Geological reckoning and geochronological table
Great value for geographical science has the ability to determine the age of the earth and 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.
The planetary stage covers the period of time from the birth of the Earth as a planet to the formation of the earth's crust. The scientific hypothesis about the formation of the Earth (as a cosmic body) appeared on the basis of general views on the origin of other planets that make up solar system. The fact that the Earth is one of the 9 planets of the solar system, you know from the 6th grade course. Planet Earth was formed 4.5-4.6 billion years ago. This stage ended with the appearance of the primary lithosphere, atmosphere and hydrosphere (3.7-3.8 billion years ago).
From the moment the first rudiments of the earth's crust appeared, a geological stage began, which continues to the present. 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 the period of subsidence, the territory was flooded with water and sedimentary rocks (sands, clays, etc.) were deposited at the bottom, and during periods of sea rise, they receded and a plain formed by these sedimentary rocks arose in their place.
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 one could find the remains of plants and animals. Each geological period corresponds to their certain types 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 the 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 layers of sedimentary rocks lie in an undisturbed state as they were deposited one after another on the bottom of the seas, then this means that the layer lying below was deposited earlier, and the layer lying above was formed later, therefore he 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 a 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. Current state the table is given on p. 43.
The units of the scale are eras, divided into periods which are subdivided into eras. The five largest of these divisions - eras - bear names associated with the nature of the life that existed then. For example, the Archean is the time of earlier life, the Proterozoic is the era of primary life, the Paleozoic is the era of ancient life, the Mesozoic is the era of middle life, and the Cenozoic is the era of new life.
Eras are subdivided into shorter periods of time - periods. Their names are different. Some of them come from the names of rocks that are most characteristic of this time (for example, the Carboniferous period in the Paleozoic and the Mole period in the Mesozoic). Most of the periods are named after those localities in which the deposits of a particular period are most fully developed and where these deposits were first characterized. Ancient period Paleozoic - Cambrian - got its name from the Cambrian - ancient state in the west of England. The names of the following periods of the Paleozoic - Ordovician and Silurian - come from the names of the ancient tribes of the Ordovicians and Silurians, who inhabited the territory of 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).
The determination of the absolute age of rocks began at the beginning of the 20th century, after scientists discovered the law of decay of radioactive elements. In the 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), by the amount of lead contained in the rock, one can calculate how many years ago it was formed.
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 age of rocks determined?
4. Compare the duration of geological eras and periods according to the geochronological table.
Hello! In this article I want to tell you about the geochronological column. This is a column of periods of the Earth's evolution. And also more about each era, thanks to which you can draw a picture of the formation of the Earth throughout its history. What types of life first appeared, how did they change, and how much did it take.
The geological history of the Earth is divided into large intervals - eras, eras are divided into periods, periods are divided into epochs. Such a division was associated with events that took place on. The change in the abiotic environment influenced the evolution of the organic world on Earth.
Geological eras of the Earth, or geochronological scale:
And now about everything in more detail:
Designations:
eras;
periods;
Epochs.
1. Catharchean era (from the creation of the Earth, about 5 billion years ago, to the origin of life);
2. Archean era , the most ancient era (3.5 billion - 1.9 billion years ago);
3. Proterozoic era (1.9 billion - 570 million years ago);
Archean and Proterozoic are still combined into Precambrian. The Precambrian covers the largest part of geological time. Formed, areas of land and sea, active volcanic activity took place. Shields of all continents were formed from Precambrian rocks. Traces of life are usually rare.
4. Palaeozoic (570 million - 225 million years ago) with such periods :
Cambrian period(from the Latin name for Wales)(570 million - 480 million years ago);
The transition to the Cambrian is marked by the unexpected appearance of a huge number of fossils. This is a sign of the beginning of the Paleozoic era. Marine life flourished in numerous shallow seas. Trilobites were especially widespread.
Ordovician period(from the British Ordovician tribe)(480 million - 420 million years ago);
On a significant part of the Earth it was soft, most of the surface was still covered by the sea. The accumulation of sedimentary rocks continued, mountain building took place. There were reef builders. An abundance of corals, sponges and molluscs has been noted.
Silurian (from the British Silur tribe)(420 million - 400 million years ago);
Dramatic events in the history of the Earth began with the development of jawless fish (the first vertebrates), which appeared in the Ordovician. Another significant event was the appearance in the late Silurian of the first terrestrial.
Devonian (from Devonshire in England)(400 million - 320 million years ago);
In the early Devonian, mountain building movements reached their peak, but basically it was a period of spasmodic development. The first seed plants settled on land. Noted big variety and the number of fish-like, the first terrestrial animals- amphibians.
