The stratigraphic scale (geochronological) is a standard by which the history of the Earth is measured in terms of time and geological magnitude. is a kind of calendar that counts time intervals in hundreds of thousands and even millions of years.

About the planet

The current conventional wisdom about the Earth is based on various data, according to which the age of our planet is approximately four and a half billion years. Neither rocks nor minerals that could indicate the formation of our planet have yet been found either in the bowels or on the surface. Refractory compounds rich in calcium, aluminum and carbonaceous chondrites, which were formed in the solar system before anything else, limit the maximum age of the Earth to these figures. The stratigraphic scale (geochronological) shows the boundaries of time from the formation of the planet.

A variety of meteorites were studied using modern methods, including uranium-lead, and as a result, estimates of the age of the solar system were presented. As a result, the time that has elapsed since the creation of the planet was divided into time intervals according to the most important events for the Earth. The geochronological scale is very convenient for tracking geological times. The eras of the Phanerozoic, for example, are delimited by the largest evolutionary events when the global extinction of living organisms occurred: the Paleozoic on the border with the Mesozoic was marked by the largest extinction of species in the entire history of the planet (Permo-Triassic), and the end of the Mesozoic is separated from the Cenozoic by the Cretaceous-Paleogene extinction.

History of creation

For the hierarchy and nomenclature of all modern subdivisions of geochronology, the nineteenth century turned out to be the most important: in its second half, sessions of the IGC - the International Geological Congress took place. After that, from 1881 to 1900, a modern stratigraphic scale was compiled.

Its geochronological "stuffing" was later repeatedly refined and modified as new data became available. Quite different signs have served as themes for specific names, but the most common factor is geographical.

Titles

The geochronological scale sometimes associates the names with the geological composition of the rocks: the carboniferous one appeared in connection with the huge number of coal seams during excavations, and the chalk one simply because writing chalk spread throughout the world.

Construction principle

To determine the relative geological age of the rock, a special geochronological scale was needed. Eras, periods, that is, age, which is measured in years, is of little importance to geologists. The entire lifetime of our planet was divided into two main segments - Phanerozoic and Cryptozoic (Precambrian), which are delimited by the appearance of fossil remains in sedimentary rocks.

Cryptozoic is the most interesting thing hidden from us, since the soft-bodied organisms that existed at that time did not leave a single trace in sedimentary rocks. Periods of the geochronological scale, such as the Ediacaran and Cambrian, appeared in the Phanerozoic through the research of paleontologists: they found in the rock a large variety of mollusks and many species of other organisms. Findings of fossil fauna and flora allowed them to dissect the strata and give them the appropriate names.

Time slots

The second largest division is an attempt to designate the historical intervals of the life of the Earth, when the four main periods were divided by the geochronological scale. The table shows them as primary (Precambrian), secondary (Paleozoic and Mesozoic), tertiary (almost the entire Cenozoic) and Quaternary - a period that is in a special position, because although it is the shortest, it is replete with events that left bright and well-read traces.

Now, for convenience, the geochronological scale of the Earth is divided into 4 eras and 11 periods. But the last two of them are divided into 7 more systems (epochs). No wonder. It is the last segments that are especially interesting, since this one corresponds to the time of the appearance and development of mankind.

Milestones

For four and a half billion years in the history of the Earth, the following events have occurred:

• Pre-nuclear organisms (the first prokaryotes) appeared - four billion years ago.
• The ability of organisms to photosynthesis was discovered - three billion years ago.
• Cells with a nucleus (eukaryotes) appeared - two billion years ago.
• Multicellular organisms evolved - one billion years ago.
• The ancestors of insects appeared: the first arthropods, arachnids, crustaceans and other groups - 570 million years ago.
• Fish and proto-amphibians are five hundred million years old.
• Terrestrial plants appeared and have been delighting us for 475 million years.
• Insects have lived on the earth for four hundred million years, and plants in the same time period received seeds.
• Amphibians have been living on the planet for 360 million years.
• Reptiles (reptiles) appeared three hundred million years ago.
• Two hundred million years ago, the first mammals began to evolve.
• One hundred and fifty million years ago - the first birds tried to master the sky.
• One hundred and thirty million years ago flowers (flowering plants) blossomed.
• Sixty-five million years ago, the Earth lost the dinosaurs forever.
• Two and a half million years ago, a man appeared (the genus Homo).
• One hundred thousand years have passed since the beginning of anthropogenesis, thanks to which people have acquired their present form.
• For twenty-five thousand years, Neanderthals have not existed on Earth.

The geochronological scale and the history of the development of living organisms, merged together, albeit somewhat schematically and generally, with rather approximate dates, but provide a clear idea of ​​the development of life on the planet.

Bedding rocks

The Earth's crust is mostly stratified (where there are no disturbances due to earthquakes). The general geochronological scale is drawn up according to the location of the strata of rocks, which clearly show how their age decreases from lower to upper.

Fossil organisms also change as they move up: they become more complex in their structure, some undergo significant changes from layer to layer. This can be observed without visiting paleontological museums, but simply by going down the subway - eras that are very distant from us left their imprints on facing granite and marble.

anthropogen

The last period of the Cenozoic era is the modern stage of the earth's history, which includes the Pleistocene and Holocene. What just didn’t happen in these turbulent millions of years (specialists still think differently: from six hundred thousand to three and a half million). There were repeated changes of cooling and warming, huge continental glaciations, when the climate was humidified south of the advancing glaciers, water basins appeared, both fresh and salty. Glaciers absorbed part of the World Ocean, the level of which dropped by a hundred or more meters, due to which continents were formed.

Thus, there was an exchange of fauna, for example, between Asia and North America, when a bridge was formed instead of the Bering Strait. Closer to the glaciers, cold-loving animals and birds settled: mammoths, hairy rhinos, reindeer, musk oxen, arctic foxes, polar partridges. They spread south very far - to the Caucasus and the Crimea, to Southern Europe. Along the course of the glaciers, relict forests are still preserved: pine, spruce, fir. And only at a distance from them did deciduous forests grow, consisting of such trees as oak, hornbeam, maple, beech.

Pleistocene and Holocene

This is the era after the ice age - not yet completed and not fully lived segment of the history of our planet, which indicates the international geochronological scale. Anthropogenic period - Holocene, is calculated from the last continental glaciation (northern Europe). It was then that the land and the World Ocean received their modern outlines, and all the geographical zones of the modern Earth also took shape. The predecessor of the Holocene - the Pleistocene is the first epoch of the anthropogenic period. The cooling that began on the planet continues - the main part of this period (Pleistocene) was marked by a much colder climate than the modern one.

The northern hemisphere is experiencing the last glaciation - thirteen times the surface of glaciers exceeded modern formations even in interglacial intervals. Pleistocene plants are closest to modern ones, but they were located somewhat differently, especially during periods of glaciation. The genera and species of the fauna changed, those that adapted to the Arctic form of life survived. The southern hemisphere did not recognize such huge upheavals, so Pleistocene plants and animals are still present in many forms. It was in the Pleistocene that the evolution of the genus Homo took place - from (archanthropes) to Homo sapiens (neoanthropes).

When did mountains and seas appear?

The second period of the Cenozoic era - the Neogene and its predecessor - the Paleogene, including the Pliocene and Miocene about two million years ago, lasted about sixty-five million years. In the Neogene, the formation of almost all mountain systems was completed: the Carpathians, the Alps, the Balkans, the Caucasus, the Atlas, the Cordillera, the Himalayas, and so on. At the same time, the outlines and sizes of all sea basins changed, since they were subjected to severe drying. It was then that Antarctica and many mountainous regions glacied.

Marine inhabitants (invertebrates) have already become close to modern species, and mammals dominated on land - bears, cats, rhinos, hyenas, giraffes, deer. Great apes develop so much that Australopithecus could appear a little later (in the Pliocene). On the continents, mammals lived separately, since there was no connection between them, but in the late Miocene, Eurasia and North America nevertheless exchanged fauna, and at the end of the Neogene, the fauna migrated from North America to South America. It was then that the tundra and taiga were formed in the northern latitudes.

