Geological chronology. Summary of a geography lesson on the topic "Geological chronology and geological map" (8th grade)

Topic: Geological chronology and geological map."

Lesson objectives:

repeat the basic concepts of the topic: “Lithosphere and relief”,

introduce the sciences that study the earth's crust. To form an idea of the geochronological table, to give knowledge about geological chronology.

consider the biological evolution of life on Earth, without deepening this issue, - develop students’ skills in establishing cause-and-effect relationships;

continue to form ideas about interdisciplinary connections;

promote students' cognitive activity and interest in the subjects they study with the help of new information technologies.

Equipment: computer, projector, collection of minerals, physical map of Russia, geochronological table, tectonic map of Russia.

During the classes:

I. Organizational moment.

II. Historical reference.

Teacher. Modern relief of the planet –this is the result of long-term geological development and the influence of modern relief-forming processes: internal (endogenous) and external (exogenous), including humans. To understand the differences in modern relief, you need to know the geological history of its formation. Science studies the structure and history of the development of the Earth based on the location of rocks -geology . For many years, geologists, studying rocks, tried to determine the age of the Earth. But until recently they were far from success. In the early 17th century, Archbishop of Armagh James Ussher calculated the date of creation from the Bible and determined it to be 4004 BC. e. But he was more than a million times wrong. Today scientists believe that the age of the Earth is 4600 million years. It is approximately equal to the age of the Sun and other planets.

Geology is divided into branches:

Historical Geology – studies the patterns of the structure of the earth's crust over geological time.

Geotectonics – the doctrine of the structure of the earth's crust and the formation of tectonic structures (folds, faults, cracks, etc.)

Paleontology – This is the science of extinct organisms that are studied through fossils, preserved hard skeletons, etc.

Mineralogy – the science that studies minerals.

Petrography - a science that studies rocks. Geochronology studies the age, duration, and sequence of formation of rocks.

Geochronological method – based on the study of the sequence of sedimentary rocks.

– What are sedimentary rocks called?
– Explain the mechanism of formation of sedimentary rocks (Under the influence of weather conditions, rocks are destroyed, rivers carry their fragments into lakes and seas, where sedimentary rocks are formed from accumulating sediments )
- Give examples. (Show samples)

III. Explanation of new material.

Teacher. When studying the age of the Earth, they compiled the Earth calendar. The history of the Earth is divided into long periods of time -era. Eras are divided intoperiods , periods forera , eras – oncentury . (Write in notebook)
Names of eras of Greek origin:Archean - the oldest,Proterozoic – early,Paleozoic – ancient,Mesozoic- average,Cenozoic – new. Based on determining the geological age of rocks, scientists compile geochronological tables. Reading of such tables begins from the bottom as the rocks occur. In our lesson we will draw up a table in which we will enter the most important geological events, minerals, and trace the main stages of the development of life and the stages of chemical evolution.(Filling out the table while learning new material)

Teacher. Protoplanetary stage – the emergence of the Universe. Any electron that tried to approach the high-energy proton was immediately thrown away as a result of a collision with it. But time worked against radiation. The expansion cooled the Universe and protons gradually lost their energy as they had to fill more and more space. After about a million years, the temperature dropped to 4000 C, which already allowed the nuclei to hold electrons in orbits. It was at this stage of the development of the Universe that atoms were formed. Over the course of several thousand years, electrons settled into orbits around hydrogen nuclei. Planet Earth was formed from clumps of dust, gas and harder particles. Meteorites often fell into this clot, which increased the temperature of the young planet. Gradually, the swarm of meteorites dispersed, and the era of volcanism began. The lava erupted by volcanoes solidified, and the primary appearance of the Earth was formed.

Teacher. Precambrian period . In geology, during this period, the primary earth's crust is formed, which grows through the process of volcanism and sedimentary rocks. This is how large platforms were formed. Life in the Precambrian period became a geological factor - living organisms changed the shape and composition of the earth's crust, forming its upper layer - the biosphere.

Questions.

– Name and show them on the map.
– What do they correspond to in relief?(Russian and West Siberian plains)

The foundations of the platforms are composed of igneous and metamorphic rocks.

