| Akron (acrotheme) | Aeon (eonoteme) | Era (erathema) | Period (system) | Epoch (Department) | completion, years ago | Tectonic cycles | Main developments |
|---|---|---|---|---|---|---|---|
| fz Phanerozoic | kz Cenozoic | Quaternary | Holocene | Continues these days | Alpine cycle There are only 2 belts on Earth. The Tethys Ocean disappears. From the end of the Neogene, the glaciation begins in Antarctica. Tt.o. Neogene - the largest geocratic period of the Earth. The area of the continents was larger than modern. All shelf zones were part of the continents. | Extinction of many large mammals. | |
| Pleistocene | 11 400 | The emergence of modern man. | |||||
| Neogene | Pliocene | 1.81 million | |||||
| Miocene | 5.33 million | ||||||
| Paleogene | Oligocene | 23.0 million | Appearance of the first great apes. | ||||
| Eocene | 37.2 million | The emergence of the first "modern" mammals. | |||||
| Paleocene | 55.8 million | ||||||
| mz Mesozoic | Chalky | 66.5 million | Pacific cycle On Earth there is 1 continent, 2 oceans and 3 belts. The dominance of land on Earth, the climate is hot dry. The split of Gondwana completely. | The first placental mammals. Dinosaur extinction. | |||
| Jurassic | 146 million | The appearance of marsupials and the first birds. The rise of the dinosaurs. | |||||
| Triassic | 200 million | The first dinosaurs and egg-laying mammals. | |||||
| pz Paleozoic | Permian | 251 million | Herzing cycle In the Carboniferous, a new supercontinent, Angarida, at that time Eria and Gondwana already existed. Eria + Angarida = Laurasia Laurasia + Gondwana = Pangea But immediately a split begins (at the end of Perm). At the end of Perm, the first great extinction of organisms. | About 95% of all existing species died out. | |||
| Coal | 299 million | The appearance of trees and reptiles. | |||||
| Devonian | 359 million | The appearance of amphibians and spore plants. | |||||
| S Silurian | 416 million | Caledonian cycle At this stage, there were 6 ancient platforms on Earth. The largest transgression with max in the Ordovician, Gondwana remains dry land. At the beginning of the Silurian - glaciation. At the end of the Caledonian phase, the supercontinent Eria formed. | Exit of life to land: scorpions and later the first plants. The appearance of fish. | ||||
| O Ordovician | 443 million | The pelagial is inhabited by cephalopods | |||||
| E Cambrian | 488 million | Appearance a large number new groups of organisms. | |||||
| PR Proterozoic | Riphean (Neoproterozoic) | Ediacarus (obsolete Vendian) | 542 million | Baikal cycle 5 geosynclinal belts are laid. Formed Pacific Ocean(800 million years ago) At the end of the Riphean, all continents are connected southern hemisphere- Gondwana. The climate is warm everywhere, at the end of the Riphean glaciation. The atmosphere is saturated with oxygen (1% of the current level) | The first multicellular animals. | ||
| cryogeny | 600 million | ||||||
| Tony | 850 million | ||||||
| Late (Mesoproterozoic) | Stenius | 1.0 billion | |||||
| Ectasia | 1.2 billion | ||||||
| potassium | 1.4 billion | ||||||
| Early (Paleoproterozoic) | Statery | 1.6 billion | Karelian cycle Revolutionary stage. At the end of it, huge sections of the ZK become rigid and stable. Real platforms are being formed. | ||||
| Orosirium | 1.8 billion | ||||||
| Riasius | 2.05 billion | ||||||
| siderius | 2.3 billion | ||||||
| AR archaeus | Late | neoarchean | 2.5 billion | White Sea cycle Formation of a real continental ZK. | |||
| Mesoarchean | 2.8 billion | ||||||
| Early | paleoarchaean | 3.2 billion | Soami cycle On Earth, a hydrosphere is formed, which is represented by shallow oceans, in the form of islands there are cores of the protocontinental crust. | ||||
| Eoarchean | 3.6 billion | The emergence of primitive unicellular organisms. | |||||
| 3.8 billion | Early geological stage The Earth is formed as a result of rotation. Substance differentiation begins. A basaltic crust is formed, but it is phantom. | Formation of the Earth 4.57 billion years ago | |||||
Geological table
This is a list of time divisions or intervals, in the order of their hierarchy.
Chronometric scale
This is an isotopic age scale based on the radioactive decay of elements, from their formation to the present day.
Akron is a time period lasting 2 billion years.
Eon - a gap of 1 billion years.
An era is hundreds of millions of years.
Period - tens of million years
Epoch - tens of millions of years.
Stratigraphic scale
This is the rock scale. Represents a complete perfect section of the Earth's crust
See also: Evolution of the geographic shell of the earth, Geochronological scale (original article).
The history of the planet Earth already has about 7 billion years. During this time, our common home has undergone significant changes, which was the result of changing periods. in chronological order reveal the entire history of the planet from its very appearance to the present day.
Geological chronology
The history of the Earth, presented in the form of eons, groups, periods and epochs, is a certain grouped chronology. At the first international congresses of geology, a special chronological scale was developed, which represented the periodization of the Earth. Subsequently, this scale was replenished with new information and changed, as a result, now it reflects all geological periods in chronological order.
The largest subdivisions in this scale are eonotemes, eras and periods.
Formation of the Earth
The geological periods of the Earth in chronological order begin their history precisely with the formation of the planet. Scientists have come to the conclusion that the Earth was formed about 4.5 billion years ago. The very process of its formation was very long and, possibly, began as early as 7 billion years ago from small cosmic particles. Over time, the gravitational force grew, along with it, the speed of bodies falling on the forming planet increased. Kinetic energy was transformed into heat, resulting in a gradual heating of the Earth.
The core of the Earth, according to scientists, was formed over several hundred million years, after which the gradual cooling of the planet began. Currently, the molten core contains 30% of the mass of the Earth. The development of other shells of the planet, according to scientists, has not yet been completed.
Precambrian eon
In the geochronology of the Earth, the first eon is called the Precambrian. It covers the time 4.5 billion - 600 million years ago. That is, the lion's share of the history of the planet is covered by the first. However, this eon is divided into three more - Katarchean, Archean, Proterozoic. And often the first of them stands out in an independent eon.
At this time, the formation of land and water occurred. All this happened during active volcanic activity for almost the entire eon. Shields of all continents were formed in the Precambrian, but traces of life are very rare.
Catharhean eon
The beginning of the history of the Earth - half a billion years of its existence in science is called katarchey. The upper limit of this eon is at around 4 billion years ago.