Paleozoic and Mesozoic eras

The Mesozoic precedes the Cenozoic era and lasted 165 million years, including the Cretaceous, Jurassic and Triassic periods. At this time, mountains were intensively formed on the peripheries of the Indian, Atlantic and Pacific oceans. Reptiles began their dominance on land, in water, and in the air. Then the first, still very primitive mammals appeared.

The Paleozoic is located on the scale before the Mesozoic. It lasted about three hundred and fifty million years. This is the time of the most active mountain building and the most intensive evolution of all higher plants. Almost all known invertebrates and vertebrates of various types and classes were formed at that time, but there were no mammals and birds yet.

Proterozoic and Archean

The Proterozoic era lasted about two billion years. At this time, the processes of sedimentation were active. Blue-green algae developed well. There was no opportunity to learn more about these distant times.

Archean is the oldest era in the recorded history of our planet. It lasted for about a billion years. As a result of active volcanic activity, the very first living microorganisms appeared.

Geologists have to deal with rock masses that have accumulated over the long geological history of the planet. It is necessary to know which of the rocks that make up the study area are younger and which are older, in what sequence they were formed, to what intervals of geological history the time of their formation belongs, and also to be able to compare the age of rock strata distant from each other.

The doctrine of the sequence of formation and age of rocks is called geochronology. Methods of relative and methods of absolute geochronology differ.

Relative geochronology

Methods of relative geochronology - methods for determining the relative age of rocks, which only fix the sequence of formation of rocks relative to each other.

These methods are based on a few simple principles. In 1669, Nicolò Steno formulated the principle of superposition, which states, that in undisturbed occurrence each overlying layer is younger than the underlying one. Note that the definition emphasizes the applicability of the principle only in conditions of undisturbed occurrence.

The method of determining the sequence of formation of layers, based on the Steno principle, is often called stratigraphic. Stratigraphy is a branch of geology that studies the sequence of formation and division of sedimentary, volcanic-sedimentary and metamorphic rocks that make up the earth's crust.

The next most important principle, known as intersection principle, formulated by James Hutton. This principle says that any body that crosses the thickness of the layers is younger than these layers.

Another important principle to be noted is that the time of transformation or deformation of rocks is younger than the age of formation of these rocks.

Let us consider the use of these principles on the example of sedimentary rock strata intruded by several secant igneous bodies.

The sequence of events is as follows. Initially, there was an accumulation of sedimentary strata of the lower layer (1), then, successively, the accumulation of overlying layers (2, 3, 4, 5), each of which is younger than the underlying one. The accumulation of sedimentary rocks in the overwhelming majority of cases occurs in the form of horizontally lying layers, which is how the formed layers (1-5) originally occurred. Later, these sequences were deformed (6), and a body of igneous rocks 7 was intruded into them. Then, again horizontally, the accumulation of the overlying layer began, overlying the intruded magmatic body. At the same time, taking into account that the formed layer lies on a leveled horizontal surface, it is obvious that its accumulation was preceded by the leveling of the territory - its erosion (8). Following the erosion of the territory, the next layer (9) accumulated. The youngest formation is magmatic body 10.
We emphasize that, considering the history of the geological development of the territory, the section of which is shown in the figure, we used only relative time, determining only the sequence of formation of bodies.

Another large group of relative geochronology methods isbiostratigraphic methods . These methods are based on the study fossils - fossil remains of organisms enclosed in layers of rocks: in layers of rocks of different ages there are different complexes of remains of organisms that characterize the development of flora and fauna in a particular geological epoch. The methods are based on the principle formulated by William Smith: sediments of the same age contain the same or similar remains of fossil organisms. This principle is supplemented by another important provision, stating that fossil flora and fauna replace each other in a certain order. Thus, the basis of all biostratigraphic methods is the provision on the continuity and irreversibility of changes in the organic world - the law of evolution of Charles Darwin. Each segment of geological time is characterized by certain representatives of flora and fauna. Determining the age of rock strata is reduced to comparing the fossils found in them with data on the time of existence of these organisms in geological history. As a rough analogy of the essence of the method, we can cite the well-known methods for determining age in archeology: if only stone tools were found during excavations, then the culture belongs to the Stone Age, the presence of bronze tools gives grounds for attributing it to the Bronze Age, etc.

Among biostratigraphic methods, the method of guiding forms has long remained the most important. Ruling forms are the remains of extinct organisms that meet the following criteria:

• these organisms existed for a short period of time,
• were distributed over a wide area
• their fossil parts are found and easily identified.

When determining the age, among the fossils found in the studied layer, the most characteristic ones are selected, then they are compared with atlases of guiding forms that describe which time interval certain forms are characteristic of. The first of these atlases was created in the middle of the 19th century by the paleontologist G. Bronn.

To date, the main biostratigraphy is method for the analysis of organic complexes. With this method, inference of relative age is based on information about the entire fossil assemblage, rather than on finds of single guide forms, which greatly improves accuracy.

In the course of geological research, the tasks are not only to dismember the strata by age and assign them to any interval of geological history, but also to compare - correlations- remote from each other coeval strata. The simplest method for identifying coeval strata is to trace the layers on the ground from one outcrop to another. Obviously, this method is effective only in conditions of good exposure. More universal is the biostratigraphic method of comparing the nature of organic remains in remote sections - layers of the same age have the same complex of fossils. This method allows for regional and global correlation of sections.

The principal model for using fossils to correlate remote sections is shown in the figure.

Layers containing the same complex of fossils are of the same age.

Absolute geochronology

The methods of absolute geochronology make it possible to determine the age of geological objects and events in units of time. Among these methods, the most common methods are isotope geochronology, based on calculating the decay time of radioactive isotopes contained in minerals (or, for example, in the remains of wood or in petrified animal bones).

The essence of the method is as follows. Some minerals contain radioactive isotopes. From the moment of formation of such a mineral, the process of radioactive decay of isotopes proceeds in it, accompanied by the accumulation of decay products. The decay of radioactive isotopes proceeds spontaneously, at a constant rate, independent of external factors; the number of radioactive isotopes decreases in accordance with the exponential law. Taking into account the constancy of the decay rate, to determine the age, it is sufficient to establish the amount of the radioactive isotope remaining in the mineral and the amount of the stable isotope formed during its decay. This relationship is described the main equation of geochronology:

Many radioactive isotopes are used to determine the age: 238 U, 235 U, 40 K, 87 Rb, 147 Sm, etc. etc. The results of determining the age of geological objects are expressed in 106 and 109 years, or in the values ​​of the International System of Units (SI): Ma and Ga. This abbreviation means, respectively, "million. years” and “billion years” ( from lat. Mega anna - million years, Giga anna - billion years).

Consider age determination by rubidium-strontium isochron method. As a result of the decay of the radioactive isotope 87 Rb, a non-radioactive decay product is formed - 87 Sr, the decay constant is 1.42 * 10 -11 years -1. The application of the isochron method involves the analysis of several samples taken from the same geological object, which increases the accuracy of age determination and allows the calculation of the initial isotopic composition of strontium (used to determine the formation conditions of the rock).

In the course of laboratory studies, the contents of 87 Rb and 87 Sr are determined, while the content of the latter is the sum of strontium initially contained in the mineral (87 Sr) 0 and strontium that arose during the radioactive decay of 87 Rb during the period of the mineral's existence:

In practice, not the abundances of these isotopes are measured, but their ratios to the stable 86Sr isotope, which gives more accurate results. As a result, the equation takes the form

The resulting equation has two unknowns: the time t and the initial ratio of strontium isotopes. To solve the problem, several samples are analyzed, the results are plotted as points on a graph in the coordinates 87 Sr/ 86 Sr – 87 Rb/ 86 Sr. In the case of correctly selected samples, all points lie along one straight line - isochrones (hence, they have the same age). The age of the analyzed samples is calculated from the isochron slope, and the initial strontium ratio is determined from the intersection of the 87 Sr/86 Sr isochron axis.

If the points on the graph do not lie on one line, we can talk about incorrect sampling. To avoid this, the following main conditions must be observed:

• samples must be taken from the same geological object (i.e. must be known to be of the same age);
• in ai the rocks to be followed should show no evidence of superimposed transformations that could lead to redistribution of isotopes;
• samples must have the same isotopic composition of strontium at the time of occurrence (it is unacceptable to use different rocks when constructing one isochrone).