– What rocks are called igneous and metamorphic? Give examples.(Gneisses, granites, quartzites - display of minerals from the collection)

During the Precambrian period, folded areas were formed in the south of the Siberian Platform.

– What are folded areas called?
– How are they formed?

– What do they correspond to in relief? Name them and show them on the map.(Mountains of the Baikal region and Transbaikalia)

Precambrian minerals are characterized by high ore content (magnetic iron ore, red iron ore, copper pyrite, lead luster - display of minerals).

Teacher. Palaeozoic . In the Paleozoic era, as a result of the collision of lithospheric plates, land mountains were formed. From their very origins, animals have been dependent on plants, which supply them with oxygen and stand at the base of the food pyramid. Tell us about the animals and plants that originated in the Paleozoic era.

– Determine from the map which mountains were formed during this period?(Ural Mountains, Altai, Western and Eastern Sayans) . As a result of the abundance of vegetation and wildlife during this period, oil, coal, and salts are formed. Carboniferous and Permian coals make up 40% of the Earth's coal reserves.

Display of minerals.

Teacher. Mesozoic era. Using a tectonic map, determine the territories whose formation took place during the Mesozoic era?(Sikhote-Alin Mountains; Chersky and Verkhoyansky ridges). This is the era of reptiles and gymnosperms. Reptiles have populated all land and sea, some have adapted to flight. Dinosaurs became the complete “masters” of land.

– Name the minerals of the Mesozoic era.(Gold, zinc, arsenic, silver, tin, tungsten and others)
These minerals arose as a result of active tectonic movements. Currently, the diversity of the relief of these territories is the result of geological history.
Part of the oceanic plate sank, and individual blocks rose, subsequently forming platforms. Under conditions of a warm and humid climate and high biomass, coal deposits were formed. The largest Zyryansky coal basin, the thickness of the layers is 700-800 meters(show on map).

Teacher. Cenozoic era. With the beginning of the Cenozoic era, the continents of Laurasia and Gondwana began to “spread away”, forming new continents. At the same time, lithospheric plates moved and collided with each other. This is how folds were formed, i.e. mountain ranges.

In the Cenozoic era in Russia, folding occurred within the Alpine-Himalayan and Pacific belts. This corresponds to the North Caucasus (Fig. 67, 68), where mountains grow, as evidenced by volcanism and earthquakes. Here lies the boundary of the collision of the Eurasian and African-Arabian lithospheric plates. The Kuril Islands and Kamchatka correspond to the Pacific belt (Fig. 69,70). The laying of the continental crust continues here, so earthquakes, geysers, and volcanism are observed.

Questions:

– Show the Kuril Islands and the Kamchatka Peninsula on the map.
– Name the largest volcano in Russia.
– Show the Caucasus Mountains and the highest peak in Russia.

Mineral resources include phosphorites, brown coals, bauxites, diamonds, and precious stones.

During the Quaternary period, glaciation begins. During this period, there is an alternation of rising and falling temperatures. There are 3 glaciations in Russia: Oka, Dnieper, and Valdai. The last post-glacial era lasts 10 thousand years.Cenozoic - the era of flowering plants, birds and mammals.

Consolidation.

The science that studies the structure and history of the development of the Earth is called...(geology ).

The doctrine of the structure of the earth's crust and its movements is called - ... (geotectonics )

The branch of geology that deals with the study of the age, duration and sequence of formation of rocks...(geochronology )

The longest periods of time in the geological history of the Earth are...(era )

The most ancient era is…(Archean )

We live in an era of new life...(Cenozoic )

A table containing information about the successive change of eras and periods, the most important geological events, and stages of life development is called ...(geochronological )

Using the table, find the period in which ancient glaciation occurred (quaternary or anthropogenic )

The most ancient mountain formation is called (Baikal folding )

The youngest mountains were formed in...(alpine ) folding.

Lesson summary.

– What stages of the development of the Earth have we identified?
– How has the appearance of the Earth changed over 4.6 million years?
– What processes shaped the appearance of the Earth?
– What happened to living organisms at this time?
– What are your impressions about the development of life on Earth?

Homework: item 11, finish the table and learn it.