Popular literature portrays the Catarchean as a time of active volcanic and geothermal changes on the Earth's surface. However, this is not actually true.
The Katharhean eon is a time when volcanic activity was not manifested, and the surface of the Earth was a cold, inhospitable desert. Although quite often there were earthquakes that smoothed the landscape. The surface looked like a dark gray primary substance covered with a layer of regolith. The day at that time was only 6 hours.
archean eon
The second main eon out of four in the history of the Earth lasted about 1.5 billion years - 4-2.5 billion years ago. Then the Earth did not yet have an atmosphere, and therefore there was no life yet, but in this eon bacteria appear, due to the lack of oxygen they were anaerobic. As a result of their activities, today we have deposits of natural resources such as iron, graphite, sulfur and nickel. The history of the term "archaea" dates back to 1872, when it was proposed by the famous American scientist J. Dan. The Archean eon, unlike the previous one, is characterized by high volcanic activity and erosion.
Proterozoic eon
If we consider the geological periods in chronological order, the next billion years took the Proterozoic. This period is also characterized by high volcanic activity and sedimentation, and erosion continues over vast areas.
The formation of the so-called. mountains Currently they are small hills on the plains. The rocks of this eon are very rich in mica, non-ferrous metal ores and iron.
It should be noted that the first living creatures appeared in the Proterozoic period - the simplest microorganisms, algae and fungi. And by the end of the eon, worms, marine invertebrates, and mollusks appear.
Phanerozoic eon
All geological periods in chronological order can be divided into two types - explicit and hidden. Phanerozoic refers to explicit. At this time, a large number of living organisms with mineral skeletons appear. The era preceding the Phanerozoic was called hidden because its traces were practically not found due to the absence of mineral skeletons.
The last about 600 million years of the history of our planet are called the Phanerozoic eon. The most significant events of this eon are the Cambrian explosion, which occurred approximately 540 million years ago, and the five largest extinctions in the history of the planet.
Eras of the Precambrian eon
During the Katarchean and Archean, there were no generally recognized eras and periods, so we will skip their consideration.
The Proterozoic consists of three major eras:
Paleoproterozoic- i.e. ancient, including siderium, riasian period, orosirium and staterium. By the end of this era, the concentration of oxygen in the atmosphere reached its present level.
Mesoproterozoic- average. It consists of three periods - potassium, ectasia and stenia. In this era, algae and bacteria reached their greatest prosperity.
Neoproterozoic- new, consisting of tonium, cryogenium and ediacarium. At this time, the formation of the first supercontinent, Rodinia, takes place, but then the plates parted again. The coldest ice age took place during an era called the Mesoproterozoic, during which most of the planet froze over.
Eras of the Phanerozoic eon
This eon consists of three large epochs, which differ sharply from each other:
Paleozoic, or an era of ancient life. It began about 600 million years ago and ended 230 million years ago. The Paleozoic consists of 7 periods:
- Cambrian (a temperate climate is formed on Earth, the landscape is low-lying, during this period all modern types of animals originate).
- Ordovician (the climate on the entire planet is quite warm, even in Antarctica, while the land sinks significantly. The first fish appear).
- Silurian period (the formation of large inland seas takes place, while the lowlands become increasingly arid due to land uplift. The development of fish continues. The Silurian period is marked by the appearance of the first insects).
- Devon (appearance of the first amphibians and forests).
- Lower Carboniferous (dominance of ferns, distribution of sharks).
- Upper and Middle Carboniferous (appearance of the first reptiles).
- Perm (most of the ancient animals are dying out).
mesozoic, or the time of the reptiles. Geological history consists of three periods:
- Triassic (seed ferns die out, gymnosperms dominate, the first dinosaurs and mammals appear).
- Jura (part of Europe and the western part of America is covered with shallow seas, the appearance of the first toothed birds).
- Chalk (appearance of maple and oak forests, the highest development and extinction of dinosaurs and toothed birds).
cenozoic, or the time of mammals. Consists of two periods:
- Tertiary. At the beginning of the period, predators and ungulates reach their dawn, the climate is warm. There is a maximum spread of forests, the oldest mammals are dying out. Approximately 25 million years ago, a person appears and in the Pliocene era, a person arises.
- Quaternary. Pleistocene - large mammals die out, originate human society 4 ice ages occur, many plant species die out. The modern era - the last ice age ends, gradually the climate takes on its present form. The supremacy of man on the whole planet.
The geological history of our planet has a long and contradictory development. In this process, there were several extinctions of living organisms, ice ages were repeated, periods of high volcanic activity, there were eras of the supremacy of different organisms: from bacteria to humans. The history of the Earth began about 7 billion years ago, it was formed about 4.5 billion years ago, and less than a million years ago, man ceased to have competitors in all living nature.
Students, graduate students, young scientists who use the knowledge base in their studies and work will be very grateful to you.
Hosted at http://www.allbest.ru/
abstract
Geological table of the Earth
Completed by: Mikhail Konyshev
Introduction
Geological scale- the geological time scale of the history of the Earth, used in geology and paleontology, a kind of calendar for time intervals of hundreds of thousands and millions of years.
According to modern generally accepted ideas, the age of the Earth is estimated at 4.5-4.6 billion years. No rocks or minerals have been found on the surface of the Earth that could be witnesses to the formation of the planet. The maximum age of the Earth is limited by the age of the earliest solid formations in the solar system - refractory inclusions rich in calcium and aluminum (CAI) from carbonaceous chondrites. Age of the CAI from the Allende meteorite according to the results contemporary research U-Pb isotopic 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 may be later than this date by millions and even many tens of millions of years.
Subsequent time in the history of the Earth has been divided into different time intervals according to major events which were then taking place.
The boundary between the Phanerozoic eras runs along the largest evolutionary events - global extinctions. The Paleozoic is separated from the Mesozoic by the largest Permian-Triassic extinction of species in the history of the Earth. The Mesozoic was separated from the Cenozoic by the Cretaceous-Paleogene extinction.
The history of the scale
In the second half of the 19th century, at the II-VIII sessions of the International Geological Congress (IGC) in 1881-1900. the hierarchy and nomenclature of most modern geochronological units were adopted. Subsequently, the International geochronological (stratigraphic) scale was constantly refined.
The specific names of the periods were given according to various criteria. 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, Devonian - from the county of Devonshire in England, Permian - from the city of Perm, Jurassic - from the Yuram Mountains in Europe. In honor of the ancient tribes, the Vendian (Vmends - the German name for the Slavic people of the Lusatian Sorbs), Ordovician and Silurian (tribes of the Celts Ordomviks and Silumrs) periods are named. Names associated with the composition of the rocks were used less frequently. The Carboniferous period is named because of the large number of coal seams, and the Cretaceous because of the widespread use of writing chalk.
