleogene, P, 41 Ma	Destruction of the Mesozoic mountains. Wide distribution of flowering plants, development of birds and mammals	Phosphorites, brown coals, bauxites
Mesozoic, MZ, 165 Ma		Cretaceous, K, 70 Ma	The emergence of young mountains in the areas of Mesozoic folding. Extinction of giant reptiles (reptiles). Development of birds and mammals	Oil, oil shale, chalk, coal, phosphorites
Mesozoic, MZ, 165 Ma		Jurassic, J, 50 Ma	Formation of modern oceans. Hot, humid climate. The rise of reptiles. dominance of gymnosperms. Appearance of primitive birds	Coals, oil, phosphorites
		Triassic, T, 45 Ma	The greatest retreat of the sea and the rise of the continents in the entire history of the Earth. Destruction of pre-Mesozoic mountains. Vast deserts. First mammals	rock salts
Paleozoic, PZ, 330 Ma	The flowering of ferns and other spore plants. Time for fish and amphibians	Permian, R, 45 Ma	The emergence of young mountains in areas of Hercynian folding. Dry climate. The emergence of gymnosperms	Rock and potash salts, gypsum
		Carboniferous (Carboniferous), C, 65 Ma	Widespread swampy lowlands. Hot, humid climate. Development of forests from tree ferns, horsetails and club mosses. The first reptiles The heyday of amphibians	Abundance of coal and oil
		Devonian, D, 55 million years	Reduction of the seas. Hot climate. First deserts. The appearance of amphibians. Numerous fish	Salt, oil
	The appearance of animals and plants on Earth	Silurian, S, 35 Ma	The emergence of young mountains in the areas of the Caledonian folding. The first land plants
		Ordovician, O, 60 Ma	Decrease in the area of marine basins. Appearance of the first terrestrial invertebrates
		Cambrian, E, 70 Ma	The emergence of young mountains in the areas of Baikal folding. Flooding of vast areas by the seas. The rise of marine invertebrates	Rock salt, gypsum, phosphate rock
Proterozoic, PR. about 2000 Ma	Origin of life in water. Bacteria and algae time		Beginning of the Baikal folding. Powerful volcanism. Bacteria and algae time	Huge reserves of iron ores, mica, graphite
Archean, AR. over 1000 million years			Ancient folding. Intense volcanic activity. Time of primitive bacteria	Iron ores

The zones are divided into era. In the cryptozoic, there are Archean(from Greek. archaios- primordial, ancient aion- century, era) 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).

The main stages in the development of the geographical envelope

The geographical envelope has come a long and difficult path of development. There are three qualitatively different stages in its development: pre-biogenic, biogenic, and anthropogenic.

pre-biogenic stage(4 billion - 570 million years) - the longest period. At this time, the process of increasing the thickness and complicating the composition of the earth's crust took place. By the end of the Archean (2.6 billion years ago), a continental crust about 30 km thick had already formed over vast expanses, and in the Early Proterozoic, protoplatforms and protogeosynclines separated. During this period, the hydrosphere already existed, but the volume of water in it was less than now. Of the oceans (and then only by the end of the early Proterozoic) one took shape. The water in it was salty and the salinity level most likely was about the same as 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 screen.

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 the simplest organisms are 3.5-3.6 billion years old. However, organic life from the moment of its inception to 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 to the pre-biogenic stage proceeded slowly, but nevertheless, 650-570 million years ago, life in the oceans was quite rich.

Biogenic stage(570 million - 40 thousand years) lasted during 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 died out and others became widespread.

Simultaneously with the appearance of terrestrial living organisms, soils began to form in our modern understanding.

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 for a long time remained extremely limited. With the advent of Homo sapiens, this impact has increased significantly. It happened 38-40 thousand years ago. From here the anthropogenic stage in the development of the geographic envelope takes its countdown.