The term geological sources of information refers to material samples and information that allow one to evaluate historical data and draw up a detailed geological plan. Sources of information include:

Fossil maps - they contain detailed information about the localization of deposits, existing patterns and promising areas for development. All geological maps have a scale, depending on the size of which they distinguish: overview territorial maps, reflecting information about continents, states, etc.;

Medium-scale maps - record the territorial characteristics of individual areas, for example, Altai, Caucasus, etc.; small scale maps - regional data or geological information of small states.

Relative chronology

In the Paleozoic:

2. Ordovician – vertebrates;

3. Silur – terrestrial plants;

In the Mesozoic:

2. Yura - the first birds;

In the Cenozoic:

1. Paleogene – first flowers;

Absolute chronology

Tree rings are found in rock formed by sediments. Seasonal deposits are considered in the study areas. In summer, the sedimentary layer is formed by sandstone and is thicker. In winter, when rock movement is less intense, silt and clay settle. The age of the layer is determined by the number of clay and sand layers. To obtain accurate data, when using the sedimentary method, nothing should interfere with the process of rock accumulation. If the rhythm is disrupted and the process is interrupted, the data may be distorted. Another limitation of this method is the study period; it is impossible to determine the age of a rock older than several tens of thousands of years.

The radiation dating method is based on taking into account the decay rate of radioisotopes within the rock. The idea of using background radiation as a geological tool was proposed by P. Curie in 1902. The advantage of the technique is the fact that the rate of decay of radioactive particles is constant, which is not affected by climatic or other factors. Essentially, the radiation dating method consists of many methods, in particular: uranium-lead, rubidium-strontium, potassium-argon, lead-isotope, samarium-neodymium, radiocarbon. The methodology is based on natural physical processes that cause the transformation of atmospheric nitrogen into radioactive fallout with a decay period of 5.57 thousand years.

The method is used for dating peat, wood and other carbon-containing compositions. Based on the methodology, the duration of each of the existing eras was identified, and the boundaries of the periods included in them were determined. Geological sources of information The term geological sources of information refers to material samples and information that allow one to evaluate historical data and draw up a detailed geological plan. Sources of information include:

Data on mineral deposits - their volume, location, conditions of occurrence and methods of extraction;
Factual material – soil samples, etc.;
Reports on measurements over geological objects;
Tables, reports, graphs, maps and other analytical material;
Information on the costs of exploration and extraction of minerals.

The most accessible source of obtaining the information in question is considered to be geological maps.

Geological map is a graphical complex of data reflecting the characteristics and structure within the boundaries of a certain zone or on a planetary scale. The data reflected in the map has its own symbols and is plotted using special symbols. A geological map reflects information about the age, size, composition and conditions of rock outcrops on the Earth's surface.

Based on geological maps, conclusions can be drawn about the patterns of accumulation and distribution of minerals, both in a single territory and on the entire planet. The information contained in the map makes it possible to evaluate and trace the stages of formation of the earth's crust.

To create maps, data obtained during geological exploration expeditions, when analyzing theoretical material, etc. are used. Depending on the purpose and content of cards, the following types are distinguished:

Stratigraphic geological maps - cover the period up to Quaternary rocks. The materials do not disclose information regarding continental sediments, the exception may be their significant thickness or the lack of knowledge of the underlying rocks. The map symbolically displays the origin, composition, age, occurrence conditions and delineation features;
Quaternary sediment maps - displays Quaternary rocks divided by age, composition and genesis. By studying the material, one can see the stages of glaciation, the localization and distribution of glacial rocks, marine regressions and transgressions;
Lithography maps - reflect information about the burial conditions and composition of surface outcrops or rocks located below the Quaternary level;
Geomorphology maps - inform about the main types of relief or individual elements, taking into account their origin and age;
Tectonics maps - show the forms, conditions and time of formation of the structural components of the Earth's crust;
Hydrogeological map - reveals information about the composition and regimes of underground reservoirs, aquifers, conditions of water occurrence;
Engineering-geological maps - show the properties of rocks and geodynamic phenomena;
Fossil maps - they contain detailed information about the localization of deposits, existing patterns and promising areas for development.

All geological maps have a scale, depending on the size of which they distinguish: overview territorial maps, reflecting information about continents, states, etc.; Medium-scale maps - record the territorial characteristics of individual areas, for example, Altai, Caucasus, etc.; small scale maps - regional data or geological information of small states.