The principle of constructing the scale
geochronological scale earth geology
The geochronological scale was created to determine the relative geological age of rocks. Absolute age, measured in years, is of secondary importance to geologists.
The time of the existence of the Earth is divided into two main intervals (eons): Phanerozoic and Precambrian (Cryptose) according to the appearance of fossil remains in sedimentary rocks. Cryptozoic is a time of hidden life, in which only soft-bodied organisms existed, leaving no traces in sedimentary rocks. The Phanerozoic began with the appearance of many species of mollusks and other organisms on the border of the Ediacaran (Vendian) and Cambrian, allowing paleontology to dissect the strata according to the finds of fossil flora and fauna.
Another major division of the geochronological scale has its origin in the very first attempts to divide the history of the earth into major time intervals. Then the whole history was divided into four periods: the primary, which is equivalent to the Precambrian, the secondary - the Paleozoic and Mesozoic, the tertiary - the entire Cenozoic without the last Quaternary period. The Quaternary period occupies a special position. This is the shortest period, but many events took place in it, the traces of which are better preserved than others.
|
Eon (eonoteme) |
Era (erathema) |
(system) |
years ago |
Main events |
|
|
Phanerozoic |
Cenozoic |
Quaternary (Anthropogenic) |
End of the Ice Age. Rise of civilizations |
||
|
Pleistocene |
Extinction of many large mammals. The emergence of modern man |
||||
|
Neogene |
|||||
|
Paleogene |
Oligocene |
33.9 ± 0.1 million |
Appearance of the first great apes. |
||
|
55.8 ± 0.2 million |
The emergence of the first "modern" mammals. |
||||
|
Paleocene |
65.5 ± 0.3 million |
||||
|
145.5 ± 0.4 million |
The first placental mammals. Dinosaur extinction. |
||||
|
199.6 ± 0.6 million |
The appearance of marsupial mammals and the first birds. Rise of the dinosaurs. |
||||
|
Triassic |
251.0 ± 0.4 million |
The first dinosaurs and egg-laying mammals. |
|||
|
Paleozoic |
Permian |
299.0 ± 0.8 million |
About 95% of all existing species died out (Mass Permian extinction). |
||
|
Coal |
359.2 ± 2.8 million |
The appearance of trees and reptiles. |
|||
|
Devonian |
416.0 ± 2.5 million |
The appearance of amphibians and spore plants. |
|||
|
Silurian |
443.7 ± 1.5 million |
Exit of life to land: scorpions; emergence of jawed |
|||
|
Ordovician |
488.3 ± 1.7 million |
Racoscorpions, the first vascular plants. |
|||
|
Cambrian |
542.0 ± 1.0 million |
The emergence of a large number of new groups of organisms ("Cambrian explosion"). |
|||
|
Precambrian |
|||||
|
Proterozoic |
Neoproterozoic |
Ediacaran |
The first multicellular animals. |
||
|
cryogeny |
One of the largest glaciations on Earth |
||||
|
Beginning of the disintegration of the supercontinent Rodinia |
|||||
|
Mesoproterozoic |
Supercontinent Rodinia, superocean Mirovia |
||||
|
First multicellular plants (red algae) |
|||||
|
Paleoproterozoic |
Statery |
||||
|
Orosirium |
|||||
|
Oxygen catastrophe |
|||||
|
neoarchean |
|||||
|
Mesoarchean |
|||||
|
paleoarchaean |
|||||
|
The emergence of primitive unicellular organisms |
|||||
|
catarchean |
~4.6 billion years ago - the formation of the Earth. |
Scale charts of the geochronological scale
Three chronograms are presented, reflecting different stages of the history of the earth on a different scale.
1. The top diagram covers the entire history of the earth;
2. The second - Phanerozoic, the time of the mass appearance of various forms of life;
3. Lower - Cenozoic, the period of time after the extinction of the dinosaurs.
Hosted on Allbest.ru
Age of rocks and methods for their determination
The concept of geological time. Degeological and geological stages of the Earth's development. Age of sedimentary rocks. Periodization of the history of the Earth. General geochronological and stratigraphic scales. Methods for determining the isotopic age of rocks.
abstract, added 06/16/2013
Physical and geological processes
The internal structure of the Earth. The concept of the mantle as the geosphere of the Earth, which surrounds the core. Chemical composition Earth. The layer of low viscosity in the upper mantle of the Earth (asthenosphere), its role and significance. Earth's magnetic field. Features of the atmosphere and hydrosphere.
presentation, added 11/21/2016
The main characteristics of the planet
Modern ideas about internal structure Earth. Radius of a heliocentric orbit. Experimental data on the structure of the globe. Earth's crust and geological chronology. Features of the geochronological scale. Processes that form the earth's crust.
abstract, added 11/11/2009
Evolutionary changes in the Earth's atmosphere
Features of the composition and structure of the Earth's atmosphere. Evolution earth's atmosphere, the process of its formation over the centuries. The appearance of the aquatic environment as the beginning of the geological history of the Earth. The content and origin of impurities in the atmosphere, their chemical composition.
abstract, added 11/19/2009
Paleomagnetic scale of reversals of the Earth's main magnetic field and the age of the ocean floor
Magnetization of linear sections oceanic crust during reversals of the main magnetic field, expansion and buildup of oceanic plates in rift zones. Drawing up a geochronological scale of paleomagnetic anomalies in the process of marine magnetic surveys.
abstract, added 08/07/2011
Characteristics of the main shells of the Earth
The main shells of the Earth: atmosphere, hydrosphere, biosphere, lithosphere, pyrosphere and centrosphere. The composition of the Earth and its physical structure. Geothermal regime of the Earth and its specificity. Exogenous and endogenous processes and their influence on the solid surface of the planet.
abstract, added 02/08/2011
Methods of historical geology and the structure of the earth's crust
The concept and tasks of historical geology. Paleontological and non-paleontological methods for reconstructing the geological past. Determination of the relative age of igneous rocks. Periodization of the history of the Earth. The concept of stratigraphic units.
abstract, added 05/24/2010
Modern mineralogical models of the Earth's mantle
Model of the structure of the Earth. The work of the Australian seismologist K.E. Bullen. The composition of the upper mantle and the mantle below the boundary of 670 km. The modern structure of the Earth. Examples of the distribution of velocity anomalies in the mantle according to seismic tomography data at different depths.