One of the main tasks of geological research is to determine the age of the rocks that make up the earth's crust. There are relative and absolute age. 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 determining the sequence of their formation. Layers lying at the bottom are older, at the top are younger. This method establishes the relative age of rocks in a certain geological section in small areas.

The paleontological method is the study of 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 has shown 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 life. For determining the geological age, not all organisms are important, but only the so-called guiding organisms, that is, those organisms that, in the geological understanding, did not exist for long.

Guide fossils should have a small vertical and 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 deposits of the corresponding age. In the ancient layers of the earth's crust, the remains of primitive organisms are found, in younger highly organized ones. The development of the organic world took place along 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 time of 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 - the time of hidden life, only soft-bodied organisms existed in it, leaving no traces in sedimentary rocks. The Phanerozoic began with the appearance on the border of the Ediacaran (Vendian) and Cambrian of many species of mollusks and other organisms, allowing paleontology to dissect the strata according to the finds of fossil flora and fauna.

Another major division of the geochronological scale has its origin 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: the primary, which is equivalent to the Precambrian, the secondary - the Paleozoic and Mesozoic, the 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.

On the basis of stratigraphic and paleontological methods, a stratigraphic scale has been constructed, shown in Fig. 1, in which the rocks that make up the earth's crust are arranged in a certain sequence in accordance with their relative age. Groups, systems, departments, tiers are distinguished in this scale. 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. Geological 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 - the time that has elapsed from any geological event to the present 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 is reduced to determining the amount of detrital material annually removed from the land surface and deposited on the seabed. Knowing how much precipitation accumulates on the seabed during the year and measuring the thickness of the sedimentary strata accumulated in certain 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 uneven processes of sedimentation. 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 strongly dissected forms, due to which denudation processes intensify and, as a result, more precipitation enters the sea 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 a rough 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 the 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 uranium decay are helium and lead Pb206. From 100 grams of uranium, 1 gram (1%) of lead is formed in 74 million years. If you determine the amount of lead (in percent) in the mass of uranium, then by multiplying by 74 million, you get the age of the mineral, and from it the time of existence of the geological layer.

Recently, they began to use the radioactive method, which was called potassium or argon. In this case, a potassium isotope with an atomic weight of 40 is used. The potassium method has the advantage that potassium is widely distributed in nature. During the decomposition of potassium, calcium and argon gas are formed. The disadvantage of the radiological method is the limited possibility of its application mainly for determining the age of igneous and metamorphic rocks.

Geological table- this is one of the ways to represent the stages of development of the planet Earth, in particular life on it. The table records eras, which are subdivided into periods, their age, duration are indicated, the main aromorphoses of flora and fauna are described.

Often in geochronological tables, earlier, i.e. older, eras are written at the bottom, and later, i.e., younger ones, at the top. Below are data on the development of life on Earth in natural chronological order: from oldest to newest. Tabular form omitted for convenience.

Archean era

It began about 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 appear - single-celled organisms.

According to modern estimates, the age of the Earth is more than 4 billion years. Before the Archean, there was the Catharchean era, when there was no life yet.

Proterozoic era

It began about 2700 million (2.7 billion) years ago. It lasted more than 2 billion years.

Proterozoic - the era of early life. In the layers belonging to this era, rare and few organic remains are found. However, they belong to all types of invertebrates. It is also likely that the first chordates appear - non-cranial.

Palaeozoic

It began about 570 million years ago and lasted more than 300 million years.

Paleozoic - ancient life. Starting from it, the process of evolution is better studied, since the remains of organisms from the upper geological layers are more accessible. Hence, it is customary to consider each era in detail, noting the changes in the organic world for each period (although their periods are distinguished both in the Archean and in the Proterozoic).

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, racoscorpions. The first vascular plants appear.

Silurian (30 Ma)

Bloom of corals.
The appearance of scutellum - jawless vertebrates.
The appearance of psilophyte plants that have come to land.

Devonian (60 Ma)

The flowering of corymbs.
The appearance of lobe-finned fish and stegocephalians.
Distribution on land of higher spores.