Relative chronology

The chronological sequence of geological events is reflected in a single, systematized and internationally recognized geochronological table or scale. This material shows the duration of periods of development and the duration of eras, as well as their sequence.

According to the scale, five eras are distinguished, these are: Archaea - 1800 million (bacteria, algae); Proterozoic – 2000 million (the first multicellular organisms); Paleozoic – 330 million; Mesozoic – 165 million; Cenozoic – 70 million

Geological era defines one of the stages of life and development of the organic world and the earth's crust. Eras, starting with the Paleozoic, were divided into periods. There are 12 periods in total:

In the Paleozoic:
1. Cambrian – invertebrate inhabitants of the sea;

2. Ordovician – vertebrates;

3. Silur – terrestrial plants;

4. Devonian – fish and amphibians;
5. Carboniferous – amphibians, ferns;
In the Mesozoic:

1. Triassic – the first mammals;

2. Yura - the first birds;

3. Chalk – death of large reptiles, dominance of birds and mammals.

In the Cenozoic:

1. Paleogene – first flowers;

2. Neogene - development and wide distribution of flowers, mammals and birds;

3. Anthropocene – the origin and development of man.

The relationship of different time units, when considering geological events, is denoted by the term relative geochronology. The methodology is based on lithostratigraphy - stratigraphic analysis based on the comparison of layers with similar compositions and characteristics.

Lithostratigraphy is a technique for identifying and dividing conventional periods of time. The ability to trace and evaluate the relative sequence of superpositions and correlate related events emerged in the 17th century. The law confirming the existence of a sequence was formulated by Nikolaus Steno in 1669. It was he who determined the relationship between the depth of the rock and its age. A stratigraphic break was also identified - a violation of the sequence of strata.

Despite the recognized importance of Steno's law, this principle is limited by a number of features. The principle is relevant for regions with low tectonic activity, with a characteristic horizontal formation of layers. When layers are compressed as a result of tectonic phenomena and mixed, the data obtained by the Steno method will be inaccurate. In this case, paleontological methods are used that study fossils and determine the age of rocks based on the remains of biological material. Evolutionary analysis allows one to determine relative age more accurately and is used as a basis.

Absolute chronology

Absolute chronology is a technique that allows one to determine the age of a rock with an accuracy of several years.

This type of chronology operates on two types of methods: sedimentary radiological.

In the first case, the rate of precipitation accumulation is taken into account; the method has another name - seasonal-climatic. All living things on Earth have natural mechanisms for recording periods of life, a striking example is the tree rings. Formations that depend on climate change and the passage of time make it possible to determine the age of the object under study.

To obtain accurate data, when using the sedimentary method, nothing should interfere with the process of rock accumulation. If the rhythm is disrupted and the process is interrupted, the data may be distorted. Another limitation of this method is the study period; it is impossible to determine the age of a rock older than several tens of thousands of years.

Essentially, the radiation dating method consists of many methods, in particular: uranium-lead, rubidium-strontium, potassium-argon, lead-isotope, samarium-neodymium, radiocarbon. The methodology is based on natural physical processes that cause the transformation of atmospheric nitrogen into radioactive fallout with a decay period of 5.57 thousand years.