Without dwelling on methods for determining age by other methods, we note only the features of some of them.

Currently, the most accurate is samarium - neodymium method, accepted as a standard against which the data of other methods are compared. It's connected about the fact that, due to geochemical features, these elements are the least affected by superimposed processes, often significantly about distorting or nullifying the results of age determinations. The method is based on the decay of the 147 Sm isotope with the formation of 144 Nd as the final decay product.

The potassium-argon method is based on the decay of the radioactive isotope 40 K. This method has long been widely used to determine the age of all genetic types of rocks. It is most effective in determining the time of formation of sedimentary rocks and minerals, such as glauconite. When applied to igneous and especially metamorphic rocks affected by superimposed alterations, this method often gives "rejuvenated" dates due to the loss of mobile argon.

radiocarbon method is based on the decay of the isotope 14 C, which is formed in the upper atmosphere as a result of the impact of cosmic radiation on atmospheric gases (nitrogen, argon, oxygen). Subsequently, 14 C, like a non-radioactive carbon isotope, forms carbon dioxide CO 2, and in its composition is involved in photosynthesis, thus being in the composition of plants and, further, the food chain is transferred to animals. 14 C enters the hydrosphere as a result of the exchange of CO 2 between the atmosphere and the World Ocean, then it ends up in the bones and carbonate shells of aquatic life. Intensive mixing of air masses in the atmosphere and the active participation of carbon in the global cycle of chemical elements leads to equalization of 14 C concentrations in the atmosphere, hydrosphere and biosphere. For living organisms, the equilibrium state is reached at the specific activity of 14 C, which is 13.56 ± 0.07 decays per minute per 1 gram of carbon. If the organism dies, then the supply of 14C stops; as a result of radioactive decay (transition to non-radioactive 14 N), the specific activity of 14 C decreases. By measuring the activity value in the sample and comparing it with the specific activity value in living tissue, it is easy to calculate the time of termination of the organism's vital activity using the formula

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Radiocarbon dating makes it possible to determine the age of samples containing carbon (bones, teeth, shells, wood, coal, etc.) up to 70 thousand years old. This determines its use in Quaternary geology and, especially, in archeology.

In conclusion of the consideration of the methods of isotope geology, it should be noted that, despite obtaining “absolute” dates expressed in years, we are dealing with model age- the results obtained inevitably contain some error and, moreover, the duration of the astronomical year has changed in the course of a long geological history.

Another group of methods of absolute geochronology is represented by seasonal and climatic methods. An example of such a method is varvochronology- the method of absolute geochronology, based on the calculation of annual layers in the "ribbon" deposits of glacial lakes. For near-glacial lakes, the characteristic deposits are the so-called "ribbon clays" - clearly layered sediments, consisting of a large number of parallel ribbons. Each belt is the result of a yearly cycle of sedimentation in lakes that are frozen for most of the year. It always consists of two layers. The upper - winter - layer is represented by dark clays (due to enrichment with organic matter), formed under the ice cover; the lower one, the summer one, is composed of coarser-grained light-colored sediments (mainly fine sands or silty-clay deposits) formed due to the material brought into the lake by glacial melt waters. Each pair of such puffs corresponds to 1 year.

Studying the rhythm of banded clays makes it possible not only to determine the absolute age, but also to correlate the sections located not far from each other, comparing the thicknesses of the layers.

The calculation of annual layers in the sediments of salt lakes is based on a similar principle, where in summer, due to increased evaporation, active precipitation of salts occurs.

The disadvantages of seasonal-climatic methods include their non-universality.

Periodization of geological history. Stratigraphic and geochronological scales

In terms of the category of relative time, it is necessary to have a universal scale for the periodization of history. So, in relation to the history of mankind, we use the expressions “before our era”, “in the Renaissance”, “in the XX century”, etc., referring any event or object of material culture to a certain time interval. A similar approach has been adopted in geology; for these purposes, the International Geochronological Scale and the International Stratigraphic Scale have been developed.

The main information about the geological history of the Earth is carried by layers of rocks, in which, as on the pages of a stone chronicle, the changes that took place on the planet and the evolution of the organic world are imprinted (the latter is “imprinted” in fossil complexes contained in layers of different ages). Layers of rocks that occupy a certain position in the general sequence of strata and are distinguished on the basis of their inherent features (more often - a complex of fossils) are stratigraphic units. The rocks that make up the stratigraphic units were formed over a certain interval of geological time, and, therefore, reflect the evolution of the earth's crust and the organic world over this period of time.

- a scale showing the sequence and subordination of the stratigraphic units that make up the earth's crust and reflect the stages of historical development passed by the earth. The object of the stratigraphic scale is the layers of rocks. The basis of the modern stratigraphic scale was developed in the first half of the 19th century and was adopted in 1881 at the II session of the International Geological Congress in Bologna. Later, the stratigraphic scale was supplemented by the geochronological scale.

Geological scale- a scale of relative geological time, showing the sequence and subordination of the main stages of the geological history of the Earth and the development of life on it. The object of the geochronological scale is geological time.

The geologic time scale (or geochronometric scale) is a sequential series of datings of the lower boundaries of common stratigraphic units, expressed in units of time (more often in millions of years) and calculated using absolute dating methods.

The object of the geochronological scale is the geochronological subdivisions - the intervals of geological time during which the rocks that are part of this stratigraphic subdivision were formed.

All stratigraphic units correspond to units of the geochronological scale.

At the same time, almost all stratigraphic units of the eonoteme-system rank have common, generally accepted international names.

The largest stratigraphic units are acrothemes and eonotemes. The Archean and Proterozoic acrothemes are combined under the name "Precambrian" (i.e., rock strata accumulated before the Cambrian period - the first period of the Phanerozoic) or "cryptozoic". The boundary of the Precambrian and Phanerozoic is the appearance in the layers of rocks of the remains of skeletal organisms. In the Precambrian, organic remains are rare, since soft tissues are quickly destroyed before they can be buried. The term "cryptozoic" itself was formed by merging the roots of words "cryptos" - hidden and "zoe" - life. When dividing the Precambrian strata into fractional stratigraphic units, the methods of isotopic geochronology play an important role, since organic remains are rare or absent at all, are difficult to determine and, most importantly, are not subject to rapid evolution (similar microfauna complexes remain unchanged over huge time intervals, which does not allow dismembering thickness on this basis).

Eonotems include eratems. Eratema, or Group- deposits formed during era; the duration of eras in the Phanerozoic is the first hundreds of millions of years. Eratems reflect major stages in the development of the Earth and the organic world. The boundaries between eratems correspond to turning points in the history of the development of the organic world. In the Phanerozoic, three erathems are distinguished: Paleozoic, Mesozoic and Cenozoic.

Eratems, in turn, include systems in their composition. System are deposits formed during period; the duration of the periods is tens of millions of years. One system differs from another by complexes of fauna and flora at the level of superfamilies, families and genera. In the Phanerozoic, 12 systems are distinguished: Cambrian, Ordovician, Silurian, Devonian, Carboniferous (Carboniferous), Permian, Triassic, Jurassic, Cretaceous, Paleogene, Neogene and Quaternary (Anthropogenic). The names of most systems come from the geographical names of the localities where they were first established. For each system on geological maps, a certain color is accepted, which is international, and an index formed by the initial letter of the Latin name of the system.

The Department- part of the system corresponding to deposits formed during one era; the duration of epochs is usually the first tens of millions of years. Differences between divisions are manifested in the difference between fauna and flora at the level of genera or groups. The names of departments are given according to their position in the system: lower, middle, upper, or only lower and upper; eras are respectively called early, middle, late.

The division is divided into tiers. Tier- deposits formed during century; centuries are several million years long.

Along with the main divisions of the stratigraphic and geochronological scales, regional and local divisions are used.

To regional stratigraphic units include horizon and lona.

Horizon- the main regional subdivision of the stratigraphic scale, uniting deposits of the same age, characterized by a certain complex of lithological and paleontological features. The horizons are given geographic names corresponding to the places where they are best represented and studied. The geochronological equivalent is time. For example, the Khaprovsky horizon, common on the coast of the Taganrog Bay of the Sea of ​​Azov, corresponds to the thickness of river sands that formed at the end of the Neogene period. The stratotype (the most representative section of the stratigraphic horizon, which is its standard) of this horizon is located near st. Khapry. Let us add that the term “horizon”, used without a geographical name, is understood as a layer or pack of layers identified on the basis of some features (paleontological or lithological), that is, it is a designation for free use.