Carboniferous period

Lasted about 70 million years.

The rise of amphibians.
Appearance of the first reptiles.
The emergence of flying forms of arthropods.
Decline in the number of trilobites.
Blossoming ferns.
The emergence of seed ferns.

Perm (55 million)

The spread of reptiles, the emergence of animal-toothed lizards.
Trilobite extinction.
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 flowering of reptiles, the appearance of the first mammals and true bony fish.

Jurassic period

Lasted about 60 million years.

Dominance of reptiles and gymnosperms.
Appearance of Archeopteryx.
There are many cephalopods in the seas.

Cretaceous period (70 million years)

The emergence of higher mammals and true birds.
Widespread distribution of bony fish.
Reduction of ferns and gymnosperms.
The emergence of angiosperms.

Cenozoic era

The era of new life. It began 67 million years ago, lasts, respectively, the same amount.

Paleogene

Lasted about 40 million years.

Appearance of tailed lemurs, tarsiers, parapithecus and dryopithecus.
An explosion of insects.
The extinction of large reptiles continues.
Entire groups of cephalopods are disappearing.
dominance of angiosperms.

Neogene (about 23.5 Ma)

dominance of mammals and birds. The first representatives of the genus Homo appeared.

Anthropogene (1.5 Ma)

Appearance of Homo sapiens species. The animal and plant world takes on a modern look.

In 1881, at the II International Geological Congress in Bologna, the International Geochronological Scale was adopted, which is a broad systemic generalization 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 sediment complexes and the evolution of the organic world were formed, that is, the natural periodization of the Earth's history is reflected in the international geochronological scale. It is built on the principle of rank subordination of time and stratigraphic units from larger to smaller (Table 6.1).

Each temporal subdivision corresponds to a set of deposits, identified in accordance with the change in the organic world and called a stratigraphic subdivision.

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 corresponding eonotems.

Geochronological and stratigraphic scales are constantly changing and improving. The scale given in table. 6.2, has the rank of international, but it also has options: instead of the Carboniferous period in the European scale, two periods are distinguished in the USA: the Mississippian, following the Devonian, and the Pennsylvanian, preceding the Permian.

Each era (period, epoch, etc.) has 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) (earliest life), which corresponds to the stratigraphic thickness of rocks - the Archean eonoteme.

2. Proterozoic eon (PR) (primary life) - it corresponds to the stratigraphic stratum of rocks - the Proterozoic eonoteme.

3. Phanerozoic eon, subdivided into three eras:

3.1 - Paleozoic era (PZ) (era of ancient life) - it corresponds to the Paleozoic rock stratum - Paleozoic erathema (group);

3.2 - Mesozoic era (MZ) (era of middle life) - it corresponds to the Mesozoic rock stratum - Mesozoic erathema (group);

3.3 - Cenozoic era (KZ) (era of new life) - it corresponds to the Cenozoic rock strata - Cenozoic erathema (group).

The Archean eon is divided into two parts: early (older than 3500 Ma) and late Archean. The Proterozoic eon is also divided into two parts: early and late Proterozoic; in the latter, the Riphean (R) stands out (after the ancient name of the Urals - Ripheus) and the Vendian period (V) - after the name of the ancient Slavic tribe "Vedas" or "Venedi".

The Phanerozoic eon and eonoteme are subdivided into three eras (erathems) and 12 periods (systems). The name of the periods is usually assigned by the name of the area where they were first identified and most fully described.

In the Paleozoic era (eratem) are highlighted accordingly.

1. Cambrian period (6) - Cambrian system (Є) - according to the ancient name of the province of Wales in England - Cambria;

2. Ordovician period (O) - Ordovician system (O) - by the name of the ancient tribes of England that inhabited those areas - "Mordovicians";

3. Silurian period (S) - Silurian system (S) - by the name of the ancient tribes of England - "Silurs";

4. Devonian period (D) - Devonian system (D) - by the name of the county of Devonshire in England;

5. Carboniferous (Carboniferous) period (C) - Carboniferous (Carboniferous) system (O - by the wide development of coal deposits in these deposits;

6. Permian period (P) - Permian system (P) - by the name of the Permian province in Russia.

In the Mesozoic era (eratem) are highlighted accordingly.