Geological chronology and geochronological table
Of great importance for geographical science is the ability to determine the age of the Earth and the earth's crust, as well as the time of significant events that occurred in the history of their development.
The history of the development of planet Earth is divided into two stages: planetary and geological.
The planetary stage covers the period of time from the birth of the Earth as a planet to the formation of the earth's crust. The scientific hypothesis about the formation of the Earth (as a cosmic body) appeared on the basis of general views on the origin of other planets that are part of the Solar System. You know from the 6th grade course that the Earth is one of the 9 planets in the solar system. Planet Earth was formed 4.5-4.6 billion years ago. This stage ended with the appearance of the primary lithosphere, atmosphere and hydrosphere (3.7-3.8 billion years ago).
From the moment the first rudiments of the earth's crust appeared, a geological stage began, which continues to the present day. During this period, various rocks were formed. The earth's crust has repeatedly been subjected to slow uplift and subsidence under the influence of internal forces. During the period of subsidence, the territory was flooded with water and sedimentary rocks (sands, clays, etc.) were deposited at the bottom, and during periods of rising the seas retreated and in their place a plain composed of these sedimentary rocks arose.
Thus, the original structure of the earth's crust began to change. This process continued continuously. At the bottom of the seas and continental depressions, a sedimentary layer of rocks accumulated, among which the remains of plants and animals could be found. Each geological period corresponds to their individual species, because the organic world is in constant development.
Determining the age of rocks. In order to determine the age of the Earth and present the history of its geological development, methods of relative and absolute chronology (geochronology) are used.
To determine the relative age of rocks, it is necessary to know the patterns of sequential occurrence of layers of sedimentary rocks of different compositions. Their essence is as follows: if layers of sedimentary rocks lie in an undisturbed state in the same way as they were deposited one after another on the bottom of the seas, then this means that the layer lying below was deposited earlier, and the layer lying above was formed later, therefore , he's younger.
Indeed, if there is no lower layer, then it is clear that the upper layer covering it cannot form, therefore the lower the sedimentary layer is located, the older its age. The topmost layer is considered the youngest.
In determining the relative age of rocks, the study of the successive occurrence of sedimentary rocks of different compositions and the fossilized remains of animal and plant organisms contained in them is of great importance. As a result of the painstaking work of scientists to determine the geological age of rocks and the time of development of plant and animal organisms, a geochronological table was compiled. It was approved at the II International Geological Congress in 1881 in Bologna. It is based on the stages of life development identified by paleontology. This scale table is constantly being improved. The current state of the table is shown on p. 43.
The units of the scale are eras, divided into periods which are subdivided into epochs. The five largest of these divisions - eras - bear names associated with the nature of life that existed then. For example, Archean is the time of earlier life, Proterozoic is the era of primary life, Paleozoic is the era of ancient life, Mesozoic is the era of middle life, Cenozoic is the era of new life.
Eras are divided into shorter periods of time - periods. Their names are different. Some of them come from the names of rocks that are most characteristic of this time (for example, the Carboniferous period in the Paleozoic and the Mothic period in the Mesozoic). Most periods are named after the localities in which the deposits of a particular period are most fully developed and where these deposits were first characterized. The oldest period of the Paleozoic - the Cambrian - received its name from Cambria, an ancient state in the west of England. The names of the following periods of the Paleozoic - Ordovician and Silurian - come from the names of the ancient tribes of the Ordovicians and Silurians who inhabited the territory of what is now Wales.
To distinguish the systems of the geochronological table, conventional signs are adopted. Geological eras are designated by indices (signs) - the initial letters of their Latin names (for example, Archaean - AR), and period indices - by the first letter of their Latin names (for example, Permian - P).
Determination of the absolute age of rocks began at the beginning of the 20th century, after scientists discovered the law of decay of radioactive elements. In the depths of the Earth there are radioactive elements, such as uranium. Over time, it slowly, at a constant rate, decays into helium and lead. The helium dissipates, but the lead remains in the rock. Knowing the rate of decay of uranium (from 100 g of uranium, 1 g of lead is released over 74 million years), from the amount of lead contained in the rock, we can calculate how many years ago it was formed.
The use of radiometric methods has made it possible to determine the age of many rocks that make up the earth's crust. Thanks to these studies, it was possible to establish the geological and planetary age of the Earth. Based on the relative and absolute methods of chronology, a geochronological table was compiled.
1. What stages is the geological history of the Earth’s development divided into?
2. Which stage of the Earth’s development is geological? 3.* How is the age of rocks determined?
4. Compare the duration of geological eras and periods using the geochronological table.

- the doctrine of the chronological sequence of formation and age of rocks that make up the earth's crust. Geological processes occur over many millennia. The identification of various stages and periods in the life of the Earth is based on the sequence of accumulation of sedimentary rocks. The time at which each of the five groups of rocks accumulated is called era. The last three eras are divided into periods, because... In the sediments of these times, the remains of animals and plants were better preserved. In the eras there were eras of intensification of mountain-building processes - folding.