Lona is part of the horizon distinguished by the complex of fauna and flora characteristic of the given region, and reflects a certain phase in the development of the organic world of the given region. The name of the womb is given according to the type-index. The geochronological equivalent of the womb is time.

Local stratigraphic units are rock strata distinguished by a number of features, mainly by lithological or petrographic composition.

Complex- the largest local stratigraphic unit. The complex has a very large thickness, a complex composition of rocks formed during some major stage in the development of the territory. The complex is assigned a geographical name according to the characteristic place of its development. Most often, the complexes are distinguished during the dismemberment of metamorphic strata.

Series covers a fairly thick and complex rock mass for which there are some common features: similar formation conditions, the predominance of certain types of rocks, a close degree of deformation and metamorphism, etc. Series usually correspond to a single major cycle of development of the territory.

Basic unit of local stratigraphic units is a retinue. Retinue is a stratum of rocks formed in a certain physical and geographical setting and occupying a certain stratigraphic position in the section. The main features of the suite are the presence of stable lithological features throughout the entire area of ​​its distribution and a clear expression of boundaries. The formation gets its name from the geographical location of the stratotype.

The boundaries of local stratigraphic units often do not coincide with the boundaries of units of a single stratigraphic scale.

In the course of work, a geologist often has to use also auxiliary stratigraphic units- thickness, pack, layer, deposit, etc., usually named according to characteristic rocks, color, lithological features or characteristic organic remains (limestone sequences, layers with Matra fabriana, etc.).

Stratigraphic (g geochronological) scale is the scale of geological time, the stages of which are identified by paleontology for the development of life on Earth.

The two names of this scale have different meanings: the stratigraphic scale is used to describe the sequence and relationships of rocks that make up the earth's crust, and the geochronological one - to describe geological time. These scales differ in terminology, you can see the differences in the table below:

General stratigraphic divisions (stratons)	Subdivisions geochronological scale
Akrotema	Akron
Eonoteme	Aeon
Eratema	Era
System	Period
The Department	Epoch
Tier	Century

Thus, we can say that, for example, the limestone stratum belongs to the Cretaceous system, but limestones formed in the Cretaceous period.

Systems, departments, tiers can be upper or lower, and periods, epochs and centuries - early or late.

These terms should not be confused.

Phanerozoic

Phanerozoic the eon includes three eras, the names of which should be known to many: Paleozoic(era of ancient life), mesozoic(era of middle life) and Cenozoic(era of new life). Eras are further divided into periods. Paleozoic: Cambrian, Ordovician, Silurian, Devonian, Carboniferous, Permian; Mesozoic: Triassic, Jurassic, Cretaceous; Cenozoic: Paleogene, Neogene and Quaternary. Each period has its own letter designation and its own color for marking on geological maps.

Remembering the order of the periods is quite simple using a mnemonic device. The first letter of each word in the following two sentences corresponds to the first letter of the period:

To every O educated With student D must To smoke P apyros. T s, YU rchik, M al, P go away H ID H inarik.

	Symbol	Colour
Cambrian	€	bluish green
Ordovician	O	Olive
Silurus	S	Grey-green
Devonian	D	Brown
Carbon	C	Grey
Permian	P	tan
Triassic	T	Violet
Yura	J	Blue
Chalk	K	light green
Paleogene	P*	Orange
Neogene	N	Yellow
Quaternary	Q	yellowish gray

*Paleogene symbol may not be displayed as not found in all fonts: this is a ruble symbol (P with a horizontal bar)

Precambrian

Archaean and Proterozoic The Akrons are older subdivisions, and they account for most of our planet's existence. If the Phanerozoic lasted about 530 million years, then only the Proterozoic - more than one and a half billion years.

Life on Earth originated over 3.5 billion years ago, immediately after the completion of the formation of the earth's crust. Throughout time, the emergence and development of living organisms influenced the formation of relief and climate. Also, tectonic and climatic changes that have taken place over the years have influenced the development of life on Earth.

A table of the development of life on Earth can be compiled based on the chronology of events. The entire history of the Earth can be divided into certain stages. The largest of them are the eras of life. They are divided into eras, eras - into - into eras, eras - into centuries.

Ages of life on earth

The entire period of the existence of life on Earth can be divided into 2 periods: the Precambrian, or Cryptozoic (primary period, 3.6 to 0.6 billion years), and Phanerozoic.

Cryptozoic includes the Archean (ancient life) and Proterozoic (primary life) eras.

Phanerozoic includes the Paleozoic (ancient life), Mesozoic (middle life) and Cenozoic (new life) eras.

These 2 periods of development of life are usually divided into smaller ones - eras. The boundaries between eras are global evolutionary events, extinctions. In turn, eras are divided into periods, periods - into epochs. The history of the development of life on Earth is directly related to changes in the earth's crust and the planet's climate.

Era of development, countdown

It is customary to single out the most significant events in special time intervals - eras. Time is counted backwards, from ancient life to the new. There are 5 eras:

1. Archean.
2. Proterozoic.
3. Paleozoic.
4. Mesozoic.
5. Cenozoic.

Periods of development of life on Earth

The Paleozoic, Mesozoic and Cenozoic eras include periods of development. These are smaller periods of time, compared to eras.

Palaeozoic:

• Cambrian (Cambrian).
• Ordovician.
• Silurian (Silur).
• Devonian (Devonian).
• Carboniferous (carbon).
• Perm (Perm).

Mesozoic era:

• Triassic (Triassic).
• Jura (Jurassic).
• Cretaceous (chalk).

Cenozoic era:

• Lower Tertiary (Paleogene).
• Upper Tertiary (Neogene).
• Quaternary, or anthropogen (human development).

The first 2 periods are included in the Tertiary period lasting 59 million years.

Table of the development of life on Earth

era, period	Duration	Live nature	Inanimate nature, climate
Archean era (ancient life)	3.5 billion years	The appearance of blue-green algae, photosynthesis. Heterotrophs	The predominance of land over the ocean, the minimum amount of oxygen in the atmosphere.
Proterozoic era (early life)	2.7 Ga	The appearance of worms, mollusks, the first chordates, soil formation.	The land is a stone desert. Accumulation of oxygen in the atmosphere.
The Paleozoic era includes 6 periods:
1. Cambrian (Cambrian)	535-490 Ma	development of living organisms.	Hot climate. The dry land is deserted.
2. Ordovician	490-443 Ma	The emergence of vertebrates.	Flooding of almost all platforms with water.
3. Silurian (Silur)	443-418 Ma	Exit of plants to land. Development of corals, trilobites.	with the formation of mountains. The seas prevail over the land. The climate is varied.
4. Devonian (Devonian)	418-360 Ma	The appearance of fungi, lobe-finned fish.	Formation of intermountain depressions. The predominance of a dry climate.
5. Carboniferous (carbon)	360-295 Ma	Appearance of the first amphibians.	The sinking of the continents with the flooding of territories and the emergence of swamps. The atmosphere contains a lot of oxygen and carbon dioxide.
6. Perm (Perm)	295-251 Ma	Extinction of trilobites and most amphibians. The beginning of the development of reptiles and insects.	Volcanic activity. Hot climate.
The Mesozoic era includes 3 periods:
1. Triassic (Triassic)	251-200 Ma	Gymnosperm development. The first mammals and bony fishes.	Volcanic activity. Warm and sharply continental climate.
2. Jurassic (Jurassic)	200-145 Ma	The emergence of angiosperms. The spread of reptiles, the appearance of the first bird.	Mild and warm climate.
3. Cretaceous (chalk)	145-60 Ma	The appearance of birds, higher mammals.	Warm climate followed by cooling.
The Cenozoic era includes 3 periods:
1. Lower Tertiary (Paleogene)	65-23 Ma	The flowering of angiosperms. The development of insects, the appearance of lemurs and primates.	Mild climate with the allocation of climatic zones.
2. Upper Tertiary (Neogene)	23-1.8 Ma	The emergence of ancient people.	Dry climate.
3. Quaternary or anthropogen (human development)	1.8-0 Ma	The appearance of man.	Cooling.

