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

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

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

The names of eonotems and groups come from Greek words:

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

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

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

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

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

Tab. 1. Geological table

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

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

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

The stratigraphic scale (geochronological) is the 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 have been studied using modern methods, including uranium-lead, and as a result, age estimates are presented solar system. 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, does not have of great importance for 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). This is not surprising. 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 very distant from us left their imprints on facing granite and marble.

anthropogen

The last period of the Cenozoic era - modern stage terrestrial history, including 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. Southern Hemisphere did not recognize such huge upheavals, so the plants and animals of the Pleistocene are still present in many species. 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 on land dominated by mammals - 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.

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

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

Distinguish between relative and absolute geochronology.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Geological scale

CLARKES

Relief

geographic pole

[edit]

This term has other meanings, see Pole.

geographic pole- the point at which the Earth's axis of rotation intersects the Earth's surface. There are two geographic poles: the North Pole - located in the Arctic (the central part of the Arctic Ocean) and the South Pole - located in Antarctica.

All meridians converge at the geographic pole, and therefore the geographic pole has no longitude. The north pole has a latitude of +90 degrees and the south pole has a latitude of −90 degrees.

There are no cardinal points at the geographic poles. At the poles there is no change of day and night, since the poles do not participate in daily rotation Earth.

At the geographic pole, the angle of elevation of the Sun does not exceed 23.5 °, because of this, the temperature at the pole is very low.

The position of the geographic poles is conditional, since the instantaneous axis of rotation of the Earth moves. Because of this, there is a movement of geographic poles.

[edit] See also

magnetic pole- a conditional point on the earth's surface at which the earth's magnetic field is directed strictly at an angle of 90 ° to the surface.

[edit]

From Wikipedia, the free encyclopedia

This term has other meanings, see Relief (meanings).

Layout with terrain

Relief(fr.
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relief, from lat. relevo- I raise) - a set of uneven land, the bottom of the oceans and seas, diverse in shape, size, origin, age and history of development. It is composed of positive (convex) and negative (concave) shapes.

The relief is formed mainly as a result of a long-term simultaneous impact on the earth's surface of endogenous (internal) and exogenous (external) processes. The relief is studied by geomorphology.

The main landforms are mountains, hollows, ridges, and hollows.

On large-scale topographic and sports maps, the relief is depicted by isohypses - horizontal lines, numerical marks and additional conventional signs. On small-scale topographical and physical maps relief is indicated by color (hypsometric coloring with clear or blurred steps) and hillshade.

Denudation plains arise on the site of destroyed mountains.
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Accumulative plains are formed during the long-term accumulation of strata of loose sedimentary rocks at the site of extensive subsidence of the earth's surface.

Folded mountains - uplifts of the earth's surface that occur in mobile zones of the earth's crust, most often at the edges of lithospheric plates. Blocky mountains arise as a result of the formation of horsts, grabens and the movement of sections of the earth's crust along faults. Folded-blocky mountains appeared on the site of sections of the earth's crust that in the past underwent mountain building, transformation into a denudation plain and repeated mountain building. Volcanic mountains are formed during volcanic eruptions.

Hypsographic curve(from other Greek ὕψος - ʼʼheightʼʼ and γράφω ʼʼI writeʼʼ, also hypsometric curve) is an empirical integral distribution function of the ocean depths and the heights of the earth's surface. Usually depicted in coordinate plane, where the height of the relief is plotted along the vertical axis, and the proportion of the surface whose relief height is greater than the specified one is plotted along the horizontal axis. The part of the curve below sea level is called the bathygraphic curve.

The hypsographic curve was first constructed in 1883 by A. Lapparan and refined in 1933 by E. Kossina. Refinements for the bathygraphic curve were made in 1959 by VN Stepanov.

The hypsographic curve of the Earth's relief has two flat sections: one of them is at sea level, the other is at a depth of 4-5 km. These areas correspond to the presence of two rocks of different density. The gently sloping section at sea level corresponds to light rocks consisting of granite (density 2800 kg / m³), ​​the lower section - to heavy sells, composed of basalts (3300 kg / m³). Unlike the Earth, the hypsographic curve of the Moon does not contain flat sections, which indicates the absence of rock differentiation.