1. Triassic period (T) - Triassic system (T) - by dividing the period (system) into three parts;

2) Jurassic period (J) - Jurassic system (J) - by the name of the Jura Mountains in Switzerland;

3. Cretaceous period (K) - Cretaceous system (K) - according to the wide development of writing chalk in the deposits of this system.

In the Cenozoic era (eratem) are highlighted 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) - at the suggestion of Acad.

Geological scale

A.A. Pavlova, sometimes called an anthropogen.

Indexes (symbols) of eras (erathems) are indicated by the first two letters of Latin transcription, and periods (systems) - by the first letter.

On geological maps and sections, for the convenience of depicting each age system, a specific color is assigned. Periods (systems) are divided into epochs (departments) respectively. The duration of geological periods is not the same - 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. Epochs (departments) can be two or three. The indices of epochs (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 epoch, and S2 is the late Silurian epoch. For the color designation of epochs (departments), the color of their periods (systems) is used for earlier (later) - darker shades. The epochs (departments) of the Jurassic period and the Cenozoic era retained their own names. 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 (departments) early (lower), medium (medium), late Quaternary (Upper Quaternary) - together they are called the Pleistocene, and Q4 - the Holocene.

The next and more fractional units of the geochronological and stratigraphic scales are the century (stage) with a duration of 2 to 10 Ma. They are named geographically.

1. Geological time scale

1.5. Geochronological and stratigraphic scales.

The irreversibility of time

3. Natural science 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 geoscience complex is commonly referred to as geology(Greek ge - Earth). Earth is a place and a necessary condition for the existence of mankind. For this reason, geological concepts are of the utmost importance to man. 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. Central to his study is the idea of the evolution of the earth. With this in mind, let us first of all turn to such an important quantitative and 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 lifetime of a human individual is an insignificant fraction of the age of the Earth (approx. 4.6 * 109 years). A simple extrapolation of the actual geological time into the depths of the past geological time does not give anything. To get information about the geological past of the Earth, some special concepts are needed. There are a variety of ways to comprehend geological time, the main ones being lithological, biostratigraphic and radiological.

The lithological concept of geological time was first developed by the Danish physician and naturalist N. Stensen (Steno). According to Steno's concept (1669), in a series of normally occurring strata, the overlying strata are younger than the underlying ones, and the fractures and mineral veins that cross them are even younger. Steno's main idea is this: the layered structure of the rocks on the Earth's surface is a spatial representation 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 sections of the coast, by the height of dunes, by the thickness 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 that lie higher are considered younger. This pattern was established by the Englishman W. Smith, who compiled the first geological map of England with the division of rocks according to their age (1813-1815). It is important that, in contrast to lithological layers, biostratigraphic features extend over long distances and are present throughout the entire shell of the Earth as a whole.

On the basis of litho- and biostratigraphic data, attempts have been repeatedly made to create a unified (bio)stratigraphic scale of geological time. However, along the way, researchers invariably ran into indefinable difficulties. From (bio)stratigraphic data it is possible to determine the older-younger relationship, but it is difficult to determine by how many years one layer was 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 radiological time measurement, in the so-called isotopic chronology, the age of geological objects is determined based on the ratio of the parent and daughter isotopes of a radioactive element in them. The idea of radiological time measurement was proposed at the beginning of the 20th century. P. Curie and E. Rutherford.

Isotopic geochronology made it possible to use not only ordinal definitions of the “earlier-later” type, but also quantitative definitions in the procedures for measuring geological time. In this regard, a geological time scale is introduced, which is usually presented in various versions. One of them is shown below.