presentation, added 04/20/2017
The internal structure of the Earth
The formation of the Earth according to modern cosmological concepts. Structure model, basic properties and their parameters characterizing all parts of the Earth. The structure and thickness of the continental, oceanic, subcontinental and suboceanic crust.
abstract, added 04/22/2010
The internal structure of the Earth
The creation of a model of the internal structure of the Earth as one of the greatest achievements of science in the 20th century. Chemical composition and structure of the earth's crust. Characteristics of the composition of the mantle. Modern ideas about the internal structure of the Earth. Composition of the Earth's core.
abstract, added 03/17/2010
GEOLOGICAL CHRONOLOGY
A very important characteristic of rocks is their age. As shown above, many properties of rocks, including engineering-geological ones, depend on it. In addition, on the basis of studying, first of all, the age of rocks, historical geology recreates the patterns of development and formation of the earth's crust. An important section of historical geology is geochronology - the science of the sequence of geological events in time, their duration and subordination, which it establishes by determining the age of rocks based on the use of various methods and geological disciplines. The relative and absolute age of rocks is distinguished.
In assessing relative age, older and younger rocks are distinguished by highlighting the time of an event in the history of the Earth in relation to the time of another geological event. Relative age is easier to determine for sedimentary rocks in their undisturbed (close to horizontal occurrence) occurrence, as well as for volcanic and less often metamorphic rocks interbedded with them.
The stratigraphic (stratum - layer) method is based on the study of the sequence of occurrence and the relationship of layers of sedimentary deposits, based on the principle of superposition: each overlying layer is younger than the lower one.
It is used for strata with undisturbed horizontal occurrence of layers (Fig. 22). This method should be carefully applied when the layers are folded; first, their tops and bottoms must be determined. Young is the layer 3 , and the layers 1 and 2 - more ancient.
Lithologo — petrographic method is based on the study of the composition and structure of rocks in adjacent sections of wells and the identification of rocks of the same age - correlation of sections . Sedimentary, volcanic and metamorphic rocks of the same facies and age, such as clays or limestones, basalts or marbles, will have similar textural and structural features and composition.
Geological time scale for the history of life on Earth
Older rocks tend to be more altered and compacted, while younger ones are slightly altered and porous. It is more difficult to use this method for thin continental deposits, the lithological composition of which is rapidly changing along the strike.
The most important method for determining relative age is paleontological ( biostratigraphic ) method , based on the allocation of layers containing various complexes of fossil remains of extinct organisms. The method is based on the principle of evolution : life on Earth develops from simple to complex and does not repeat itself in its development. The science that establishes the pattern of development of life on Earth by studying the remains of fossil animals and plant organisms - fossils ( fossils) contained in the strata of sedimentary rocks is called paleontology. The time of formation of one or another rock corresponds to the time of death of organisms, the remains of which were buried under layers above the accumulated sediments. The paleontological method makes it possible to determine the age of sedimentary rocks in relation to each other, regardless of the nature of the occurrence of layers, and to compare the age of rocks occurring in distant parts of the earth's crust. Each segment of geological time corresponds to a certain composition of life forms or guiding organisms (Fig. 23-29). Leading fossils ( forms ) lived for a short period of geological time on vast areas, as a rule, in reservoirs, seas and oceans. Starting from the second half of the twentieth century. actively began to apply the micropaleontological method, including spore — pollen, to study organisms invisible to the eye. On the basis of the paleontological method, schemes of the evolutionary development of the organic world were drawn up.
Thus, based on the above methods for determining the relative age of rocks to late XIX in. a geochronological table was compiled, which includes subdivisions of two scales: stratigraphic and corresponding geochronological.
Stratigraphic subdivision (unit) - a set of rocks that make up a certain unity in terms of a set of features (features of the material composition, organic remains, etc.), which allows you to distinguish it in the section and trace about the area. Each stratigraphic unit reflects the peculiarity of the natural geological stage of the development of the Earth (or a separate area), expresses a certain geological age and is comparable to a geochronological unit.
Geochronological (geohistorical) scale - a hierarchical system of geochronological (temporal) divisions, equivalent to units of the general stratigraphic scale. Their ratio and subdivision is shown in Table. fifteen.
 |
isolated in the UK, Perm - in Russia, etc. (Table 16).
 |
 |
Absolute age - the duration of the existence (life) of the breed, expressed in years - in time intervals equal to the modern astronomical year (in astronomical units). It is based on measuring the content of radioactive isotopes in minerals: 238U, 232Th, 40K, 87Rb, 14C, etc., their decay products and knowledge of the experimentally revealed decay rate. The latter has a half-life – the time it takes for half of the atoms of a given unstable isotope to decay. The half-life varies greatly for different isotopes (Table 17) and determines the possibilities of its application.
Methods for determining the absolute age got their name from the products of radioactive decay, namely: lead (uranium-lead), argon (potassium-argon), strontium (rubidium-strontium), etc. The most commonly used potassium-argon method, since the 40K isotope contained in many minerals (mica, amphiboles, feldspars, clay minerals), decomposes with the formation of 40Ar and has a half-life of 1.25 billion years. Calculations made using this method are often verified by the strontium method. In these minerals, potassium is isomorphically replaced by 87Rb, which, upon decay, transforms into the 87Sr isotope. With the help of 14C, the age of the youngest Quaternary breeds is determined. Knowing how much lead is formed from 1 g of uranium per year, determining their combined content in a given mineral, one can find the absolute age of the mineral and the rock in which it is located.
The use of these methods is complicated by the fact that rocks during their "life" experience various events: magmatism, metamorphism, and weathering, during which the minerals "open", change and lose the isotopes and decay products partially contained in them.
Therefore, the term "absolute" age used is convenient to use, but is not absolutely accurate for the age of rocks. It is more correct to use the term "isotopic" age. A systematic correlation is made between the subdivisions of the relative geochronological table and the absolute age of the rocks, which is still being refined and given in the tables.
Geologists, builders and other professionals can obtain information about the age of rocks by studying geological maps or related geological reports. On the maps, the age of rocks is shown by the letter and color that are accepted for the corresponding subdivision of the geochronological table. Comparing the relative age of specific rocks shown by letter and color with the absolute age of the unified geochronological table, we can assume the absolute age of the studied rocks. Civil engineers must have an understanding of the age of rocks and its designation, and also use them when reading geological documentation (maps and sections) compiled when designing buildings and structures.
 |
Of particular interest is the Quaternary period (Table 18). Deposits of the Quaternary system cover the entire earth's surface with a continuous cover, their thicknesses contain remains ancient man and his household items. In these sequences, various deposits (facies) alternate and replace each other in area: eluvial, alluvial , moraine and fluvioglacial, lacustrine — marsh. Deposits of alluvial gold and other valuable metals are confined to alluvium. Many breeds of the Quaternary system are raw materials for the production of building materials. A large place is occupied by deposits of the cultural layer , resulting from human activity. They are distinguished by considerable friability and great heterogeneity. Its presence can complicate the construction of buildings and structures.
