Geochronological table of land on biology. Geological chronology

Geological chronology, or geochronologybased on clarification geological history the most well-studied regions, for example, in the central and Eastern Europe. Based on broad generalizations, comparing the geological history of various regions of the Earth, the patterns of the evolution of the organic world at the end of the last century, the international geochronological scale was developed and adopted and adopted and adopted by an international geochronological scale, reflecting the sequence of time divisions during which certain sets of deposits were formed, and the evolution of the organic world . Thus, the international geochronological scale is the natural periodization of the history of the Earth.

Among the geochronological divisions are allocated: Eon, Era, period, era, century, time. Each geochronological unit corresponds to the deposit complex allocated in accordance with the change in the organic world and called stratigraphic: eonothem, group, system, department, tier, zone. Consequently, the group is a stratigraphic unit, and the corresponding temporary geochronological unit represents the era. Therefore, there are two scales: geochronological and stratigraphic. The first is used when they talk about relative time in the history of the Earth, and the second, when they deal with deposits, as some geological events occurred in every place of the globe. Another thing is that the accumulation of precipitation was uncommon.

• The Archean and Proterozoic Eonothemes, covering almost 80% of the existence of the Earth, are distinguished in cryptosis, since the skeletal fauna and the paleontological method for their dismemberment are completely absent in the Precontal Education. Therefore, the separation of Precambrian formations is based primarily on the general and radiometric data.
• Puerozoic Eon covers only 570 million years and the dismemberment of the corresponding sediment eonothem is based on a large variety of numerous skeletal fauna. Puerozoic Eonothem is divided into three groups: Paleozoic, Mesozoic and Cenozoic, which meet the major stages of the natural geological history of the Earth, the frontiers of which are noted by rather sharp changes in the organic world.

The names of the Eonothem and Group originate from the Greek words:

• "Archaeos" is the most ancient, oldest;
• "Proteros" - primary;
• "Paleos" - ancient;
• "Mesos" - medium;
• "Kaynos" - new.

The word "cryptos" means hidden, and "plywood" is clear, transparent, as skeletal fauna appeared.
The word "Zoya" comes from Zoikos - life. Hence, " cenozoic Era"Means the era of a new life, etc.

Groups are divided into systems, whose deposits were formed during one period and are characterized only by them inherent families or birth of organisms, and if these are plants, and species and species. Systems were allocated in various regions and at different times, starting from 1822. Currently, 12 systems are allocated, the names of most of which occur from those places where they were first described. For example, the Jurassic system is from the Jurassic Mountains in Switzerland, Perm - from the Perm province in Russia, chalk - on the most characteristic breeds - white letter of chalk, etc. The quaternary system is often called anthropogenova, since it is in this age interval a person appears.

Systems are divided into two or three departments, which correspond to the early, medium, late epochs. Departments, in turn, are divided into tiers, which are characterized by the presence of certain kinds and types of fossil fauna. And finally, tiers are divided into zones that are the most fractional part of the international stratigraphic scale, which geochronological scale Corresponds time. The names of the tiers are usually given by the geographical names of the districts, where this tier has been isolated; For example, Alandansky, Bashkir, Maastricht tiers, etc. At the same time, the zone is denoted by the most characteristic type of fossil fauna. The zone covers, as a rule, only a certain part of the region and is developed on a smaller area, rather than the deposits of the tier.

All divisions of the stratigraphic scale correspond to the geological cuts in which these units were first allocated. Therefore, such cuts are reference, typical and called stratoids, which contain only a complex of organic residues, which determines the stratigraphic volume of this strata. The determination of the relative age of any layers is compared to the detected complex of organic residues in the studied layers with the complex of fossil in the stratifier of the corresponding division of the international geochronological scale, i.e. The age of deposits is determined relative to the passionithip. That is why the paleontological method, despite its inherent flaws, remains the most important method for determining geological age mountain breeds. The definition of relative age, for example, Devonian deposits, is only indicated that these deposits are younger silurian, but ancient coal. However, to establish the duration of the formation of Devonian deposits and to make a conclusion about when (in absolute summer) there was an accumulation of these sediments - it is impossible. Only the methods of absolute geochronology are able to answer this question.