The development of living organisms

The table of the development of life on Earth involves the division not only into time intervals, but also into certain stages of the formation of living organisms, possible climatic changes (ice age, global warming).

• Archean era. The most significant changes in the evolution of living organisms are the appearance of blue-green algae - prokaryotes capable of reproduction and photosynthesis, the emergence of multicellular organisms. The appearance of living protein substances (heterotrophs) capable of absorbing organic substances dissolved in water. In the future, the appearance of these living organisms made it possible to divide the world into flora and fauna.

• Mesozoic era.

• Triassic. Distribution of plants (gymnosperms). An increase in the number of reptiles. The first mammals, bony fish.
• Jurassic period. The predominance of gymnosperms, the emergence of angiosperms. The appearance of the first bird, the flowering of cephalopods.
• Cretaceous period. Spread of angiosperms, reduction of other plant species. The development of bony fish, mammals and birds.

• Cenozoic era.
  • Lower Tertiary period (Paleogene). The flowering of angiosperms. The development of insects and mammals, the appearance of lemurs, later primates.
  • Upper Tertiary period (Neogene). The development of modern plants. The appearance of human ancestors.
  • Quaternary period (anthropogen). Formation of modern plants, animals. The appearance of man.

Development of conditions of inanimate nature, climate change

The table of the development of life on Earth cannot be presented without data on changes in inanimate nature. The emergence and development of life on Earth, new species of plants and animals, all this is accompanied by changes in inanimate nature and climate.

Climate Change: Archean Era

The history of the development of life on Earth began through the stage of the predominance of land over water resources. The relief was poorly outlined. The atmosphere is dominated by carbon dioxide, the amount of oxygen is minimal. Salinity is low in shallow water.

The Archean era is characterized by volcanic eruptions, lightning, black clouds. The rocks are rich in graphite.

Climatic changes during the Proterozoic era

Land is a stone desert, all living organisms live in water. Oxygen accumulates in the atmosphere.

Climate change: the Paleozoic era

During various periods of the Paleozoic era, the following occurred:

• Cambrian period. The land is still deserted. The climate is hot.
• Ordovician period. The most significant changes are the flooding of almost all northern platforms.
• Silurian. Tectonic changes, the conditions of inanimate nature are diverse. Mountain building occurs, the seas prevail over the land. Regions of different climates, including areas of cooling, were determined.
• Devonian. Dry climate prevails, continental. Formation of intermountain depressions.
• Carboniferous period. The sinking of the continents, wetlands. The climate is warm and humid, with a lot of oxygen and carbon dioxide in the atmosphere.
• Permian period. Hot climate, volcanic activity, mountain building, drying up of swamps.

In the Paleozoic era, mountains formed. Such changes in the relief affected the world's oceans - the sea basins were reduced, a significant land area was formed.

The Paleozoic era marked the beginning of almost all major deposits of oil and coal.

Climatic changes in the Mesozoic

The climate of different periods of the Mesozoic is characterized by the following features:

• Triassic. Volcanic activity, the climate is sharply continental, warm.
• Jurassic period. Mild and warm climate. The seas prevail over the land.
• Cretaceous period. Retreat of the seas from the land. The climate is warm, but at the end of the period, global warming is replaced by cooling.

In the Mesozoic era, the previously formed mountain systems are destroyed, the plains go under water (Western Siberia). In the second half of the era, the Cordilleras, the mountains of Eastern Siberia, Indochina, partly Tibet, formed the mountains of the Mesozoic folding. A hot and humid climate prevails, contributing to the formation of swamps and peat bogs.

Climate change - Cenozoic era

In the Cenozoic era, there was a general uplift of the Earth's surface. The climate has changed. Numerous glaciations of the earth covers advancing from the north have changed the appearance of the continents of the Northern Hemisphere. Due to such changes, hilly plains were formed.

• Lower Tertiary period. Mild climate. Division into 3 climatic zones. Formation of continents.
• Upper Tertiary period. Dry climate. The emergence of steppes, savannahs.
• Quaternary period. Multiple glaciation of the northern hemisphere. Climate cooling.

All changes during the development of life on Earth can be written in the form of a table that will reflect the most significant stages in the formation and development of the modern world. Despite the already known methods of research, even now scientists continue to study history, make new discoveries that allow modern society to find out how life developed on Earth before the appearance of man.

Students, graduate students, young scientists who use the knowledge base in their studies and work will be very grateful to you.

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abstract

Geological table of the Earth

Completed by: Mikhail Konyshev

Introduction

Geological 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 4.5-4.6 billion years. No rocks or minerals have been found on the surface of the Earth that could be witnesses to the formation of the planet. The maximum age of the Earth is limited by the age of the earliest solid formations in the solar system - refractory inclusions rich in calcium and aluminum (CAI) from carbonaceous chondrites. The age of the CAI from the Allende meteorite according to the results of modern studies of the U-Pb isotope method is 4568.5±0.5 Ma. This is the best estimate of the age of the solar system to date. The time of the formation of the Earth as a planet may be later than this date by millions and even many tens of millions of years.

Subsequent time in the history of the Earth 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.

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 (Vmends - the German name for the Slavic people of the Lusatian Sorbs), Ordovician and Silurian (tribes of the Celts Ordomviks and Silumrs) 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 period because of the widespread use of writing chalk.

The principle of constructing the scale

geochronological scale earth geology

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 (eons): Phanerozoic and Precambrian (Cryptose) according to the appearance of fossil remains in sedimentary rocks. Cryptozoic is a time of hidden life, in which only soft-bodied organisms existed, leaving no traces in sedimentary rocks. The Phanerozoic began with the appearance of many species of mollusks and other organisms on the border of the Ediacaran (Vendian) and Cambrian, 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.

Eon (eonoteme)	Era (erathema)	(system)		years ago	Main events
Phanerozoic	Cenozoic	Quaternary (Anthropogenic)			End of the Ice Age. Rise of civilizations
Pleistocene		Extinction of many large mammals. The emergence of modern man
Neogene
Paleogene	Oligocene	33.9 ± 0.1 million	Appearance of the first great apes.
	55.8 ± 0.2 million	The emergence of the first "modern" mammals.
Paleocene	65.5 ± 0.3 million
		145.5 ± 0.4 million	The first placental mammals. Dinosaur extinction.
	199.6 ± 0.6 million	The appearance of marsupial mammals and the first birds. Rise of the dinosaurs.
Triassic	251.0 ± 0.4 million	The first dinosaurs and egg-laying mammals.
Paleozoic	Permian	299.0 ± 0.8 million	About 95% of all existing species died out (Mass Permian extinction).
Coal	359.2 ± 2.8 million	The appearance of trees and reptiles.
Devonian	416.0 ± 2.5 million	The appearance of amphibians and spore plants.
Silurian	443.7 ± 1.5 million	Exit of life to land: scorpions; emergence of jawed
Ordovician	488.3 ± 1.7 million	Racoscorpions, the first vascular plants.
Cambrian	542.0 ± 1.0 million	The emergence of a large number of new groups of organisms ("Cambrian explosion").
Precambrian
Proterozoic	Neoproterozoic	Ediacaran		The first multicellular animals.
cryogeny		One of the largest glaciations on Earth
		Beginning of the disintegration of the supercontinent Rodinia
Mesoproterozoic			Supercontinent Rodinia, superocean Mirovia
		First multicellular plants (red algae)
Paleoproterozoic	Statery
Orosirium
		Oxygen catastrophe
	neoarchean
Mesoarchean
paleoarchaean
		The emergence of primitive unicellular organisms
catarchean		~4.6 billion years ago - the formation of the Earth.

Scale charts of the geochronological scale

Three chronograms are presented, reflecting different stages of the history of the earth on a different scale.