Geological table- this is one of the ways to represent the stages of development of the planet Earth, in particular life on it. The table records eras, which are subdivided into periods, their age, duration are indicated, the main aromorphoses of flora and fauna are described.
Often in geochronological tables, earlier, i.e. older, eras are written at the bottom, and later, i.e., younger ones, at the top. Below are data on the development of life on Earth in natural chronological order: from oldest to newest. Tabular form omitted for convenience.
Archean era
It began about 3500 million (3.5 billion) years ago.
Lasted about 1000 million years (1 billion).
AT archean era the first signs of life on Earth appear - single-celled organisms.
According to modern estimates, the age of the Earth is more than 4 billion years. Before the Archean, there was the Catharchean era, when there was no life yet.
Proterozoic era
It began about 2700 million (2.7 billion) years ago. It lasted more than 2 billion years.
Proterozoic - the era of early life. In the layers belonging to this era, rare and few organic remains are found. However, they belong to all types of invertebrates. It is also likely that the first chordates appear - non-cranial.
Palaeozoic
It began about 570 million years ago and lasted more than 300 million years.
Paleozoic - ancient life. Starting from it, the process of evolution is better studied, since the remains of organisms from the upper geological layers are more accessible. Hence, it is customary to consider each era in detail, noting the changes in the organic world for each period (although their periods are distinguished both in the Archean and in the Proterozoic).
Cambrian Period (Cambrian)
Lasted about 70 million years. Marine invertebrates and algae thrive. Many new groups of organisms appear - the so-called Cambrian explosion occurs.
Ordovician period (Ordovician)
Lasted 60 million years. The heyday of trilobites, racoscorpions. The first vascular plants appear.
Silurian (30 Ma)
- Bloom of corals.
- The appearance of scutellum - jawless vertebrates.
- The appearance of psilophyte plants that have come to land.
Devonian (60 Ma)
- The flowering of corymbs.
- The appearance of lobe-finned fish and stegocephalians.
- Distribution on land of higher spores.
Carboniferous period
Lasted about 70 million years.
- The rise of amphibians.
- Appearance of the first reptiles.
- The emergence of flying forms of arthropods.
- Decline in the number of trilobites.
- Blossoming ferns.
- The emergence of seed ferns.
Perm (55 million)
- The spread of reptiles, the emergence of animal-toothed lizards.
- Trilobite extinction.
- Disappearance of coal forests.
- Distribution of gymnosperms.
Mesozoic era
The era of middle life. It began 230 million years ago and lasted about 160 million years.
Triassic
Duration - 35 million years. The flowering of reptiles, the appearance of the first mammals and true bony fish.
Jurassic period
Lasted about 60 million years.
- Dominance of reptiles and gymnosperms.
- Appearance of Archeopteryx.
- There are many cephalopods in the seas.
Cretaceous period (70 million years)
- The emergence of higher mammals and true birds.
- Widespread distribution of bony fish.
- Reduction of ferns and gymnosperms.
- The emergence of angiosperms.
Cenozoic era
The era of new life. It began 67 million years ago, lasts, respectively, the same amount.
Paleogene
Lasted about 40 million years.
- Appearance of tailed lemurs, tarsiers, parapithecus and dryopithecus.
- An explosion of insects.
- The extinction of large reptiles continues.
- Entire groups of cephalopods are disappearing.
- dominance of angiosperms.
Neogene (about 23.5 Ma)
dominance of mammals and birds. The first representatives of the genus Homo appeared.
Anthropogene (1.5 Ma)
Appearance of Homo sapiens species. Animal and vegetable world takes on a modern look.
New geological period
The International Stratigraphic Committee (ISC) decided at the end of 2000 - consider the time since the second quarter of 2001 as a new geological period as part of the Cenozoic era. In this regard, we have already begun to receive questions to the editorial office:
Why is this needed?
Why was the Quaternary period so short - only 1-2 million years (according to various estimates), while all previous periods lasted tens of millions of years?
What will be the name and designation of the period? (Those who read about the proposed period name ask for an explanation.)
Why exactly from the second quarter, and not from the beginning of some year?
We will try to answer these questions.
IN AND. Vernadsky believed that human activity becomes a powerful geological factor, commensurate with natural factors. The validity of this became especially evident towards the end of the 20th century. The movement of huge masses of rock during mining, artificial intervention in the geochemical and hydrogeological regimes of the earth's crust required a strict account of all this impact. Therefore, the MSC decided to record the state of the earth's crust at some point in order to keep a record of its changes as a result of technogenic impact starting from that moment. It would be logical to make this moment the beginning of 2000 or 2001, but by the beginning of 2000 they did not have time to get a clear picture of the state of the interior of the planet as a whole, and by September 2000 it turned out that the necessary documentation did not have time even by the beginning of 2001. That's the start of the second quarter.
Analyzing the geochronological table, you immediately notice that the duration of eras and periods gradually decreases as we approach the present. They wrote about the general acceleration of geological processes, but most likely this is due to the fact that we know more about later geological periods, more traces of them remain, so periodization can be done with greater fractionality. As for the most recent time, human intervention has indeed accelerated many processes.
Earlier in geology, igneous and metamorphic rocks were considered primary, sedimentary - secondary. When in the middle of the XVIII century. younger sedimentary rocks were isolated, they were called tertiary, they included the Paleogene and Neogene, which from half a century ago constituted a single tertiary system, which was formed during the eponymous tertiary period. In 1829, the "youngest" deposits were identified, they were called Quaternary; accordingly, the Quaternary period was also singled out; its second name is anthropogen, in Greek man-bearing.
Geological scale
Therefore, the MSC did not suffer for a long time with the name of the new period: without further ado, the period was called fivefold, or technogenic(however, here the connotation is somewhat different: not “giving birth to technology”, but “born by technology”). The Quaternary period is denoted by the symbol Q (Latin quartus- fourth). Fivefold wanted to be called by analogy quintus(fifth), but they realized it in time: they would have to designate it with the same letter Q, only, probably, crossed out, like the crossed out P - this is the Paleogene (not to be confused with the Permian), the crossed out C - the Cambrian (unlike the Carboniferous); everyone who has typed these characters on a typewriter, and especially on a computer, knows how inconvenient it is. We decided to take as a basis not Latin, but English or German and designate the period F ( five or fu..nf), there is a blessing and a precedent: the Cretaceous period is denoted by the letter K from the German Kreide- a piece of chalk.