Tab. 1. Geochronological table

The problem of determining the absolute age of rocks, the duration of the existence of the Earth has long been occupied by the minds of geologists, and attempts to solve it were made many times for which they were used various phenomena and processes. Early ideas about the absolute age of land were curious. Contemporary M. V. Lomonosov French Naturalist Proteler Buffon defined the age of our planet only 74,800 years. Other scientists gave various figures not exceeding 400-500 million years. It should be noted here that all these attempts were doomed to failure in advance, since they proceeded from the constancy of the speeds of processes, which, as we know, changed in the geological history of the Earth. And only in the first half of the XX century. There was a real opportunity to measure the absolute age of rock, geological processes and land as the planet.

Geologists have to deal with thickens of rocks accumulated for the long-term geological history of the planet. It is necessary to know which of the stories studied by the territory of rocks younger, and which ancient, in which sequence they were formed, to which intervals of geological history include the time of their education, and also be able to compare the thickness of rocks by age.

The doctrine of the sequence of formation and the age of rock is called geochronology. The methods of relative and methods of absolute geochronology are distinguished.

Relative geochronology

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

These methods are based on several simple principles. In 1669, Nikolo Wall formulated the principle of superposition, stacking, that in the impudent occurring each overlying layer under the underlying. We note that in definition, the applicability of the principle is underlined only under the conditions of undisturbed location.

The method of determining the sequence of the formation of the layer, based on the principle of the wall, is often called stratigraphic. Stratigraphy - section of geology engaged in the study of the sequence of education and the dismemberment of the thickness of sedimentary, volcanogenic and sedimentary and metamorphic rocks earth Corre.

The next most important principle known as principle of intersections, Formulated by James Hatton. This principle states that any body crossing the thickness of the layers, younger than these layers.

It should be noted another important principle that stars that transformation time or deformation of rocks younger than the age of formation of these breeds.

Consider the use of these principles on the example of the thickness of sedimentary rocks that are broken down by several secant magmatic bodies.

The sequence of events is as follows. Initially, the accumulation of sedimentary thickness of the lower layer (1) was initially accumulated, then the accumulation of the overlying layers (2, 3, 4, 5), each of which is under the underlying. The accumulation of sedimentary rocks in the overwhelming majority occurs in the form of horizontally lying layers, so initially climbed and formed layers (1-5). Later, these stratas were deformed (6), and they were introduced into the body of the magmatic rocks 7. Then, again horizontally, the accumulation of the overlying layer occurring on and an introduced magmatic body began. At the same time, given that the forming layer lies on the aligned horizontal surface, it is obvious that its accumulation preceded the leveling of the territory - its erosion (8). Following the erosion of the territory, the following layer has accumulated (9). The most young formation is a magmatic body 10.
We emphasize that, considering the history of the geological development of the territory, the incision of which is depicted in the figure, we used exclusively with relative times, defining only the sequence of education bodies.

Another large group of relative geochronology methods -bostratigraphic methods . These methods are based on learning fossils - Fossil residues of organisms enclosed in layers of rocks: In the midstrain layers, rocks there are different complexes of the residues of organisms, characterizing the development of flora and fauna in one or another geological era. The basis of the methods is the principle formulated by William Smith: ato-axial precipitates contain the same or close residues of fossil organisms. This principle is complemented by another important position that stles 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 changing the organic world - the law of the evolution of Ch. Darwin. Each segment of geological time is characterized by certain representatives of flora and fauna. The determination of the age of the thickness of rock is reduced to the comparison of the fossils found in them on the time of the existence of these organisms in geological history. As a rough analogy of the essence of the method, all known methods of determining age in archeology can be obtained: if only stone tools of labor were detected during the excavations, the culture refers to the stone century, the presence of bronze tools gives the basis for its attribution to the bronze age, etc.

Among the biostratigraphic methods for a long time remained the most important method of leading forms. Guidelines are called remnants of extinct organisms relevant to the following criteria:

• these organisms existed a short period of time,
• were distributed to a significant territory
• their fossils are found and easily determined.

When determining the age among the fossils found in the study layer, the most characteristic of it is selected, then they are compared with the atlas of the guidelines describing how those or other forms are characteristic of the time interval. The first of these atlases was created in the middle of the XIX century Paleontologist G. Bronnon.