Geochronological table

Eras	Periods	Folding	Events
Cenozoic , 68 million years	Quaternary, 2 million years	Alpine folding	Formation of modern relief under the influence of massive land uplift. Glaciation, sea level changes. Human Origins.
	Neogene, 25 million years		Powerful volcanic eruptions, uplift of the Alpine mountains. Mass distribution of flowering plants.
	Paleogene, 41 million years		Destruction of mountains, flooding of young platforms by seas. Development of birds and mammals.
Mesozoic , 170 million years	Cretaceous, 75 million years old	Mesozoic folding	The rise of destroyed mountains formed in the Baikal fold. The disappearance of giant reptiles. Origin of angiosperms.
	Jurassic, 60 million years		The emergence of faults on continents, massive input of igneous rocks. The beginning of the exposure of the bed of modern seas. Hot humid climate.
	Triassic, 35 million years		Recession of the seas and increase in land area. Weathering and lowering of Paleozoic mountains. Formation of flat terrain.
Paleozoic , 330 million years	Permian, 45 million years	Hercynian folding	The end of the Hercynian mountain formation, the intensive development of life in the mountains. The appearance of amphibians, simple reptiles and insects on land.
	Carboniferous, 65 million years		Lowering the land. Glaciation on the continents of the Southern Hemisphere. Expansion of swamp areas. The emergence of a tropical climate. Intensive development of amphibians.
	Devonian, 55 million years	Caledonian folding	Retreat of the seas. The accumulation on land of thick layers of red continental sediment. Predominance of hot, dry climate. Intensive development of fish, emergence of life from the sea to land. The appearance of amphibians and open-seeded plants.
	Silurian, 35 million years old	Beginning of the Caledonian folding	Rising sea levels, appearance of fish.
	Ordovician, 60 million years		Strong volcanic eruptions, shrinking sea basins. An increase in the number of invertebrate animals, the appearance of the first invertebrates.
	Cambrian, 70 million years	Baikal folding	Subsidence of land and the appearance of large swampy areas. Invertebrates develop intensively in the seas.
	Proterozoic, 2 billion years	The beginning of the Baikal folding	Powerful volcanic eruptions. Formation of the foundations of ancient platforms. Development of bacteria and blue-green algae.
	Archean, 1 billion years		The beginning of the formation of the continental crust and the intensification of magmatic processes. Powerful volcanic eruptions. The first appearance of life is the period of bacteria.

Age of rocks

Distinguish between relative and absolute rock age . The relative age is easily established in the case of horizontal occurrence of rock layers within the same exposure. The absolute age of rocks is quite difficult to determine. To do this, they use the method of radioactive decay of a number of elements, the principle of which does not change under the influence of external conditions and proceeds at a constant speed. This method was introduced into science at the beginning of the 20th century by Pierre Curie and Ernest Rutherford. Depending on the final decay products, lead, helium, argon, calcium, strontium and radiocarbon methods are distinguished.

Paleontology, one of the most fascinating biological sciences, is closely related to geology. She studies the fossil remains of animals and plants, determines their systematic position in the general hierarchy of the organic world and establishes the patterns of evolutionary development.

Based on the stages of development of the organic world and the mineral composition of the sedimentary formations that host them during the 19th century. All currently known and widely used stratigraphic units were established - erathems, systems, divisions, stages. One of the large stratigraphic units is the erathema, which includes several systems. In turn, systems consist of departments and tiers. Each stratigraphic unit is assigned its own name.

In accordance with the stratigraphic units, geochronological divisions were identified, each of which reflects the duration (again in relative terms) of the formation of the corresponding stratigraphic divisions.

The time interval required for the formation of a group is designated as a geological era, the time of formation of the system corresponds to the geological period, the department - the era and stage - the geological age.

Geological chronology

Geologists have long noticed that the history of our planet is divided into two unequal parts. The older, longer part of it is difficult to study using paleontological methods, since it does not contain fossil remains and, in addition, quite often the sedimentary strata are strongly altered by metamorphism. The young part of the stone record has been well studied, since the sedimentary layers in it contain numerous remains of organisms, the number and preservation of which increase as we approach the modern era. The American geologist C. Schuchert called this young part of the history of the earth's crust the Phanerozoic eon, i.e., the time of obvious life. An eon is a period of time that unites several geological eras. Its stratigraphic equivalent is the eonothem.