Now all states are obliged to submit to the MSC every 5 years a report on the volume of mining operations, on which rocks, in what quantity, and from where they were moved, where they formed strata of fivefold, or technogenic, deposits. In Russian terminology, that's right - technogenic. The deposits and landforms formed by man are called anthropogenic, and the deposits and forms formed by any processes during the Quaternary period, or the Anthropogen, are called Anthropogenic. Hence it follows that the rocks formed in the fivefold period in a natural way, without human intervention, can also be called technogenic.
In a word, a very serious decision has been made. How effective will be its results, time will tell.
The longest geological period on the planet
Approximately 2500 million years ago, the Archaean was replaced by a new eon - the Proterozoic. And it was he who subsequently became the longest geological period in the history of our planet, lasting almost 2000 million years and including three long eras: Paleoproterozoic, Mesoproterozoic and Neoproterozoic, during which significant changes took place on the Earth.
Dividing the history of the Earth into eras and periods
And the first significant event that occurred at the beginning of the longest geological period on the planet, or rather in the era of the Paleoproterozoic, the siderian period, that is, about 2.4 billion years ago, is, of course, an oxygen catastrophe, which entailed significant changes in the composition of the atmosphere . So, it was in the earliest geological period of the Proterozoic, due to the extinction of the activity of oceanic and terrestrial volcanoes, that the biochemical composition of the world ocean began to change completely, as a result of which oxygen, released by already existing cyanobacteria, began to be produced even more rapidly, leaving local pockets and oxidizing all around. Upon completion of the oxidation process, the atmosphere finally began to be enriched with free oxygen, and it was this factor that led to a cardinal change in the composition of the atmosphere. It is noteworthy that there is no exact data on its original composition, and the fact that everything changed after the oxygen catastrophe is evidenced by the found ancient rocks that have not undergone oxidation processes.
After these events, the world was literally “turned inside out”, because if earlier it was filled with anaerobic microorganisms that could exist exclusively outside the oxygen environment, pushing aerobic microorganisms into local pockets, then a gradual increase in the level of oxygen in the atmosphere led to the opposite picture. However, this does not mean at all that the rapidly changing atmosphere even remotely resembled the modern one, because only 400 million years after the start of the oxygen catastrophe, the content of free oxygen in its composition reached ten percent of the volume of O2 that can be observed today (this milestone was called the point Pasteur). It is noteworthy that it was previously believed that this figure was exactly 10 times less, however, as it turned out later, both figures were quite enough to ensure the full functioning of rapidly multiplying unicellular organisms. Nevertheless, these processes entailed another colossal test for the planet - the ice age, which developed as a result of the massive absorption of methane by rapidly released free oxygen.
And although at that time the luminosity of the Sun for our planet increased by as much as 6 percent on average, it could not warm up due to a shortage of methane, which is capable of producing powerful Greenhouse effect, according to one theory, ice covered the entire Earth, literally turning it into a giant snowball. It is noteworthy that by that period the volume of the world ocean that exists in modern times had already formed, and after the end of the Huron glaciation period, which occurred approximately 2.1 billion years ago, more complex organisms in the form of sponges and fungi began to appear on Earth.
In addition, the soil began to actively form, the main role in this process was played by the vital activity of bacteria and unicellular algae, now known as prokaryotes. Another significant event in this era of the Earth's existence was the first relative stabilization of the continents, as a result of which the once-existing super-continent Rodinia began to form, although it was far from the only one in its entire history. The end of the formation of this formation is approximately dated to 1150 million years BC, but by the end of the Proterozoic it again disintegrated.
In fact, Rodinia existed for no more than 250 million years, and after the collapse, about 8 large fragments remained from it, which later became the basis for modern continents. During this period, complex organisms already existed on the planet, as evidenced by their numerous remains. Unfortunately, the collapse of the super-continent was not the last test for the Earth of the Paleozoic era, because soon its surface was again covered with ice, which claimed hundreds of thousands of lives of animals that had appeared by that time.
It is noteworthy that the found remains of animals, most likely dead from another global cooling, had a solid skeleton. This fact indicates that evolution during the Proterozoic period was striking in the scale of its development.
The history of the development of the Earth for the convenience of study is divided into four eras and eleven periods. The two most recent periods are in turn divided into seven systems or eras.
The earth's crust is stratified, i.e. the various rocks that make it up lie on top of each other in layers. As a rule, the age of rocks decreases towards the upper layers. The exception is the areas with disturbed due to the movements of the earth's crust, the occurrence of layers. William Smith in the 18th century noticed that during the geological periods of time, some organisms have significantly advanced in their structure.
According to modern estimates, the age of the planet Earth is approximately 4.6 - 4.9 10 years. These estimates are based mainly on the study of rocks by radiometric dating methods.
ARCHEUS. Not much is known about life in the Archean. The only animal organisms were cellular prokaryotes - bacteria and blue-green algae. The products of the vital activity of these primitive microorganisms are also the most ancient sedimentary rocks (stromatolites) - calcareous formations in the form of pillars, found in Canada, Australia, Africa, the Urals, and Siberia. Sedimentary rocks of iron, nickel, manganese have a bacterial basis. Many microorganisms are active participants in the formation of colossal, as yet little explored mineral resources at the bottom of the World Ocean. The role of microorganisms is also great in the formation of oil shale, oil and gas.
Geological table of the Earth
Blue-green, bacteria quickly spread in the Archaean and become the masters of the planet. These organisms did not have a separate nucleus, but a developed metabolic system, the ability to reproduce. Blue-green, in addition, possessed the apparatus of photosynthesis. The appearance of the latter was the largest aromorphosis in the evolution of living nature and opened one of the ways (probably specifically terrestrial) for the formation of free oxygen.
By the end of the Archean (2.8-3 billion years ago), the first colonial algae appeared, the fossilized remains of which were found in Australia, Africa, etc.
The most important stage in the development of life on Earth is closely related to the change in the concentration of oxygen in the atmosphere, the formation of the ozone screen. Thanks to the vital activity of blue-greens, the content of free oxygen in the atmosphere has increased markedly. The accumulation of oxygen led to the emergence of a primary ozone screen in the upper layers of the biosphere, which opened horizons for flourishing.
PROTEROZOI. Proterozoic - a huge stage in duration historical development Earth. During its course, bacteria and algae reach an exceptional flowering, with their participation, the processes of sedimentation were intensively going on. As a result of the vital activity of iron bacteria in the Proterozoic, the largest iron ore deposits were formed.