To date, the main in biostratigraphy is Method for analyzing organic complexes. When applying this method, the conclusion on relative age is based on information about the entire complex of fossils, and not on finds of single leading forms, which significantly improves accuracy.

In the course of geological studies, there are tasks not only to dismember the thickness of the age and attribute them to any interval of geological history, but also comparison - correlation - remote from each other at the same time. Most simple method The identification of simply one-time thickness is to track layers on the ground from one outcrop to another. Obviously, this method is effective only in conditions of good nude. A more versatile is a biostratigraphic method for comparing the nature of organic residues in remote cuts - the simply seed layers have the same complex of fossils. This method allows the regional and global correlation of cuts.

The principal model of using fossils for correlation of remote cuts is reflected in the figure.

At the same time are layers containing the same complex of fossils

Absolute geochronology

Methods of absolute geochronology allow you to determine the age of geological objects and events in units of time. Among these methods, the methods of isotopic geochronology are the most common, based on the time of decay of radioactive isotopes enclosed in minerals (or, for example, in the remains of wood or in the petrified bones of animals).

The essence of the method is concluded in the following. The composition of some minerals includes radioactive isotopes. Since the formation of such a mineral, the process of radioactive decay of isotopes is proceeded, accompanied by the accumulation of decay products. The disintegration of radioactive isotopes proceeds spontaneously, with a constant speed, independent of external factors; The number of radioactive isotopes decreases in accordance with the exponential law. Taking into account the constancy of the decay speed, to determine the age, it suffices to establish the amount of radioactive isotope remaining in the mineral mineral and the amount of stable isotope formed during its decay. This dependence 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. The names of isotope-geochronological methods are usually formed from the names of radioactive isotopes and the final products of their collapse: uranium-lead, potassium-argon and etc. The results of determining the age of geological objects are expressed in 106 and 109 years, or in values International system Units (C): MA and GA. This abbreviation means, respectively, "million years "and" billion years "( from lat. Mega Anna - Millom, Giga Anna - billion years).

Consider determination of age Rubidium strontium isochron. As a result of the decay of the radioactive isotope 87 Rb, the neradoactive decay product is the formation of the decay product - 87 Sr, the constant decay is 1.42 * 10-11 years -1. The use of the isochronous method involves the analysis of several samples taken from the same geological object, which increases the accuracy of determining age and makes it possible to calculate the starting isotopic composition of strontium (used to determine the formation of rock).

During laboratory studies, the contents of 87 Rb and 87 SR are determined, while the content of the latter consists of the amount of strontium, initially contained in mineral (87 Sr) 0, and strontium arising during the radioactive decay process 87 RB over the period of the mineral existence:

In practice, no content of these isotopes are measured, but their relations to a stable 86SR isotope, which gives more accurate results. As a result, the equation acquires the view

The resulting equation has two unknowns: Time T and the initial ratio of strontium isotopes. To solve the problem, several samples are analyzed, the results are applied in the form of points on the schedule in the coordinates 87 SR / 86 SR - 87 RB / 86 SR. In the case of correctly selected samples, all points fall along one straight line - isochrons (therefore, have the same age). The age of the analyzed samples is calculated by the angle of inclination of isochrona, and the initial strontium ratio is determined by intersection of the isochronous axis 87 Sr / 86 Sr.

If you do not fall on the chart of the point, you can talk about the incorrect selection of samples. In order to avoid this, the following main conditions must be observed:

• samples must be selected from one geological object (i.e. be obviously simultaneous);
• in II the following rocks should not be signs of imposed transformations that could lead to the redistribution of isotopes;
• samples should have the same isotopic composition of strontium during occurrence (unacceptable use of various rocks when building one isochrona).

Without stopping at the methods of determining the age of other methods, we only note the features of some of them.

Currently, the most accurate is considered samary - Neodymium MethodAdopted as a standard with which the data of other methods compare. This is connected so that due to geochemical features, these elements are least subject to the influence of superimposed processes, often significanton distorting or negative results of age definitions. The method is based on the decay of the isotope 147 SM to form as the final product of the decay of 144 Nd.