C. Schuchert called the more ancient and longer part of geological history the cryptozoic, or a time with the hidden development of life. Quite often it is also called the Precambrian. This name has been preserved since the middle of the 19th century, when the vast majority of geological periods were established. More and more ancient sediments underlying the Cambrian strata began to be dated to the Precambrian. Currently, instead of the Cryptozoic, two eons are distinguished: Archean and Proterozoic.

The wide distribution, richness of fossil organic remains and relative accessibility of Phanerozoic deposits predetermined their better study. The English geologist J. Phillips in 1841 identified three eras within the Phanerozoic: Paleozoic - the era of ancient life; Mesozoic - the era of middle life and Cenozoic - the era of new life. In the Paleozoic, marine invertebrates, fish, amphibians and spore plants dominated, in the Mesozoic - reptiles and gymnosperms, and in the Cenozoic - mammals and angiosperms.

Deposits formed during a geological era are called erathems. Smaller stratigraphic units are systems, divisions and stages. The names of the systems and stages were given mainly by the names of the areas where they were established and studied, or by some characteristic features. Thus, the name of the Jurassic system comes from the Jurassic Mountains in Switzerland, the Permian - from the city of Perm, the Cambrian from the ancient name of the English province of Wales, the Cretaceous - from the widespread writing chalk, the Carboniferous - from coal, etc.

If the stratigraphic scale reflects the sequence of deposits and their subordination, then the geochronological scale determines the duration and natural sequence of stages in the historical development of the Earth. Over the past 100 years, the geochronological and stratigraphic scales of the Phanerozoic have been revised many times.

However, in geology it is important to know not only the relative age of rocks, but also, if possible, the exact time of their origin. Several different methods based on the phenomenon of radioactive decay are used to determine the age of rocks. In this regard, the age of rocks is called radiogeochronometric. To determine it, radioactive isotopes of uranium, thorium, rubidium, potassium, carbon and hydrogen are used. Due to the fact that we know the decay rate of a radioactive isotope, we can easily determine the age of the mineral, and therefore the rock. Currently, various methods of nuclear geochronology have been developed and are widely used: uranothorium-lead, uranothorium-helium, uranium-xenon, potassium-argon, rubidium-strontium, samarium-niodymium, rhenium-osmium and radiocarbon. The content of radioactive isotopes in rocks and minerals is determined in special devices - mass spectrometers.

Thanks to the methods of nuclear geochronology, the age of igneous and sedimentary rocks is determined, and for metamorphic rocks the time of exposure to high temperatures and pressure is determined. The isotopic age of the most ancient rocks on the globe is 3.8-4 billion years. Some lunar rocks and meteorites are close in age.

The difficulty of studying Archean and Proterozoic deposits predetermined their weak stratigraphic and geochronological division. This is what the Archean-Proterozoic scale, which is far from perfect and detailed, currently looks like.

In geology, an additional method of age division and comparison of sediments is also used. This is a paleomagnetic method based on the phenomenon of preservation of magnetic properties in rock strata. Rocks containing magnetic minerals have ferromagnetic (magnetized) properties and, under the influence of the Earth's magnetic field, acquire natural remanent magnetization. It has now been proven that over the course of a long geological history, the position of the magnetic poles has changed several times. By establishing the remanent magnetization and its direction (i.e., vector) and comparing the vectors with each other, it is possible to establish the same age of rocks, which to a certain extent clarifies the geochronological scale.

The main stages of the formation of the earth's crust

Determining the age of various igneous rocks made it possible not only to determine the duration of geological periods, but also to identify the most ancient rocks of the Earth. It is now known that documented traces of life on Earth arose over 3 billion years ago, the oldest sedimentary rocks are just over 3.8 billion years old, and the age of the Earth is estimated at 4.6-5 billion years, although some scientists consider these figures to be overestimated.

It has been established that epochs of intense volcanic activity were short-lived and separated by long epochs with weak manifestations of magmatism. Epochs of enhanced magmatism were characterized by a high degree of tectonic activity, that is, significant vertical and horizontal movements of the earth's crust.