CLARKES elements, numbers expressing the average content of chemical. elements in the earth's crust, hydrosphere, the Earth as a whole, cosmic. bodies, etc.
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geochem. or cosmochem. systems. Distinguish weight (in%, in G/T or in g/ G) and atomic (in % of the number of atoms) clarks. Synthesis of data on chem. the composition of various rocks that make up the earth's crust, taking into account their distribution to depths of 16 km m was first made by Amer.
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scientists F. W. Clark(1889). The figures obtained by him for the percentage of chemical. Elements in the composition of the earth's crust, subsequently somewhat refined by A.E. Fersman, at the suggestion of the latter, were called Clark numbers, or klarkami. The average content of elements in the earth's crust, in modern.
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understanding it as the upper layer of the planet above the Mohorovichic boundary (see. Mohorovichi surface), calculated by A.P. Vinogradov(1962), amer.
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scientist S. R. Taylor (1964), German. - K. G. Vedepol (1967) (see table). Elements of small serial numbers predominate: 15 most common elements, clarks of which are above 100 g / T, have serial numbers up to 26 (Fe). Elements with even serial numbers make up 87% of the mass of the earth's crust, and with odd numbers - only 13%. Average chem. The composition of the Earth as a whole was calculated on the basis of data on the content of elements in meteorites (see Fig. Geochemistry).

Since K. elements serve as a standard for comparing low or high concentrations of chemical. elements in mineral deposits, rocks or entire regions, knowledge of them is important in prospecting and prom. assessment of mineral deposits; they also make it possible to judge the violation of the usual relations between similar elements (chlorine - bromine, niobium - tantalum) and thus point to various physicochemical. factors that disturbed these equilibrium relations.

In processes element migrations K. Elements are quantities, an indicator of their concentration.

The earth's crust contains many elements, but most of it is oxygen and silicon.

Averages chemical elements in the earth's crust are called clarks. The name was introduced by the Soviet geochemist A.E. Fersman in honor of the American geochemist Frank Wigglesworth Clark, who, after analyzing the results of the analysis of thousands of rock samples, calculated the average composition of the earth's crust. The composition of the earth's crust calculated by Clark was close to granite, a common igneous rock in the continental earth's crust.

After Clark, the Norwegian geochemist Victor Goldschmidt took up the determination of the average composition of the earth's crust. Goldschmidt made the assumption that the glacier, moving along the continental crust, scrapes off and mixes the rocks that come to the surface. For this reason, glacial deposits or moraines reflect the average composition of the earth's crust. After analyzing the composition of banded clays deposited on the bottom of the Baltic Sea during the last glaciation, the scientist obtained the composition of the earth's crust, which was very similar to the composition of the earth's crust calculated by Clark.

Subsequently, the composition of the earth's crust was studied by Soviet geochemists Alexander Vinogradov, Alexander Ronov, Alexei Yaroshevsky, and the German scientist G. Vedepol.

After analyzing all scientific works It was found that the most common element in the composition of the earth's crust is oxygen. His Clark is 47%. The next most common chemical element after oxygen is silicon with a clarke of 29.5%. Other common elements are: aluminum (clarke 8.05), iron (4.65), calcium (2.96), sodium (2.5), potassium (2.5), magnesium (1.87) and titanium (0.45). Together, these elements make up 99.48% of the total composition of the earth's crust; they form numerous chemical compounds. The clarks of the remaining 80 elements are only 0.01-0.0001, and in this regard, such elements are called rare. If the element is not only rare, but also has a weak ability to concentrate, it is called rare scattered.

In geochemistry, the term ʼʼtrace elementsʼʼ is also used, which means elements whose clarks in this system are less than 0.01. A.E. Fersman plotted the dependence of atomic clarks for even and odd elements of the periodic system. It turned out that with the complication of the structure atomic nucleus clarks are decreasing. But the lines constructed by Fersman turned out to be not monotonous, but broken. Fersman drew a hypothetical middle line: elements located above this line, he called redundant (O, Si, Ca, Fe, Ba, Pb, etc.), below - deficient (Ar, He, Ne, Sc, Co, Re, etc.). ).

You can get acquainted with the distribution of the most important chemical elements in the earth's crust using this table:

Age of the Earth- time, ĸᴏᴛᴏᴩᴏᴇ has passed since the formation of the Earth as an independent planet. According to modern scientific data, the age of the Earth is 4.54 billion years (4.54·10 9 years ± 1%). These data are based on radioisotope dating not only of terrestrial samples, but also of meteorite matter. Οʜᴎ are obtained primarily using the lead-lead method. This figure corresponds to the age of the oldest terrestrial and lunar samples.