Potassium - Argon method is based on the decay of radioactive isotope 40 K. This method has long been and is widely used to determine the age of all genetic types of rocks. It is most effective in determining the time of formation of sedimentary breeds and minerals, for example, glauconite. With regard to magmatic and especially metamorphic rocks affected by imposed changes, this method often gives "rejuvenated" dating, which is associated with the loss of rolling argon.

Radio carbon method Based on the decay of the isotope 14 C formed in the upper layers of the atmosphere as a result of exposure to cosmic radiation on atmospheric gases (nitrogen, argon, oxygen). Subsequently, 14 C, like a non-radiant carbon isotope, forms carbon dioxide CO 2, and in its composition involved in photosynthesis, turning to be in the composition of plants and, further, the food chain is transmitted to animals. In the 14th hydrosphere, 14 s is as a result of the exchange of CO 2 between the atmosphere and the oceans, then it turns out to be in the bones and carbonate shells of the aqueous inhabitants. Intensive mixing of air masses in the atmosphere and active participation Carbon in the global cycle of chemical elements leads to equalization of concentrations 14 with atmosphere, hydrosphere and biosphere. For living organisms, an equilibrium state is achieved with a specific activity of 14 ° C, 13.56 ± 0.07 decay per minute per 1 gram of carbon. If the body dies, the arrival of 14C is stopped; As a result of radioactive decay (transition to neradoactive 14 N), the specific activity of 14 s is reduced. Measuring the value of activity in the sample and comparing it with the meaning of specific activity in the lively tissue, it is easy to calculate the time of the cessation of the body's livelihoods by the formula

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Radio carbon dating allows to determine the age of samples containing carbon (bones, teeth, shells, wood, coal, etc.) by age up to 70 thousand years. This determines its use in quaternary geology and, especially in archeology.

At the end of the consideration of the methods of isotope geology it should be noted that, despite the receipt of "absolute", expressed in years, dating, we deal with model age - The obtained results inevitably contain some error and, moreover, the duration of the astronomical year during long-term geological history has changed.

Another group of absolute geochronology methods is presented seasonally climatic methods. An example of this method is varvochronology - the method of absolute geochronology, based on the calculation of the annual layers in the "tape" sediments of the spelling lakes. For the rating lakes, the so-called "belt clay" - clearly layered precipitation consisting of a large number of parallel tapes serve. Each tape is the result of a one-year sedimentation cycle in the conditions of lakes located most of the year in the frozen state. It always consists of two layers. The upper - winter - layer is represented by the clay of the dark color (due to the enrichment of the organic) formed under the ice cover; The lower - summer - is complicated with more coarse-crushed light-colored sediments (mainly thin sands or alaver-clay sediments) formed by the material brought to the lake. Each pair of such puffs corresponds to 1 year.

The study of the rhythm of rhythm clamp allows not only to determine the absolute age, but also to conduct a correlation located near each other of the cuts, comparing the power of the layer.

At a similar principle, it is based on the annual layers in the precipitation of salt lakes, where in summer, due to the increase in evaporation, there is active precipitation of salts.

The disadvantages of seasonally climatic methods should include their non-dynamice.

Periodization of geological history. Stratigress and geochronological scale

Operating the category of relative time must have a universal periodization scale of history. So, in relation to the history of mankind, we use the expressions "BC", "in the era of the Renaissance", "in the 20th century", etc., referring to any event or subject matter of material culture to a certain temporary interval. A similar approach is accepted in geology, for these purposes an international geochronological scale has been developed and an international stratigraphic scale.

The main information on the geological history of the Earth is layers of rocks, in which, as on the pages of the Stone Chronicles, they captured the changes and evolution of the organic world that happened on the planet (the last "captured" in the complexes of fossils contained in the intercourse layers). Layers of rocks occupying a certain position in the total consistency of the simplicity and allocated on the basis of the characteristics inherent in them (more often - the complex of fossil) are stratigraphic divisions. Mountain breeds, aligning stratigraphic divisions, were formed throughout a certain interval of geological time, and, therefore, reflect the evolution of the earth's crust and the organic world over this time.