Geological time intervals (beginnings of periods and epochs in millions of years from present)

In the names of geological periods from their early classification, only two expressions have been preserved: 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 deposits first studied in Devonshire, England. Chalky period characterizes the age features 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, where you can return to every point again and again, time - irreversibly 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 through any time interval into the future. It follows that time is, as it were, a framework for cause-and-effect relationships. Some argue that the irreversibility of time and its direction are determined by the cause by the connection, since the cause always precedes the effect. It is clear, however, that the notion of antecedence already presupposes time. More right, therefore, G. Reichenbach, who writes: "Not only the temporal order, but also the unified space-time order is revealed as an ordering scheme that controls 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 entropy increase. 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 motion of microparticles, and the reverse transition of heat into work is impossible.

It turned out that time cannot be considered as something taken separately. And in any case, the measured value of time depends on the relative motion of the observers. Therefore, two observers moving relative to each other and following two different events will come to different conclusions about how separated these events are in space and time. In 1907, the German mathematician Hermann Minkowski (1864-1909) suggested a close relationship between three spatial and one temporal characteristics. In his opinion, all events in the Universe occur in a four-dimensional space-time continuum.

The evolution of living beings can only be understood in the context of geological time.

Geochronological (stratigraphic) timeline - this is a scale of relative geological time, built on the basis of the stages of formation of the earth's crust and life on the planet, determined by paleontology and historical geology. It is a sequence of stratigraphic elements in the order of their formation, in the form of a complete composite ideal section of all terrestrial deposits without gaps and overlaps, and is a standard for the correlation of any stratigraphic units. The boundaries between stratigraphic elements are drawn by events of marked evolutionary or geological change. The doctrine of the chronological sequence of formation and age of the rocks that make up the earth's crust is called geochronology .

Distinguish between relative and absolute geochronology.

task relative geochronology is the determination of the relative age of rocks: determining which deposits found in the earth's crust are older and which are younger. There are several methods for determining the relative age of rocks.

First method - stratigraphic. He proceeds from a completely unclear and logical notion that each layer of sedimentary rocks was formed before the layer that overlies it.

Second method - paleontological. It allows you to establish the relative age of rocks and compare them in geological sections belonging to different areas or regions. Establishment is made according to the nature of various organic remains found in the layers (petrified sea shells, animal bones, leaf prints, etc.).

task absolute geochronology is to determine the true duration of individual periods and epochs in the life of the Earth, as well as its geological age as a whole.

The geochronological age of rocks is determined by units such as era, period, epoch, and century.

Era - the largest stage in the history of the development of the Earth, in which a group of deposits was formed. There are five eras (starting from the more ancient ones): Archean, Proterozoic, Paleozoic, Mesozoic and Cenozoic.

Each era covers several periods. The period corresponds to the time of formation of the rock system. The periods are subdivided into several epochs, which correspond to rock divisions. Epochs are subdivided into centuries, which correspond to tiers as a set of rocks formed in a particular century.

Archean(era of primary life) and Proterozoic(era of ancient life) era farthest from us in time (about 1.5 billion years). At this time, the most ancient rocks were formed that make up the rigid foundation of the earth's crust. The rocks of the Archean era bear only traces of primitive organic forms, testifying to the origin of life on Earth at this time. The Proterozoic era coincides in time with the beginning of the development of various algae, bacteria and invertebrates on Earth.

Palaeozoic(era of ancient life) - a period of time removed from us by about 600 million years and lasting about 350 million years. This era and the breeds related to it have been studied in more detail. The Paleozoic era is characterized by the flourishing of organic life in the seas and oceans and its emergence on land. On land, large amphibians become dominant, and at the end of the era, the first reptiles. In the Carboniferous period of the era, tree-like ferns, horsetails, etc.

The Paleozoic era is divided into six periods (starting from the more ancient ones): Cambrian (Cm), Ordovician (O), Silurian (S), Devonian (D), Carboniferous (C) and Permian (P).