After scientific revolution and the development of radioisotope dating methods, it turned out that many samples of minerals are over a billion years old. The oldest found so far are small zircon crystals from the Jack Hills in Western Australia - their age is at least 4404 million years. Based on a comparison of the mass and luminosity of the Sun and other stars, it was concluded that the solar system should not be much older than these crystals. Calcium- and aluminum-rich nodules found in meteorites are the oldest known specimens to have formed within the solar system: they are 4567 million years old, making it possible to establish the age of the solar system and an upper bound on the age of the Earth. There is a hypothesis that the accretion of the Earth began shortly after the formation of calcium-aluminum nodules and meteorites. Because the exact time of Earth's accretion is unknown and various models give anywhere from a few million to 100 million years, the exact age of the Earth is difficult to determine. At the same time, it is difficult to determine the absolutely exact age of the oldest rocks that come to the surface of the Earth, since they are composed of minerals of different ages.

Time in geology

The determination of the age of rocks is based on the study of the sequence of formation of strata in the earth's crust. On the basis of data on organic remains, composition, structure and location of layers relative to each other in the vertical and horizontal directions, a geochronological scale has been developed that reflects the geological history of the Earth. In accordance with the geochronological scale, a stratigraphic scale has been created, which indicates the rock complexes that were formed in geological periods of time. Below is the ratio of basic geochronological and stratigraphic units, ᴛ.ᴇ. geological time intervals and rock complexes formed in the corresponding time interval. Geological time interval: Era-Period-Epoch-Century The complex of rocks formed during this interval: Group-System-Department-Tier Thus, during an era a complex of rocks called a group was formed, during a period a complex of rocks called a system, and so on. In the geochronological scale (Table 2.1.1.3.1), there are five largest intervals of geological time - eras, each of which is divided into periods, and each period - into epochs. They make up geochronological scales with more fractional chronological intervals: epochs are divided into centuries. The divisions of the stratigraphic scale usually have the same names. For example, the Cenozoic era corresponds to the Cenozoic group of rocks, and during the Neogene period, rock complexes of the Neogene system were formed, etc. In this case, the names of the epochs often do not coincide with the names of the departments. Aeon Era Period Epoch Duration (age from the beginning of the era), million years Phanerozoic Cenozoic KZ Quaternary Q 1,8 Neogene N Pliocene N 2 Miocene N 1 (23±1) Paleogene P Oligocene P3 Eocene P2 Paleocene P1 (65±3) Mesozoic MZ Chalky K Late K 2 Early K 1 (135±5) Jurassic J Late J3 Medium J2 Early J1 55-60 (190±5) Triassic T Late T3 Medium T2 Early T1 40-45 (230±10) Paleozoic PZ Late PZ 2 Permian P Late P2 Early P1 50-60 (285±15) Coal C Late C3 Medium C2 Early C1 50-60 (350±10) Devonian D Late D3 Medium D2 Early D1 (405±10) Early PZ 1 Silurian S Late S2 Early S1 25-30 (435±15) Ordovician O Late O 3 Medium O2 Early O 1 45-50 (480±15) Cambrian Є Late Є 3 Medium Є 2 Early Є 1 90-100 (570±20) Proterozoic PR Wend (~680) (2600±100) archaeus AR (4600±200)