- scale, showing the sequence and coinlands of stratigraphic divisions, foundation of the earth's bore and reflecting the grounds passed historical Development. The object of the stratigraphic scale are layers of rocks. The basis of the modern stratigraphic scale was designed 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 a geochronological scale.

Geochronological scale - The relative geological time scale, showing the sequence and coencence of the main stages of the geological history of the Earth and the development of life on it. The geochronological scale is the geological time.

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

Geochronological units include geochronological divisions - geological time intervals, during which rock formations are part of this stratigraphic unit.

All stratigraphic units correspond to the units of the geochronological scale.

At the same time, almost all the stratigraphic divisions of the Eonothem rank - the system have unified generally accepted international names.

The largest stratigraphic divisions are acute men and eonothem. The Archean and Proterozoic Acocoites are united under the name "Precambria" (i.e., the thickness of the breeds accumulated to the Cambrian period is the first period of Puerozoic) or "Cryptose". The skeletal organisms in the layers of the rocks of the residues of skeletal organisms in the layers of the rocks of skeletal organisms in the layers of the puffer. In the Precambrian, organic residues are rare, because soft tissues are quickly destroyed, without having time to burn. The term "cryptose" itself is formed when firing the roots of words "Cryptos" - hiddenand Zoe - Life. In dismembering the Precambrian stratification for fractional stratigraphic divisions, the methods of isotopic geochronology have a crucial role, since the organic residues are rare or absent, are determined with difficulty and, the main thing is not subject to fast evolution (the same type of microfauna complexes remain unchanged for huge time intervals, which does not allow us to displace Thick on this feature).

Eonothemes include in their composition Erates. Eratea, or group- posting formed during era; The duration of the ER in plywood is the first hundreds of millions of years. Erates reflect major stages of land development and organic world. The boundaries between Erates correspond to the turning point in the history of the development of the organic world. Three Erates are distinguished in the plyhouse: Paleozoic, Mesozoic and Cenozoic.

Erates, in turn, include in their composition of the system. System- these are deposits formed during period; The duration of periods is tens of millions of years. One system from another is characterized by complexes of fauna and flora at the level of superfamily, families and childbirth. 12 systems are allocated to the plywood: Cambrian, Ordovican, Silurian, Devonian, coal (carbon), Perm, Triadia, Jurassic, Chalk, Paleogene, Neogenic and Quaternary (anthropogen). The names of most systems occur from the geographical names of those locality where they were first set. For each system on geological maps, a certain color is adopted, which is international, and an index formed by the initial letter of the Latin System Name.

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

As part of the department, tiers are allocated. Tier- deposits formed in for century; The duration of the centuries is several million years.

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

To regional stratigraphic divisions Believe the horizon and leave.

Horizon- The main regional division of the stratigraphic scale, combining attendant deposits, characterized by a certain complex of lithological and paleontological signs. The horizons are assigned geographical names corresponding to the places where they are most well represented and studied. Geochronological equivalent serves time. For example, the Haprovsky skyline, common on the coast of the Taganrog Bay of the Azov Sea, corresponds to the thicker of river sands formed at the end neogene Period. Passionate (the most representative section of the stratigraphic horizon, which is its reference) of this horizon is located at Art. Hapra. We add that the term "horizon", used without a geographical name, is understood as a layer or pack of layers allocated on the basis of any features (paleontological or lithological), that is, is the designation of free use.

Loneit is part of the horizon of the fauna and flora highlighted on the complex, characteristic of the region, and reflects a certain phase of the development of the organic world of this region. The name of the climb is given by the type of index. The geochronological equivalent of the pub is time.

Local stratigraphic divisions Presents the thickness of rocks allocated for a number of signs, mainly in a lithological or petrographic composition.

Complex - The largest local stratigraphic division. The complex has a very greater power, the complex composition of rocks formed for some major stage in the development of the territory. The complex is assigned geographical name at the distinguished place for its development. Most often, the complexes are highlighted in the dismemberment of metamorphic thickness.

Series covers a sufficiently powerful and complex stroke of rocks for which there are some general signs: Similar formation conditions, the predominance of certain types of rocks, close degree of deformations and metamorphism, etc. Series typically correspond to a single major cycle of territory development.