Mesozoic era(the era of average life) lasting 185 million years is the heyday of giant reptiles on land (giant lizards - dinosaurs, flying pterodactyls, etc.). The flora and insect world in the Mesozoic have some features in common with our time. At this time, the first representatives of mammals and birds appeared on Earth, which developed in the next, Cenozoic era.

The Mesozoic era is divided into three periods: Triassic (T), Jurassic (J) and Cretaceous (Cr).

Cenozoic era(era of new life) - the youngest (about 40 ... 50 million years BC), which replaced the Mesozoic era. Life at this time takes on forms that are closer and closer to our time.

The Cenozoic era is divided into three periods: Paleogene (Pg), Neogene (N) and Anthropogenic (Ap), or Quaternary (Q). The Quaternary period is the last period in the development of the organic world, during which man appeared.

Rocks up to the Quaternary age are called indigenous, and the continental Quaternary age - coverslips. Within bedrocks, in general, older rocks are more durable than younger ones, while Quaternary cover formations are less durable than bedrocks. But there is no direct connection between the age of rocks and their strength, and sometimes young rocks are more durable than ancient ones.

As a result of studying the age, composition, conditions of occurrence and distribution of rocks, geological maps are compiled that show the outcrops of bedrocks on the surface of the earth. Deposits of the Quaternary time on geological maps, as a rule, do not show; for them, special maps of Quaternary (cover) deposits are compiled. They do this for the reason that the rocks until the Quaternary in the vast majority of cases are of marine origin and are distinguished by a well-identified regularity in the structure of the layers, both in plan and in depth. The rocks of the Quaternary age, on the contrary, in most cases are of continental origin (formed within the land). These rocks are characterized by an extremely variable composition, and the boundaries of their distribution are usually determined by the existing terrain.

Geological chronology, or geochronology, is based on elucidating the geological history of the most well-studied regions, for example, in Central and Eastern Europe. Based on broad generalizations, comparison of the geological history of various regions of the Earth, patterns of evolution of the organic world at the end of the last century, at the first International Geological Congresses, the International Geochronological Scale was developed and adopted, reflecting the sequence of time divisions during which certain sediment complexes were formed, and the evolution of the organic world . Thus, the international geochronological scale is a natural periodization of the history of the Earth.

Among the geochronological divisions are distinguished: eon, era, period, epoch, century, time. Each geochronological subdivision corresponds to a set of deposits, identified in accordance with the change in the organic world and called stratigraphic: eonoteme, group, system, department, stage, zone. Therefore, the group is a stratigraphic unit, and the corresponding temporal geochronological unit is represented by an era. Therefore, there are two scales: geochronological and stratigraphic. The first is used when talking about relative time in the history of the Earth, and the second when dealing with sediments, since some geological events occurred in every place on the globe in any period of time. Another thing is that the accumulation of precipitation was not ubiquitous.

The Archean and Proterozoic eonotemes, covering almost 80% of the time of the Earth's existence, are distinguished in the Cryptozoic, since the skeletal fauna is completely absent in the Precambrian formations and the paleontological method is not applicable to their division. Therefore, the division of Precambrian formations is based primarily on general geological and radiometric data.
The Phanerozoic eon covers only 570 million years, and the division of the corresponding eonoteme of deposits is based on a wide variety of numerous skeletal fauna. The Phanerozoic eonoteme is subdivided into three groups: Paleozoic, Mesozoic and Cenozoic, corresponding to major stages in the natural geological history of the Earth, the boundaries of which are marked by rather abrupt changes in the organic world.

The names of eonotems and groups come from Greek words:

"archeos" - the most ancient, most ancient;
"proteros" - primary;
"paleos" - ancient;
"mesos" - medium;
"kainos" - new.

The word "cryptos" means hidden, and "phanerozoic" means explicit, transparent, since the skeletal fauna appeared.
The word "zoi" comes from "zoikos" - life. Therefore, "Cenozoic era" means the era of new life, and so on.