1. The top diagram covers the entire history of the earth;

2. The second - Phanerozoic, the time of the mass appearance of various forms of life;

3. Lower - Cenozoic, the period of time after the extinction of the dinosaurs.

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Age of rocks and methods for their determination

The concept of geological time. Degeological and geological stages of the Earth's development. Age of sedimentary rocks. Periodization of the history of the Earth. General geochronological and stratigraphic scales. Methods for determining the isotopic age of rocks.

abstract, added 06/16/2013

Physical and geological processes

The internal structure of the Earth. The concept of the mantle as the geosphere of the Earth, which surrounds the core. The chemical composition of the Earth. The layer of low viscosity in the upper mantle of the Earth (asthenosphere), its role and significance. Earth's magnetic field. Features of the atmosphere and hydrosphere.

presentation, added 11/21/2016

The main characteristics of the planet

Modern ideas about the internal structure of the Earth. Radius of a heliocentric orbit. Experimental data on the structure of the globe. Earth's crust and geological chronology. Features of the geochronological scale. Processes that form the earth's crust.

abstract, added 11/11/2009

Evolutionary changes in the Earth's atmosphere

Features of the composition and structure of the Earth's atmosphere. The evolution of the earth's atmosphere, the process of its formation over the centuries. The appearance of the aquatic environment as the beginning of the geological history of the Earth. The content and origin of impurities in the atmosphere, their chemical composition.

abstract, added 11/19/2009

Paleomagnetic scale of reversals of the Earth's main magnetic field and the age of the ocean floor

Magnetization of linear sections of the oceanic crust during reversals of the main magnetic field, expansion and buildup of oceanic plates in rift zones. Drawing up a geochronological scale of paleomagnetic anomalies in the process of marine magnetic surveys.

abstract, added 08/07/2011

Characteristics of the main shells of the Earth

The main shells of the Earth: atmosphere, hydrosphere, biosphere, lithosphere, pyrosphere and centrosphere. The composition of the Earth and its physical structure. Geothermal regime of the Earth and its specificity. Exogenous and endogenous processes and their influence on the solid surface of the planet.

abstract, added 02/08/2011

Methods of historical geology and the structure of the earth's crust

The concept and tasks of historical geology. Paleontological and non-paleontological methods for reconstructing the geological past. Determination of the relative age of igneous rocks. Periodization of the history of the Earth. The concept of stratigraphic units.

abstract, added 05/24/2010

Modern mineralogical models of the Earth's mantle

Model of the structure of the Earth. The work of the Australian seismologist K.E. Bullen. The composition of the upper mantle and the mantle below the boundary of 670 km. The modern structure of the Earth. Examples of the distribution of velocity anomalies in the mantle according to seismic tomography data at different depths.

presentation, added 04/20/2017

The internal structure of the Earth

The formation of the Earth according to modern cosmological concepts. Structure model, basic properties and their parameters characterizing all parts of the Earth. The structure and thickness of the continental, oceanic, subcontinental and suboceanic crust.

abstract, added 04/22/2010

The internal structure of the Earth

The creation of a model of the internal structure of the Earth as one of the greatest achievements of science in the 20th century. Chemical composition and structure of the earth's crust. Characteristics of the composition of the mantle. Modern ideas about the internal structure of the Earth. Composition of the Earth's core.

abstract, added 03/17/2010

GEOLOGICAL CHRONOLOGY

A very important characteristic of rocks is their age. As shown above, many properties of rocks, including engineering-geological ones, depend on it. In addition, on the basis of studying, first of all, the age of rocks, historical geology recreates the patterns of development and formation of the earth's crust. An important section of historical geology is geochronology - the science of the sequence of geological events in time, their duration and subordination, which it establishes by determining the age of rocks based on the use of various methods and geological disciplines. The relative and absolute age of rocks is distinguished.

In assessing relative age, older and younger rocks are distinguished by highlighting the time of an event in the history of the Earth in relation to the time of another geological event. Relative age is easier to determine for sedimentary rocks in their undisturbed (close to horizontal occurrence) occurrence, as well as for volcanic and less often metamorphic rocks interbedded with them.

The stratigraphic (stratum - layer) method is based on the study of the sequence of occurrence and the relationship of layers of sedimentary deposits, based on the principle of superposition: each overlying layer is younger than the lower one.

It is used for strata with undisturbed horizontal occurrence of layers (Fig. 22). This method should be carefully applied when the layers are folded; first, their tops and bottoms must be determined. Young is the layer 3 , and the layers 1 and 2 - more ancient.

Lithologo — petrographic method is based on the study of the composition and structure of rocks in adjacent sections of wells and the identification of rocks of the same age - correlation of sections . Sedimentary, volcanic and metamorphic rocks of the same facies and age, such as clays or limestones, basalts or marbles, will have similar textural and structural features and composition.

Geological time scale for the history of life on Earth

Older rocks tend to be more altered and compacted, while younger ones are slightly altered and porous. It is more difficult to use this method for thin continental deposits, the lithological composition of which is rapidly changing along the strike.

The most important method for determining relative age is paleontological ( biostratigraphic ) method , based on the allocation of layers containing various complexes of fossil remains of extinct organisms. The method is based on the principle of evolution : life on Earth develops from simple to complex and does not repeat itself in its development. The science that establishes the pattern of development of life on Earth by studying the remains of fossil animals and plant organisms - fossils ( fossils) contained in the strata of sedimentary rocks is called paleontology. The time of formation of one or another rock corresponds to the time of death of organisms, the remains of which were buried under the layers above the accumulated sediments. The paleontological method makes it possible to determine the age of sedimentary rocks in relation to each other, regardless of the nature of the occurrence of layers, and to compare the age of rocks occurring in distant parts of the earth's crust. Each segment of geological time corresponds to a certain composition of life forms or guiding organisms (Fig. 23–29). Leading fossils ( forms ) lived for a short period of geological time on vast areas, as a rule, in reservoirs, seas and oceans. Starting from the second half of the twentieth century. began to actively apply the micropaleontological method, including spore — pollen, to study organisms invisible to the eye. On the basis of the paleontological method, schemes of the evolutionary development of the organic world were drawn up.

Thus, based on the above methods for determining the relative age of rocks by the end of the 19th century. a geochronological table was compiled, which includes subdivisions of two scales: stratigraphic and corresponding geochronological.

Stratigraphic subdivision (unit) - a set of rocks that make up a certain unity in terms of a set of features (features of the material composition, organic remains, etc.), which allows you to distinguish it in the section and trace about the area. Each stratigraphic unit reflects the peculiarity of the natural geological stage of the development of the Earth (or a separate area), expresses a certain geological age and is comparable to a geochronological unit.

Geochronological (geohistorical) scale - a hierarchical system of geochronological (temporal) divisions, equivalent to units of the general stratigraphic scale. Their ratio and subdivision is shown in Table. fifteen.

isolated in the UK, Perm - in Russia, etc. (Table 16).

Absolute age - the duration of the existence (life) of the breed, expressed in years - in time intervals equal to the modern astronomical year (in astronomical units). It is based on measuring the content of radioactive isotopes in minerals: 238U, 232Th, 40K, 87Rb, 14C, etc., their decay products and knowledge of the experimentally revealed decay rate. The latter has a half-life – the time it takes for half of the atoms of a given unstable isotope to decay. The half-life varies greatly for different isotopes (Table 17) and determines the possibilities of its application.

Methods for determining the absolute age got their name from the products of radioactive decay, namely: lead (uranium-lead), argon (potassium-argon), strontium (rubidium-strontium), etc. The most commonly used potassium-argon method, since the 40K isotope contained in many minerals (mica, amphiboles, feldspars, clay minerals), decomposes with the formation of 40Ar and has a half-life of 1.25 billion years. Calculations made using this method are often verified by the strontium method. In these minerals, potassium is isomorphically replaced by 87Rb, which, upon decay, transforms into the 87Sr isotope. With the help of 14C, the age of the youngest Quaternary breeds is determined. Knowing how much lead is formed from 1 g of uranium per year, determining their combined content in a given mineral, one can find the absolute age of the mineral and the rock in which it is located.

The use of these methods is complicated by the fact that rocks during their "life" experience various events: magmatism, metamorphism, and weathering, during which the minerals "open", change and lose the isotopes and decay products partially contained in them.

Therefore, the term "absolute" age used is convenient to use, but is not absolutely accurate for the age of rocks. It is more correct to use the term "isotopic" age. A systematic correlation is made between the subdivisions of the relative geochronological table and the absolute age of the rocks, which is still being refined and given in the tables.