The main unit is local stratigraphic divisionsit is a retinue. Sweet It is a thickness of rocks formed in a certain physico-geographical environment and occupying a prescribed stratigraphic position in the context. The main features of the suite - the presence of sustainable lithological signs on the entire area of \u200b\u200bits distribution and clear severity of boundaries. The retinue is obtained by the geographical location of the passionate.

The boundaries of local stratigraphic units often do not coincide with the boundaries of uniform stratigraphic divisions.

In the process of work, the geologist often has to be used also auxiliary stratigraphic divisions - fatty, pack, layer, deposit, etc., called usually according to characteristic breeds, color, lithological features or by characteristic organic residues (thickness of limestone, layers with Matra Fabriana, etc.).

In our schools and institutions, officially teach the idea that the age of our land is calculated by many millions of years. To confirm this point of view, both scientific, a geochronological table with long eras and periods, which scientists allegedly calculated in the layers of sedimentary rocks and their fossils in them. Give an example of a lesson:

"Teacher: For many years geologists, studying rock rocks, tried to determine the age of the earth. But even recently they were far from success. In early 17th century, Archbishop Arma - James Asher, calculated the date of creation of the world in the Bible, and determined it as 4004. n. e.

But he became mistaken more than a million times. Today, scientists believe that the age of the earth is 4,600 million years. Science, which is engaged in the study of the age of land in the location of rocks, is called geology. "

(Geochronological table photo №1)

(Geochronological table photo №2)

These these students take on faith, trusting the word to the teacher and without checking, and how true this information and whether it corresponds to reality. In fact, many scientific evidence has been known for a long time, which geochronological table is shown invalid. There are scientists who have another point of view for periods of history of our Earth. For example, the geological model of Walker, modified by Cleverberg:

(Geochronological table photo №3)

I think every person, a student, he or a teacher, must thoroughly tweak those official data that he receives and form his own beliefs, based not on biased guesses, but on scientific research. To figure out which hypotheses of scientists closer to the truth, and which are not, read articles on the other point of view on a geochronological table than the official point of view, taught in educational institutions.

Geochronology- Sequence of geological events in time, their duration and coinlaughter:

- relative geochronology reflects the natural stages in the history of the development of the Earth, based on the principle of the sequence of the presentation and uses the method of biostratigraphic constructions;

- Absolute geochronology determines the age and duration of the geochronological scales units in the intervals of the modern astronomical year (in astronomical units). It is based on the study of radioactive decay products in minerals.

Geochronological(Geoistoric) scale is a hierarchical system of geochronological units equivalent to units of a common stratigraphic scale.

Stratigraphic division (Unit) - a set of rocks that make up a certain unity on a set of signs (the peculiarities of the real composition, organic residues), which allows it to be separated in the context and trace the area.

The patterns of development and formation of the earth's crust examines historical geology. The age of rock is absolute and relative.

Absolute age - The duration of the existence (life) of rock, expressed in years. It uses methods based on the use of radioactive transformations, which take place in some chemical elements (uranium, potassium, rubidium), which are part of the breeds. The age of the magmatic rocks, as well as the chemical precipitation is equal to the age of the components of their minerals. Other breeds are younger than minerals.

The ratio of the amounts of jointly located radioactive source isotope and the sustainable element formed from it gives an idea of \u200b\u200bthe age of accommodating their breeds. Methods for determining absolute age got their name from radioactive decay products: urano-lead (lead), helium, potassium-argon (argon), potassium-calcium, rubidium-strontium et al. So, knowing how much lead is formed from 1 g of uranium per year, defining their joint content in this mineral, you can find the absolute age of the mineral and the rock in which it is located. According to carbon 14 s, the half-life of which is 5568 years old, it is possible to establish agents that appeared later. It is possible to establish the absolute age of rocks by the geochronological scale of the earth's crust (Table). The determination of the absolute age of rocks is a very difficult task, the solution of which was only possible in the 50th years of the XX century.

Geochronological scale of earthly crust

The younger than the age-defined age of mineral, the more it is required for analysis, since the decay products do not have accumulated.

Stages of the development of the planet. Of great importance for geographic science has 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 their history. The history of the development of the planet Earth is divided into two stages: planetary and geological.