Groups are subdivided into systems, the deposits of which were formed during one period and are characterized only by families or genera of organisms characteristic of them, and if these are plants, then by genera and species. Systems have been identified in different regions and at different times since 1822. At present, 12 systems are distinguished, the names of most of which come from the places where they were first described. For example, the Jurassic system - from the Jura Mountains in Switzerland, the Permian - from the Perm province in Russia, the Cretaceous - according to the most characteristic rocks - white writing chalk, etc. The Quaternary system is often called Anthropogenic, since it is in this age interval that a person appears.

The systems are subdivided into two or three divisions, which correspond to the early, middle, and late eras. The departments, in turn, are divided into tiers, which are characterized by the presence of certain genera and species of fossil fauna. And, finally, the stages are subdivided into zones, which are the most fractional part of the international stratigraphic scale, which corresponds to time in the geochronological scale. The names of the stages are usually given according to the geographical names of the regions where this stage was distinguished; for example, the Aldanian, Bashkirian, Maastrichtian stages, etc. At the same time, the zone is designated by the most characteristic type of fossil fauna. The zone covers, as a rule, only a certain part of the region and is developed over a smaller area than the deposits of the stage.

All subdivisions of the stratigraphic scale correspond to the geological sections in which these subdivisions were first identified. Therefore, such sections are reference, typical, and are called stratotypes, which contain only their own complex of organic remains, which determines the stratigraphic volume of a given stratotype. The determination of the relative age of any layers consists in comparing the discovered complex of organic remains in the studied layers with the complex of fossils in the stratotype of the corresponding division of the international geochronological scale, i.e. the age of the deposits is determined relative to the stratotype. That is why the paleontological method, despite its inherent shortcomings, remains the most important method for determining the geological age of rocks. Determining the relative age of, for example, the Devonian deposits only indicates that these deposits are younger than the Silurian, but older than the Carboniferous. However, it is impossible to establish the duration of the formation of the Devonian deposits and give a conclusion about when (in absolute chronology) the accumulation of these deposits occurred. Only methods of absolute geochronology are able to answer this question.