Geologists, builders and other professionals can obtain information about the age of rocks by studying geological maps or related geological reports. On the maps, the age of rocks is shown by the letter and color that are accepted for the corresponding subdivision of the geochronological table. Comparing the relative age of specific rocks shown by letter and color with the absolute age of the unified geochronological table, we can assume the absolute age of the studied rocks. Civil engineers must have an understanding of the age of rocks and its designation, and also use them when reading geological documentation (maps and sections) compiled when designing buildings and structures.

Of particular interest is the Quaternary period (Table 18). The deposits of the Quaternary system cover the entire earth's surface with a continuous cover, their strata contain the remains of an ancient man and his household items. In these sequences, various deposits (facies) alternate and replace each other in area: eluvial, alluvial , moraine and fluvioglacial, lacustrine — marsh. Deposits of alluvial gold and other valuable metals are confined to alluvium. Many breeds of the Quaternary system are raw materials for the production of building materials. A large place is occupied by deposits of the cultural layer , resulting from human activity. They are distinguished by considerable friability and great heterogeneity. Its presence can complicate the construction of buildings and structures.

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. 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.

New geological period

The International Stratigraphic Committee (ISC) decided at the end of 2000 - consider the time since the second quarter of 2001 as a new geological period as part of the Cenozoic era. In this regard, we have already begun to receive questions to the editorial office:

Why is this needed?

Why was the Quaternary period so short - only 1-2 million years (according to various estimates), while all previous periods lasted tens of millions of years?

What will be the name and designation of the period? (Those who read about the proposed period name ask for an explanation.)

Why exactly from the second quarter, and not from the beginning of some year?

We will try to answer these questions.

IN AND. Vernadsky believed that human activity becomes a powerful geological factor, commensurate with natural factors. The validity of this became especially evident towards the end of the 20th century. The movement of huge masses of rock during mining, artificial intervention in the geochemical and hydrogeological regimes of the earth's crust required a strict account of all this impact. Therefore, the MSC decided to record the state of the earth's crust at some point in order to keep a record of its changes as a result of technogenic impact starting from that moment. It would be logical to make this moment the beginning of 2000 or 2001, but by the beginning of 2000 they did not have time to get a clear picture of the state of the interior of the planet as a whole, and by September 2000 it turned out that the necessary documentation did not have time even by the beginning of 2001. That's the start of the second quarter.

Analyzing the geochronological table, you immediately notice that the duration of eras and periods gradually decreases as we approach the present. They wrote about the general acceleration of geological processes, but most likely this is due to the fact that we know more about later geological periods, more traces of them remain, so periodization can be done with greater fractionality. As for the most recent time, human intervention has indeed accelerated many processes.

Earlier in geology, igneous and metamorphic rocks were considered primary, sedimentary - secondary. When in the middle of the XVIII century. younger sedimentary rocks were isolated, they were called tertiary, they included the Paleogene and Neogene, which from half a century ago constituted a single tertiary system, which was formed during the eponymous tertiary period. In 1829, the "youngest" deposits were identified, they were called Quaternary; accordingly, the Quaternary period was also singled out; its second name is anthropogen, in Greek man-bearing.

Geological scale

Therefore, the MSC did not suffer for a long time with the name of the new period: without further ado, the period was called fivefold, or technogenic(however, here the connotation is somewhat different: not “giving birth to technology”, but “born by technology”). The Quaternary period is denoted by the symbol Q (Latin quartus- fourth). Fivefold wanted to be called by analogy quintus(fifth), but they realized it in time: they would have to designate it with the same letter Q, only, probably, crossed out, like the crossed out P - this is the Paleogene (not to be confused with the Permian), the crossed out C - the Cambrian (unlike the Carboniferous); everyone who has typed these characters on a typewriter, and especially on a computer, knows how inconvenient it is. We decided to take as a basis not Latin, but English or German and designate the period F ( five or fu..nf), there is a blessing and a precedent: the Cretaceous period is denoted by the letter K from the German Kreide- a piece of chalk.

Now all states are obliged to submit to the MSC every 5 years a report on the volume of mining operations, on which rocks, in what quantity, and from where they were moved, where they formed strata of fivefold, or technogenic, deposits. In Russian terminology, that's right - technogenic. The deposits and landforms formed by man are called anthropogenic, and the deposits and forms formed by any processes during the Quaternary period, or the Anthropogen, are called Anthropogenic. Hence it follows that the rocks formed in the fivefold period in a natural way, without human intervention, can also be called technogenic.

In a word, a very serious decision has been made. How effective will be its results, time will tell.

The longest geological period on the planet

Approximately 2500 million years ago, the Archaean was replaced by a new eon - the Proterozoic. And it was he who subsequently became the longest geological period in the history of our planet, lasting almost 2000 million years and including three long eras: Paleoproterozoic, Mesoproterozoic and Neoproterozoic, during which significant changes took place on Earth.

Dividing the history of the Earth into eras and periods

And the first significant event that occurred at the beginning of the longest geological period on the planet, or rather in the era of the Paleoproterozoic, the siderian period, that is, about 2.4 billion years ago, is, of course, an oxygen catastrophe, which entailed significant changes in the composition of the atmosphere . So, it was in the earliest geological period of the Proterozoic, due to the extinction of the activity of oceanic and terrestrial volcanoes, that the biochemical composition of the world ocean began to change completely, as a result of which oxygen, released by already existing cyanobacteria, began to be produced even more rapidly, leaving local pockets and oxidizing all around. Upon completion of the oxidation process, the atmosphere finally began to be enriched with free oxygen, and it was this factor that led to a cardinal change in the composition of the atmosphere. It is noteworthy that there is no exact data on its original composition, and the fact that everything changed after the oxygen catastrophe is evidenced by the found ancient rocks that have not undergone oxidation processes.

After these events, the world was literally “turned inside out”, because if earlier it was filled with anaerobic microorganisms that could exist exclusively outside the oxygen environment, pushing aerobic microorganisms into local pockets, then a gradual increase in the level of oxygen in the atmosphere led to the opposite picture. However, this does not mean at all that the rapidly changing atmosphere even remotely resembled the modern one, because only 400 million years after the start of the oxygen catastrophe, the content of free oxygen in its composition reached ten percent of the volume of O2 that can be observed today (this milestone was called the point Pasteur). It is noteworthy that it was previously believed that this figure was exactly 10 times less, however, as it turned out later, both figures were quite enough to ensure the full functioning of rapidly multiplying unicellular organisms. Nevertheless, these processes entailed another colossal test for the planet - the Ice Age, which developed as a result of the massive absorption of methane by rapidly released free oxygen.

And although at that time the luminosity of the Sun for our planet increased on average by as much as 6 percent, it could not warm up due to a shortage of methane, which is capable of producing a powerful greenhouse effect, according to one theory, ice covered the entire globe at that time, literally turning it into a giant snowball. It is noteworthy that by that period the volume of the world ocean that exists in modern times had already formed, and after the end of the Huron glaciation period, which occurred approximately 2.1 billion years ago, more complex organisms in the form of sponges and fungi began to appear on Earth.

In addition, the soil began to actively form, the main role in this process was played by the vital activity of bacteria and unicellular algae, now known as prokaryotes. Another significant event in this era of the Earth's existence was the first relative stabilization of the continents, as a result of which the once-existing super-continent Rodinia began to form, although it was far from the only one in its entire history. The end of the formation of this formation is approximately dated to 1150 million years BC, but by the end of the Proterozoic it again disintegrated.

In fact, Rodinia existed for no more than 250 million years, and after the collapse, about 8 large fragments remained from it, which later became the basis for modern continents. During this period, complex organisms already existed on the planet, as evidenced by their numerous remains. Unfortunately, the collapse of the super-continent was not the last test for the Earth of the Paleozoic era, because soon its surface was again covered with ice, which claimed hundreds of thousands of lives of animals that had appeared by that time.

It is noteworthy that the found remains of animals, most likely dead from another global cooling, had a solid skeleton. This fact indicates that evolution during the Proterozoic period was striking in the scale of its development.

The history of the development of the Earth for the convenience of study is divided into four eras and eleven periods. The two most recent periods are in turn divided into seven systems or eras.