At the turn of the early and middle Riphean, the dominance of prokaryotes is replaced by the flourishing of eukaryotes - green and golden algae. From unicellular eukaryotes, multicellular ones with a complex organization and specialization develop in a short time. The oldest representatives of multicellular animals have been known since the late Riphean (700-600 million years ago).
Now we can state that 650 million years ago, the earth's seas were inhabited by a variety of multicellular organisms: solitary and colonial polyps, jellyfish, flatworms, and even the ancestors of modern annelids, arthropods, molluscs and echinoderms. Some forms of fossil animals are now difficult to assign to known classes and types. Among plant organisms at that time, unicellular organisms predominated, but multicellular algae (green, brown, red), fungi also appear.
PALEOZOIC. By the beginning of the Paleozoic era, life had passed perhaps the most important and difficult part of its journey. Four kingdoms of living nature were formed: prokaryotes, or pellets, mushrooms, green plants, animals.
The ancestors of the kingdom of green plants were unicellular green algae, common in the seas of the Proterozoic. Along with floating forms among the bottoms, there appeared those attached to the bottom. A fixed lifestyle required the dismemberment of the body into parts. But the acquisition of multicellularity, the division of a multicellular body into parts that perform various functions, turned out to be more promising.
Of decisive importance for further evolution was the emergence of such an important aromorphosis as the sexual process.
How and when did the division of the living world into plants and animals occur? Do they have the same root? Disputes of scientists around this issue do not subside even today. Perhaps the first animals evolved from a common stem of all eukaryotes or from single-celled green algae.
CAMBRIAN- flowering of skeletal invertebrates. During this period, another period of mountain building took place, the redistribution of land and sea area.
The climate of the Cambrian was temperate, the continents were unchanged. Only bacteria and blue-greens still lived on land. The seas were dominated by green and brown algae attached to the bottom; diatoms, golden algae, and euglena algae swam in the water column.
As a result of the increase in the washout of salts from the land, marine animals have been able to absorb mineral salts in large quantities. And this, in turn, opened up wide ways for them to build a rigid skeleton.
The most widespread were the most ancient arthropods - trilobites, outwardly similar to modern crustaceans - wood lice.
Very characteristic of the Cambrian is a peculiar type of multicellular animals - the archaeocyath, which died out by the end of the period. A variety of sponges, corals, brachiopods, and mollusks also lived at that time. Later, sea urchins appeared.
ORDOVIC. In the seas of the Ordovician, green, brown and red algae, numerous trilobites were diversely represented. In the Ordovician, the first cephalopods, relatives of modern octopuses and squids, appeared, and brachiopods, gastropods, spread. There was an intensive process of formation of reefs by four-beam corals and tabulates. Graptolites are widely used - hemichordates, combining the features of invertebrates and vertebrates resembling modern lancelets.
In the Ordovician, spore plants appeared - psilophytes, growing along the banks of fresh water bodies.
SILUR. The warm shallow seas of the Ordovician were replaced by large areas of land, which led to the drying up of the climate.
In the Silurian seas, graptolites lived out their lives, trilobites fell into decline, but cephalopods reached exceptional prosperity. Corals gradually replaced the archaeocyath.
In the Silurian, peculiar arthropods developed - giant crustaceans, reaching up to 2 m in length. By the end of the Paleozoic, the entire group of crustaceans almost died out. They resembled a modern horseshoe crab.
A particularly noteworthy event of this period was the appearance and distribution of the first representatives of vertebrates - armored "fish". These “fishes” only resembled real fish in shape, but belonged to another class of vertebrates - jawless or cyclostomes. They could not swim for a long time and mostly lay at the bottom of bays and lagoons. Due to a sedentary lifestyle, they were incapable of further development. Of the modern representatives of cyclostomes, lampreys and hagfishes are known.
A characteristic feature of the Silurian period is the intensive development of terrestrial plants.
One of the first terrestrial, or rather amphibious, plants were psilophytes, leading their lineage from green algae. In reservoirs, algae adsorb water and substances dissolved in it over the entire surface of the body, which is why they do not have roots, and the outgrowths of the body, resembling roots, serve only as attachment organs. In connection with the need to conduct water from the roots to the leaves, a vascular system arises.
The emergence of plants on dry land is one of the greatest moments of Evolution. It was prepared by the previous evolution of the organic and inorganic world.
DEVONIAN. Devon - the period of fish. The climate of the Devonian was more sharply continental, icing occurred in the mountainous regions of South Africa. In warmer regions, the climate changed towards greater desiccation, desert and semi-desert areas appeared.
In the seas of the Devonian, fish reached great prosperity. Among them were cartilaginous fish, fish with a bone skeleton appeared. According to the structure of the fins, bony fish are divided into ray-finned and lobe-finned. Until recently, it was believed that the crossopterans became extinct at the end of the Paleozoic. But in 1938, a fishing trawler delivered such a fish to the East London Museum and it was named coelacanth.
At the end of the Paleozoic, the most significant stage in the development of life was the conquest of land by plants and animals. This was facilitated by the reduction of sea basins, the rise of land.
Typical spore plants emerged from psilophytes: club mosses, horsetails, ferns. On the earth's surface the first forests appeared.
By the beginning of the Carboniferous, there was a noticeable warming and humidification. In the vast valleys and tropical forests, in the conditions of continuous summer, everything grew rapidly upwards. Evolution has opened a new way - reproduction by seeds. Therefore, gymnosperms picked up the evolutionary baton, and spore plants remained a side branch of evolution and receded into the background.
The emergence of vertebrates on land occurred in the late Devonian period, after the land conquerors - psilophytes. At this time, the air was already mastered by insects, and the descendants of lobe-finned fish began to spread over the earth. The new way of transportation allowed them to move away from the water for some time. This led to the emergence of creatures with a new way of life - amphibians. Their most ancient representatives - ichthyoskhegi - were found in Greenland in Devonian sedimentary rocks.
The heyday of ancient amphibians is dated to the Carboniferous. It was during this period that stegocephals were widely developed. They lived only in the coastal part of the land and could not conquer the inland massifs located far from water bodies.