Determination of the relative age of rocks - this is the establishment of which rocks were formed earlier, and which - later. The relative age of sedimentary ᴦ.p. is established using geological-stratigraphic (stratigraphic, lithological, tectonic, geophysical) and biostratigraphic methods. The stratigraphic method is based on the fact that the age of a layer at normal occurrence is determined - their underlying layers are older, and the outlying ones are younger. This method should also be used for folded layers. Should not be used with overturned folds. The lithological method is based on the study and comparison of the composition of rocks in different outcrops (natural - in the slopes of rivers, lakes, seas, artificial - quarries, pits, etc.). On a territory limited in area, deposits of the same material composition (ᴛ.ᴇ. consist of the same minerals and rocks), are of the same age. When comparing sections of different outcrops, marker horizons are used, which are clearly distinguished from other rocks and are stratigraphically sustained over a large area. The tectonic method is based on the fact that powerful deformation processes ᴦ.p. appear (as a rule) simultaneously in large areas, in connection with this, strata of the same age have approximately the same degree of dislocation (displacement). In the history of the Earth, sedimentation was periodically replaced by folding and mountain building. in this case, various unconformities serve as boundaries dividing the sections into separate strata. Geophysical methods are based on the use of the physical characteristics of deposits (resistivity, natural radioactivity, residual magnetization ᴦ.p., etc.) when they are divided into layers and compared. rocks in boreholes based on resistivity measurements ᴦ.p. and porosity, it is customary to call electric logging, based on measurements of their radioactivity - gamma logging. The study of residual magnetization ᴦ.p. called the paleomagnetic method; it is based on the fact that magnetic minerals, precipitating, will spread out in accordance with the magnetic field of the Earth of that era, which, as you know, constantly changed during geological time. This orientation is maintained permanently, if the rock is not subjected to heating above 500C (the so-called Curie point) or intense deformation and recrystallization. Therefore, in different layers, the direction magnetic field will be different. Paleomagnetism allows thus. compare deposits that are significantly distant from each other (the west coast of Africa and the east coast of Latin America). Biostratigraphic or paleontological methods consist in determining the age of ᴦ.p. using the study of fossil organisms (paleontological methods will be discussed in detail in the next lecture). Determination of the relative age of magmas. And metam. G.p. (everything is higher character.
Hosted on ref.rf
Methods - for determining the age of sedimentary rocks) is complicated by the lack of paleontological remains. The age of effusive rocks occurring together with sedimentary rocks is determined by the ratio to sedimentary rocks. The relative age of intrusive rocks is determined by the ratio of igneous rocks and enclosing sedimentary rocks, the age of which is established. Determining the relative age of metamorphic rocks is similar to determining the relative age of igneous rocks.

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From Wikipedia, the free encyclopedia

Geological scale
Aeon	Era	Period
F a n e ro z o o y	Cenozoic	Quaternary
Neogene
Paleogene
Mesozoic	a piece of chalk
Yura
Triassic
Paleozoic	Permian
Carbon
Devonian
Silurus
Ordovician
Cambrian
D o c a m b e r y	P r o t e r o o s o y	Neo-Proterozoic	Ediacaran
cryogeny
Tony
Mesoproterozoic	Stenius
Ectasia
potassium
Paleoproterozoic	Statery
Orosirium
Riasius
siderius
A r x e y	neoarchean
Mesoarchean
paleoarchaean
Eoarchean
catarchean
A source

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 CAI from the Allende meteorite according to the results of modern studies of the U-Pb isotope method is 4568.5±0.5 million years. 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 should be later than this date by millions and even many tens of millions of years.

The subsequent time in the history of the Earth was divided into various 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.

Geochronological scale depicted as a spiral

[edit]History of the scale

In the second half of the XIX 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. Most often used geographical names. So, the name of the Cambrian period comes from lat. Cambria- the name of Wales, when it was part of the Roman Empire, the Devonian - the county of Devonshire in England, the Permian - from ᴦ. Perm, Jurassic - from the Jura mountains in Europe. In honor of the ancient tribes, Vendian is named (Vendi - German name Slavic people Lusatian Sorbs), Ordovician and Silurian (tribes of the Celts Ordovicians and Silurians) periods. Names associated with the composition of the rocks were used less frequently. The Carboniferous period is named because of the large number of coal seams, and the Cretaceous because of the widespread use of writing chalk.

[edit] The principle of building a scale

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 - the time of hidden life, only soft-bodied organisms existed in it, 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)	Period (system)	Epoch (department)	Beginning years ago	Main events
Phanerozoic	Cenozoic	Quaternary (Anthropogenic)	Holocene	11.7 thousand	End ice age. Rise of civilizations
Pleistocene	2.588 million	Extinction of many large mammals. Appearance modern man
Neogene	Pliocene	5.33 million
Miocene	23.0 million
Paleogene	Oligocene	33.9 ± 0.1 million	Appearance of the first great apes.
Eocene	55.8 ± 0.2 million	The appearance of the first ʼʼmodernʼʼ mammals.
Paleocene	65.5 ± 0.3 million
Mesozoic	Chalky	145.5 ± 0.4 million	The first placental mammals. Dinosaur extinction.
Jurassic	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 (ʼʼCambrian Explosionʼʼ).
Precambrian	Proterozoic	Neoproterozoic	Ediacaran	~635 million	The first multicellular animals.
cryogeny	850 million	One of the largest glaciations on Earth
Tony	1.0 billion	Beginning of the disintegration of the Rodinia supercontinent
Mesoproterozoic	Stenius	1.2 billion	Supercontinent Rodinia, superocean Mirovia
Ectasia	1.4 billion	First multicellular plants (red algae)
potassium	1.6 billion
Paleoproterozoic	Statery	1.8 billion
Orosirium	2.05 billion
Riasius	2.3 billion
siderius	2.5 billion	Oxygen catastrophe
archaeus	neoarchean	2.8 billion
Mesoarchean	3.2 billion
paleoarchaean	3.6 billion
Eoarchean	4 billion	The emergence of primitive unicellular organisms
catarchean	~4.6 billion	~4.6 billion years ago - the formation of the Earth.