Tab. 1. Geological table

Era	Period	Epoch	Duration, Ma	Time from the beginning of the period to the present day, million years	Geological conditions	Vegetable world	Animal world
Cenozoic (time of mammals)	Quaternary	Modern	0,011	0,011	End of the last ice age. The climate is warm	The decline of woody forms, the flowering of herbaceous	Age of Man
	Quaternary	Pleistocene	1	1	repeated glaciations. four ice ages	Extinction of many plant species	Extinction of large mammals. The origin of human society
	Tertiary	Pliocene	12	13	The uplift of mountains in the west of North America continues. Volcanic activity	Decay of forests. Spread of meadows. flowering plants; development of monocots	The emergence of man from the great apes. Types of elephants, horses, camels, similar to modern
		Miocene	13	25	The Sierras and the Cascade Mountains formed. Volcanic activity in the northwestern United States. The climate is cool		The culminating period in the evolution of mammals. The first great apes
		Oligocene	11	30	The continents are low. The climate is warm	Maximum distribution of forests. Strengthening the development of monocotyledonous flowering plants	Archaic mammals are dying out. The beginning of the development of anthropoids; ancestors of most extant genera of mammals
		Eocene	22	58	The mountains are blurred. There are no inland seas. The climate is warm		Diverse and specialized placental mammals. Ungulates and carnivores flourish
		Paleocene	5	63			Distribution of archaic mammals
Alpine orogeny (minor destruction of fossils)
Mesozoic (time of reptiles)	Chalk		72	135	At the end of the period, the Andes, the Alps, the Himalayas, the Rocky Mountains are formed. Prior to this, inland seas and swamps. Deposition of writing chalk, shale	The first monocots. The first oak and maple forests. Decline of gymnosperms	Dinosaurs reach the highest development and die out. Toothed birds are dying out. Appearance of the first modern birds. Archaic mammals are common
	Yura		46	181	The continents are quite elevated. Shallow seas cover parts of Europe and the western United States	The value of dicots increases. Cycadophytes and conifers are common	The first toothed birds. Dinosaurs are large and specialized. Insectivorous marsupials
	Triassic		49	230	Continents are elevated above sea level. Intensive development of arid climate conditions. Widespread continental deposits	The dominance of the gymnosperms, already beginning to decline. Extinction of seed ferns	The first dinosaurs, pterosaurs and egg-laying mammals. Extinction of primitive amphibians
Hercynian orogeny (some destruction of fossils)
Paleozoic (era of ancient life)	Permian		50	280	Continents are raised. Appalachian mountains formed. Dryness is getting worse. Glaciation in the southern hemisphere	Decline of club mosses and ferns	Many ancient animals are dying out. Animal reptiles and insects develop
	Upper and Middle Carboniferous		40	320	The continents are initially low-lying. Vast swamps in which coal was formed	Large forests of seed ferns and gymnosperms	The first reptiles. Insects are common. Distribution of ancient amphibians
	Lower Carboniferous		25	345	The climate is initially warm and humid, later, due to the rise of the land, it becomes cooler.	Club mosses and fern-like plants dominate. Gymnosperms are spreading more and more	Sea lilies reach their highest development. Distribution of ancient sharks
	Devonian		60	405	Inland seas are small. Land elevation; development of an arid climate. Glaciation	First forests. Land plants are well developed. First gymnosperms	The first amphibians. Abundance of lungfish and sharks
	Silurus		20	425	Vast inland seas. Low-lying areas are getting drier as the land rises	The first reliable traces of land plants. Algae dominate	Marine arachnids dominate. The first (wingless) insects. Increased development of fish
	Ordovician		75	500	Significant land sink. The climate is warm, even in the Arctic	Probably the first land plants appear. Abundance of seaweed	The first fish are probably freshwater. Abundance of corals and trilobites. Various clams
	Cambrian		100	600	The continents are low, the climate is temperate. The most ancient rocks with abundant fossils	Seaweed	Trilobites and lechenopods dominate. The origin of most modern animal phyla
Second great orogeny (significant destruction of fossils)
Proterozoic			1000	1600	Intensive process of sedimentation. Later - volcanic activity. Erosion over large areas. Multiple glaciations	Primitive aquatic plants - algae, fungi	Various marine protozoa. By the end of the era - molluscs, worms and other marine invertebrates
First great mountain building (significant destruction of fossils)
archaeus			2000	3600	Significant volcanic activity. Weak sedimentation process. Erosion on large areas	Fossils are absent. Indirect evidence of the existence of living organisms in the form of deposits of organic matter in rocks

The problem of determining the absolute age of rocks, the duration of the existence of the Earth has long occupied the minds of geologists, and attempts to solve it have been made many times, for which various phenomena and processes have been used. Early ideas about the absolute age of the Earth were curious. A contemporary of M. V. Lomonosov, the French naturalist Buffon determined the age of our planet at only 74,800 years. Other scientists gave different figures, not exceeding 400-500 million years. It should be noted here that all these attempts were doomed to failure in advance, since they proceeded from the constancy of the rates of processes, which, as is known, changed in the geological history of the Earth. And only in the first half of the XX century. there was a real opportunity to measure the really absolute age of rocks, geological processes and the Earth as a planet.

Tab.2. Isotopes used to determine absolute ages
parent isotope	Final product	Half-life, billion years
147cm	143 Nd+He	106
238 U	206 Pb+ 8 He	4,46
235 U	208 Pb+ 7 He	0,70
232Th	208 Pb+ 6 He	14,00
87Rb	87 Sr+β	48,80
40K	40 Ar+ 40 Ca	1,30
14C	14 N	5730 years

The history of the scale. Geochronological scale and history of the development of living organisms International geochronological scale table

Geological scale