Geological scale. time, showing the sequence and subordination of the stages of development of the earth's crust and organic. the world of the Earth (eons, eras, periods, epochs, centuries). The sequence of deposits is reflected in the so-called. stratigraphic scale, units to swarm ... ... Biological encyclopedic Dictionary
- (a. geological dating, geochronological scale; n. geologische Zeitrechnung; f. echelle geochronologique; i. escala geocronologica) follow. a number of geochronological equivalents of common stratigraphic. subdivisions and their taxonomic ... ... Geological Encyclopedia
geochronological scale- — Topics oil and gas industry EN geologic time scale …
See Art. Geochronology… Great Soviet Encyclopedia
Geochronological scale of the Phanerozoic- (duration 570 million years) Eras and their duration Periods Beginning of periods, million years ago Duration of periods, million years Development of life Cenozoic (67 million years) Anthropogenic Development of mankind. Neogene Appearance of man ... ... Beginnings of modern natural science
geochronological scale- The scale of geological time, showing the sequence and subordination of the main stages of the geological history of the Earth and the development of life on it. [Glossary of geological terms and concepts. Tomsk State University] Topics geology… Technical Translator's Handbook
Scale of relative geol. time, showing the sequence and subordination of the main stages of geol. the history of the Earth and the development of life on it. It is the result of the analysis and synthesis of all data of the stratigraphic scale and, accordingly ... ... Geological Encyclopedia
Cox, Doell, Dalrymple, 1968, based on the reversals of the Earth's magnetic field that have repeatedly occurred in geol. past. Developed for the last 4.5 million years of the Cenozoic. The main units of the Sh. G. p. are epochs (lasting about 1 1.5 million years ... Geological Encyclopedia
geochronological scale- geochronological scale geological dating, geochronological scale geologische Zeitrechnung last series of geochronological equivalents of global stratigraphic subdivisions and their taxonomic agility. First geochronological scale for ... ... Girnichiy encyclopedic dictionary
Age of some areas on the Moon: 1 Age of craters (a Nectar, b Imbrian, c Eratosthenes, d Copernican) 2 Age of the seas (a Prenectar, b Nectar, c Early ... Wikipedia
Books
- Earth is a restless planet: Atmosphere, hydrosphere, lithosphere: A book for schoolchildren ... and not only, Tarasov L.V. The book describes in an interesting and intelligible way…
- Visual Encyclopedia. All about the planet Earth and its inhabitants,. A detailed description of the history of the Earth from big bang to the present day. Hundreds of color illustrations. Latest data, explanatory diagrams and drawings. Geochronological time scale. Wide view…
Stages of development of the planet. Of great importance for geographical science is the ability to determine the age of the Earth and the earth's crust, as well as the time of significant events that occurred in the history of their development. The history of the development of the planet Earth is divided into two stages: planetary and geological.
planetary stagecovers the period of time from the birth of the Earth as a planet to the formation of the earth's crust. The scientific hypothesis about the formation of the Earth (as a cosmic body) appeared on the basis of general views on the origin of other planets that make up the solar system. You know that the Earth is one of the 8 planets of the solar system from the 6th grade course. Planet Earth was formed 3.5-5 billion years ago. This stage ended with the appearance of the primary lithosphere, atmosphere and hydrosphere (3.7-3.8 billion years ago).
Geological stagebegan with the appearance of the first rudiments of the earth's crust, which continues to the present. During this period, various rocks were formed. The earth's crust has repeatedly been subjected to slow ups and downs under the influence of internal forces. During periods of subsidence, the territories were flooded with water and sedimentary rocks (sands, clays, etc.) were deposited at the bottom, and during periods of uplift of the sea bottom, plains formed here, composed of these sedimentary rocks.
Thus, the original structure of the earth's crust began to change. This process continued uninterrupted. At the bottom of the seas and depressions of the continents, a sedimentary layer of rocks accumulated, among which were the remains of plants and animals. Each geological period corresponds to their specific 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, methods of relative and absolute chronology (geochronology) are used.
To determine relative age of rocks, it is necessary to know the patterns of successive occurrence of layers of sedimentary rocks of different composition. Their essence is as follows: if the layer of sedimentary rocks lies in an undisturbed state, as they were deposited one after another on the bottom of the moraines, then this means that the layer lying below was deposited earlier, and the layer lying above was formed later, therefore, he is younger.
Indeed, if there is no lower layer, then it is clear that the one covering it upper layer cannot be formed, so the lower the sedimentary layer, the greater its age. The topmost layer is considered the youngest.
In determining the relative age of rocks great importance has the study of the successive occurrence of sedimentary rocks of different composition and the fossilized remains of animal and plant organisms contained in them. As a result of the painstaking work of scientists to determine the geological age of rocks and the time of development of plant and animal organisms, a geochronological table was compiled. It was approved at the II International Geological Congress in 1881 in Bologna. It is based on the stages of life development identified by paleontology. This table-scale is constantly being improved. The current state of the table is given on p. 45.
The scale units are era. They are divided into periods, which are subdivided into era. The five largest of these divisions (eras) bear names associated with the nature of the life that existed then. For example, ar-hey- early life time p[utherozoic- the era of primary life, Paleozoic- the era of ancient life, mesozoic- the era of middle life, Cenozoic - era of new life.
Eras are subdivided into shorter periods of time - periods(sometimes called systems). Their names are different. Some of them come from the names of rocks that are most characteristic of this time (for example carbonic period in the Paleozoic and Cretaceous in the Mesozoic). Most of the periods are named after those localities in which the deposits of a particular period are most fully represented and where these deposits were first characterized. Ancient period Paleozoic - Cambrian got its name from the Cambrian - an ancient state in the west of England. Names of the next periods leozoic - Ordovician and Silurian- come from the names of the ancient tribes of the Ordovicians and Silures, who inhabited the territory of present-day Wales.
To distinguish between the systems of the geochronological table, conventional signs are adopted. Geological eras are indicated by indices (signs) - the initial letters of their Latin names (for example, archaean - AR ), and period indices - by the first letter of their Latin names (for example, Permian P).
Definition absolute age of rocks began at the beginning of the 20th century, after the law of decay of radioactive elements was discovered. Its essence is as follows. In the bowels of the Earth are radioactive elements, such as uranium. Over time, it slowly, at a constant rate, decays into helium and lead. The helium dissipates, while the lead remains in the rock. Knowing the decay rate of uranium (out of 100 g of uranium, 1 g of lead is released over 74 million years), it is possible to calculate how many years ago it was formed by the amount of lead contained in the rock.
The use of radiometric methods made it possible to determine the age of many rocks that make up the earth's crust. Thanks to these studies, it was possible to establish the geological and planetary age of the Earth. Based on the relative and absolute methods of reckoning, a geochronological table was compiled.
1. What stages is the geological history of the Earth's development divided into?
2. What stage of the development of the Earth is geological?
3*. How is the relative and absolute age of rocks determined?
1. Compare the duration of geological eras and periods according to the geochronological table.