[edit] 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.

Million years

Geological scale - concept and types. Classification and features of the category "Geochronological scale" 2017, 2018.

For four and a half billion years, the Earth has been revolving around the Sun. Of course, our planet has not always been the way it is now. The face of the Earth, like the face of a living being, ages with age. The composition of the oceans and atmosphere changes, mountains grow and collapse, seas arise and dry up, rivers pave their way new way and cut deep canyons in the ancient mountains. And under the influence of these global changes, life on Earth is also changing. Whatever events took place on Earth, plants, animals and microorganisms managed to adapt to new conditions. How do we know about this? History is the science of humanity. Geology and paleontology (the science of fossils) tell about the origin of the Earth and the development of life on it. People do paleontology to answer one of the fundamental questions: how did the things we see around us come about? What path did our planet go through and how did life develop on it? How did it all come to current state ? Everywhere around us we see traces of the history of the Earth. Here is a mountain range that was once the bottom of the ocean - raised as a result of tectonic processes, eaten away by water and wind, crumpled by glaciers and destroyed by earthquakes. Traces of evolution can also be found in the human body. Many internal organs (primarily the kidneys and the hormonal system) create a liquid brackish environment inside our body, reminding us that once our ancestors lived in the seas. There are two bones in the forearms and shins - a long time ago, in those days when our ancestors learned to move on land, such a structure helped to rotate the limbs. In the human embryo at the intrauterine stages of development, gills appear and then disappear. This evidence of human origins amaze both paleontologists and you and me. The "Atlas of Dinosaurs" consistently outlines all the changes that have occurred over the long history of the Earth. The book begins with a series of excellent maps based on painstaking geological research. They show how the continents have moved over the past 620 million years. Each map is then supplemented with a story about fossils, giving an idea of ​​what plants and animals lived in this era in the sea and on land. In the last, informative part, the complex ideas and principles on which modern geology and paleontology are built are presented in an understandable language. It is worth noting that the scientific study of the Earth in the modern sense of the word began only about two hundred years ago. In those years, there were many "theories" that tried to explain why the stones are so different in shape and composition. Only over time, scientists recognized that fossils are the remains of organic life, and not the creations of human hands or a joke of nature. And after the English scientist William Smith created the science of stratigraphy, it became clear that the fossilized sea shells that are sometimes found in the mountains were not brought there by the waves of the Flood, as previously thought. These finds are explained by the system of geological formations - the layers that make up the rocks all over the world. Then scientists faced another problem: how to determine the age of rocks? Obviously, the rocks located at a depth are older than the upper ones, but in almost all regions of the world only separate fragments of the complete sequence are represented. And only after the discovery of radioactivity was created a method based on measuring the decay period of isotopes. This method made it possible to determine the age of rocks to within millions of years, although Darwin and many geologists had made fairly accurate calculations decades earlier.

And finally, scientists had to solve one more problem: how did modern continents take their current places? This question was answered by the theory of continental drift. At first, it was expressed as a bold assumption, then it took shape as a hypothesis, and today, on its basis, the theory of lithospheric plate tectonics, the fundamental concept of modern geology, has been developed. Thanks to it, we know about the movement of continents, about how continental plates move and collide with each other, how oceans arise and disappear again, and we also understand that earthquakes, volcanic eruptions, "hot zones" of the earth's crust and mountain building are manifestations of one and the same process - tectonics. This theory has helped to test many pre-existing ideas about the origin and subsequent change of the atmosphere, oceans, the Earth itself and life on it.