Planetary stage It covers a period of time from the origin of the Earth as the planet and before the formation of the earth's crust. The scientific hypothesis on the formation of land (as a space body) appeared on the basis of general views on the emergence of other planets, which are part of Solar system. The fact that the Earth is one of the 8 planets of the solar system, you know from the course of grade 6. Planet Earth formed 3.5-5 billion years ago. This stage ended with the advent of primary lithosphere, atmospheric and hydrosphere (3.7-3.8 billion years ago).

Geological stage Began since the appearance of the first primaries of the earth's crust, which continues to the present. During this period, various rocks were formed. The earth's crust has repeatedly been slow raised and lowering under the influence of the internal forces. During the periods of lowering the territory, sedimentary breeds (sands, clays, etc.) were postponed at the bottom, and during the periods of the bottom of the sea, plains were arisen with these sedimentary rocks.

Thus, the initial structure of the earth's crust began to change. This process continued continuously. At the bottom of the seas and depression of the mainland, a sedimentary layer of rocks was accumulated, among which there were remnants of plants and animals. Each geological period corresponds to their certain forks, because the organic world is in constant development.

Determination of the age of rocks. In order to determine the age of the Earth and present the history of its geological development, use the methods of relative and absolute chores (geochronology).

To determine relative age of rocks,it is necessary to know the patterns of consistent occurrence of layers of sedimentary rocks. of different composition. Their essence is as follows: if the elephant sedimentary rocks lie in an impudent state, as they put on the other at the bottom of the Maore, then it means that the layer underlying downwards was postponed earlier, and the layer underlying above was formed later, Consequently, he is younger.

Indeed, if there is no lower layer, it is clear that the covering the upper layer cannot form, therefore the lower the sedimentary layer is located, the greater its age. The topmost layer is considered the youngest.

In determining the relative age of rock great importance It has the study of the sequential occurrence of sedimentary rocks of different compositions and the petrified remnants of animals and vegetable organisms contained in them. As a result of the painstaking work of scientists, but the determination of the geological age of rocks and the development of plant and animal organisms was compiled a geochronological table. It was approved at the II International Geological Congress in 1881 in Bologna. It is based on the stages of the development of life identified by paleontology. This table scale is constantly being improved. The current state of the table is given on with. 45.

Units of the scale are era. They are divided into periods that are divided into epochs. The five largest of these units (era) are names associated with the nature of life that existed then. For example, aRHEY - time early Life, p [Yeterozoa - the era of primary life, paleozoic - Era of an ancient life, mesoza - Era of Middle Life, cenozoa - Era of a new life.

The eras are divided into less long time segments - periods (sometimes they are called systems). The names are different. Some of them come from the names of rocks that are most characteristic for this time (for example carboan period in Paleozoa I. cretaceous period in mesozoic). Most periods are named but the localities in which the deposits are most fully represented by one or another period and where for the first time these deposits were characterized. The oldest Paleozoic period - keb Rysky Got a name from Cambria - ancient state in the west of England. Names of the following periodsleose - ordovikand silurian- It comes from the names of the ancient tribes of Ordovikov and the Silurists who inhabited the territory of the current Wales.

To distinguish the geochronological table systems, conventional signs are taken. Geological era are denoted by indices (signs) - the initial letters of their Latin names (for example, Archey -AR) and the indices of periods - the first letter of their Latin names (for example, Perm R).

Definition absolute age rock It began at the beginning of the 20th century, after the law of decay of radioactive elements was opened. Its essence is as follows. In the depths of the Earth there are radioactive elements, such as uranium. Over time, it is slowly, with a constant speed, disintegrates on helium and lead. Helium is dissipated, and lead remains in the breed. Knowing the sprouting rate of uranium (from 100 g of uranium, 1 g of lead is distinguished for 74 million), according to the number of lead contained in rocks, you can calculate how many years ago it was formed.

The use of radiometric methods made it possible to determine the age of many rocks, gorgeous crop. Thanks to these studies, it was possible to establish the geological and planetary age of the Earth. On the basis of the relative and absolute methods of churches, a geochronological table was composed.

1. What stages are the geological history of land development?

2. What stage of land development is geological?

3 *. How do the relative and absolute age of rock determine?

1. Compare PO geochronological table The duration of geological er and periods.