The earth's crust is stratified, i.e. the various rocks that make it up lie on top of each other in layers. As a rule, the age of rocks decreases towards the upper layers. The exception is the areas with disturbed due to the movements of the earth's crust, the occurrence of layers. William Smith in the 18th century noticed that during the geological periods of time, some organisms have significantly advanced in their structure.

According to modern estimates, the age of the planet Earth is approximately 4.6 - 4.9 10 years. These estimates are based mainly on the study of rocks by radiometric dating methods.

ARCHEUS. Not much is known about life in the Archean. The only animal organisms were cellular prokaryotes - bacteria and blue-green algae. The products of the vital activity of these primitive microorganisms are also the most ancient sedimentary rocks (stromatolites) - calcareous formations in the form of pillars, found in Canada, Australia, Africa, the Urals, and Siberia. Sedimentary rocks of iron, nickel, manganese have a bacterial basis. Many microorganisms are active participants in the formation of colossal, as yet little explored mineral resources at the bottom of the World Ocean. The role of microorganisms is also great in the formation of oil shale, oil and gas.

Geological table of the Earth

Blue-green, bacteria quickly spread in the Archaean and become the masters of the planet. These organisms did not have a separate nucleus, but a developed metabolic system, the ability to reproduce. Blue-green, in addition, possessed the apparatus of photosynthesis. The appearance of the latter was the largest aromorphosis in the evolution of living nature and opened one of the ways (probably specifically terrestrial) for the formation of free oxygen.

By the end of the Archean (2.8-3 billion years ago), the first colonial algae appeared, the fossilized remains of which were found in Australia, Africa, etc.

The most important stage in the development of life on Earth is closely related to the change in the concentration of oxygen in the atmosphere, the formation of the ozone screen. Thanks to the vital activity of blue-greens, the content of free oxygen in the atmosphere has increased markedly. The accumulation of oxygen led to the emergence of a primary ozone screen in the upper layers of the biosphere, which opened horizons for flourishing.

PROTEROZOI. The Proterozoic is a huge stage in the historical development of the Earth. During its course, bacteria and algae reach an exceptional flowering, with their participation, the processes of sedimentation were intensively going on. As a result of the vital activity of iron bacteria in the Proterozoic, the largest iron ore deposits were formed.

At the turn of the early and middle Riphean, the dominance of prokaryotes is replaced by the flourishing of eukaryotes - green and golden algae. From unicellular eukaryotes, multicellular ones with a complex organization and specialization develop in a short time. The oldest representatives of multicellular animals have been known since the late Riphean (700-600 million years ago).

Now we can state that 650 million years ago, the Earth's seas were inhabited by a variety of multicellular organisms: solitary and colonial polyps, jellyfish, flatworms, and even the ancestors of modern annelids, arthropods, molluscs, and echinoderms. Some forms of fossil animals are now difficult to assign to known classes and types. Among plant organisms at that time, unicellular organisms predominated, but multicellular algae (green, brown, red), fungi also appear.

PALEOZOIC. By the beginning of the Paleozoic era, life had passed perhaps the most important and difficult part of its journey. Four kingdoms of living nature were formed: prokaryotes, or pellets, mushrooms, green plants, animals.

The ancestors of the kingdom of green plants were unicellular green algae, common in the seas of the Proterozoic. Along with floating forms among the bottoms, there appeared those attached to the bottom. A fixed lifestyle required the dismemberment of the body into parts. But the acquisition of multicellularity, the division of a multicellular body into parts that perform various functions, turned out to be more promising.

Of decisive importance for further evolution was the emergence of such an important aromorphosis as the sexual process.

How and when did the division of the living world into plants and animals occur? Do they have the same root? Disputes of scientists around this issue do not subside even today. Perhaps the first animals evolved from a common stem of all eukaryotes or from single-celled green algae.

CAMBRIAN- flowering of skeletal invertebrates. During this period, another period of mountain building took place, the redistribution of land and sea area.

The climate of the Cambrian was temperate, the continents were unchanged. Only bacteria and blue-greens still lived on land. The seas were dominated by green and brown algae attached to the bottom; diatoms, golden algae, and euglena algae swam in the water column.

As a result of the increase in the washout of salts from the land, marine animals have been able to absorb mineral salts in large quantities. And this, in turn, opened up wide ways for them to build a rigid skeleton.

The oldest arthropods - trilobites, outwardly similar to modern crustaceans - wood lice, have reached the widest distribution.

Very characteristic of the Cambrian is a peculiar type of multicellular animals - the archaeocyath, which died out by the end of the period. A variety of sponges, corals, brachiopods, and mollusks also lived at that time. Later, sea urchins appeared.

ORDOVIC. In the seas of the Ordovician, green, brown and red algae, numerous trilobites were diversely represented. In the Ordovician, the first cephalopods, relatives of modern octopuses and squids, appeared, brachiopods, gastropods spread. There was an intensive process of formation of reefs by four-beam corals and tabulates. Graptolites are widely used - hemichordates, combining the features of invertebrates and vertebrates resembling modern lancelets.

In the Ordovician, spore plants appeared - psilophytes, growing along the banks of fresh water bodies.

SILUR. The warm shallow seas of the Ordovician were replaced by large areas of land, which led to the drying up of the climate.

In the Silurian seas, graptolites lived out their lives, trilobites fell into decline, but cephalopods reached exceptional prosperity. Corals gradually replaced the archaeocyath.

In the Silurian, peculiar arthropods developed - giant crustaceans, reaching up to 2 m in length. By the end of the Paleozoic, the entire group of crustaceans almost died out. They resembled a modern horseshoe crab.

A particularly noteworthy event of this period was the appearance and distribution of the first representatives of vertebrates - armored "fish". These “fishes” only resembled real fish in shape, but belonged to another class of vertebrates - jawless or cyclostomes. They could not swim for a long time and mostly lay at the bottom of bays and lagoons. Due to a sedentary lifestyle, they were incapable of further development. Of the modern representatives of cyclostomes, lampreys and hagfishes are known.

A characteristic feature of the Silurian period is the intensive development of terrestrial plants.

One of the first terrestrial, or rather amphibious, plants were psilophytes, leading their lineage from green algae. In reservoirs, algae adsorb water and substances dissolved in it over the entire surface of the body, which is why they do not have roots, and the outgrowths of the body, resembling roots, serve only as attachment organs. In connection with the need to conduct water from the roots to the leaves, a vascular system arises.

The emergence of plants on dry land is one of the greatest moments of Evolution. It was prepared by the previous evolution of the organic and inorganic world.

DEVONIAN. Devon - the period of fish. The climate of the Devonian was more sharply continental, icing occurred in the mountainous regions of South Africa. In warmer regions, the climate changed towards greater desiccation, desert and semi-desert areas appeared.

In the seas of the Devonian, fish reached great prosperity. Among them were cartilaginous fish, fish with a bone skeleton appeared. According to the structure of the fins, bony fish are divided into ray-finned and lobe-finned. Until recently, it was believed that the crossopterans became extinct at the end of the Paleozoic. But in 1938, a fishing trawler delivered such a fish to the East London Museum and it was named coelacanth.

At the end of the Paleozoic, the most significant stage in the development of life was the conquest of land by plants and animals. This was facilitated by the reduction of sea basins, the rise of land.

Typical spore plants emerged from psilophytes: club mosses, horsetails, ferns. The first forests appeared on the earth's surface.

By the beginning of the Carboniferous, there was a noticeable warming and humidification. In the vast valleys and tropical forests, in the conditions of continuous summer, everything grew rapidly upwards. Evolution has opened a new way - reproduction by seeds. Therefore, gymnosperms picked up the evolutionary baton, and spore plants remained a side branch of evolution and receded into the background.

The emergence of vertebrates on land occurred in the late Devonian period, after the land conquerors - psilophytes. At this time, the air was already mastered by insects, and the descendants of lobe-finned fish began to spread over the earth. The new way of transportation allowed them to move away from the water for some time. This led to the emergence of creatures with a new way of life - amphibians. Their most ancient representatives - ichthyoskhegi - were found in Greenland in Devonian sedimentary rocks.

The heyday of ancient amphibians is dated to the Carboniferous. It was during this period that stegocephals were widely developed. They lived only in the coastal part of the land and could not conquer the inland massifs located far from water bodies.