Carboniferous or Carboniferous period (from the abundance of coal in the seams) (320 million - 270 million years ago);
Mountain building, folding, and erosion continued. AT North America and the flooding of wetland forests and river deltas occurred, large coal deposits formed. The southern continents were covered by glaciation. Insects spread rapidly, the first reptiles appeared.
Permian period (from the Russian city of Perm)(270 million - 225 million years ago);
A large part of Pangea - the supercontinent that united everything - was dominated by conditions. Reptiles spread widely, modern insects evolved. A new terrestrial flora developed, including conifers. Several marine species have disappeared.
5. Mesozoic era (225 million - 70 million years ago) with such periods:
Triassic (from the tripartite division of the period proposed in Germany)(225 million - 185 million years ago);
With the advent of the Mesozoic era, Pangea began to disintegrate. On land, the dominance of conifers was established. Diversity among reptiles was noted, the first dinosaurs and giant marine reptiles appeared. Primitive mammals evolved.
Jurassic period (from mountains in Europe)(185 million - 140 million years ago);
Significant volcanic activity has been associated with the formation Atlantic Ocean. Dinosaurs dominated the land, flying reptiles and primitive birds conquered the air ocean. There are traces of the first flowering plants.
Cretaceous period (from the word "chalk")(140 million - 70 million years ago);
During the maximum expansion of the seas, chalk deposits occurred, especially in Britain. The dominance of dinosaurs continued until the extinction of them and other species at the end of the period.
6. Cenozoic era (70 million years ago - up to our time) with such periods and epochs:
Paleogene period (70 million - 25 million years ago);
— Paleocene epoch ("the oldest part of the new epoch")(70 million - 54 million years ago);
— Eocene epoch ("dawn of a new era")(54 million - 38 million years ago);
— Oligocene era ("not very new")(38 million - 25 million years ago);
Neogene period (25 million - 1 million years ago);
— Miocene epoch ("comparatively new")(25 million - 8 million years ago);
— Pliocene epoch ("very new")(8 million - 1 million years ago);
The Paleocene and Neocene periods are still combined into the Tertiary period. With the advent of the Cenozoic era (new life), there is an abrupt spread of mammals. Many large species have evolved, although many have become extinct. There has been a sharp increase in the number of flowering plants. With the cooling of the climate, herbaceous plants appeared. There has been a significant uplift.
Quaternary period (1 million - our time);
— Pleistocene era ("newest")(1 million - 20 thousand years ago);
— Holocene epoch(“a completely new era”) (20 thousand years ago - our time).
This is the last geological period that includes the present. Four major glaciations alternated with warming periods. The number of mammals has increased; they have adapted to. There was a formation of man - the future ruler of the Earth.
There are also other ways of dividing eras, epochs, periods, eons are added to them, and some epochs are still divided, like in this table, for example.
But this table is more complicated, the confusing dating of some eras is purely chronological, not based on stratigraphy. Stratigraphy is the science of determining the relative geologic age of sedimentary rocks, subdividing rock strata, and correlating different geological formations.
Such a division, of course, is relative, since there was no sharp distinction between today and tomorrow in these divisions.
But still, at the turn of neighboring eras and periods, significant geological transformations mainly took place: the processes of formation of mountains, the redistribution of seas, changing of the climate etc.
Each subsection was characterized, of course, by the originality of flora and fauna.
, and can be found in the same section.
Thus, these are the main eras of the Earth, on which all scientists rely 🙂
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 it appears a large number of living organisms with mineral skeletons. 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.
Our schools and institutes officially teach the idea that our earth is many millions of years old. To confirm this point of view, as scientific, a geochronological table is given with long eras and periods, which scientists allegedly calculated from layers of sedimentary rocks and their fossils in them. Here is an example lesson:
"Teacher: For many years, geologists, studying rocks, tried to determine the age of the Earth. But until recently they were far from successful. In the early 17th century, the Archbishop of Armagh, James Asher, calculated the date of the creation of the world from the Bible, and determined it as 4004 BC n e.
But he was wrong more than a million times. Today, scientists believe that the age of the Earth is 4600 million years. The science that studies the age of the earth by the arrangement of rocks is called geology.
(Geological table photo No. 1)
(geochronological table photo No. 2)
Students take these data on faith, trusting the word of the teacher and not checking how true this information is and whether it corresponds to reality. In fact, a lot of scientific evidence has long been known that geochronological table show invalid. There are scientists who have a different point of view on the periods of the history of our Earth. For example, the Walker Geological Model modified by Klevberg:
(Geological table photo No. 3)
I think that every person, whether he is a student or a teacher, should thoroughly double-check the official data that he receives and form his own convictions, based not on preconceived guesses, but on scientific research. To figure out which hypotheses of scientists are closer to the truth and which are not, read articles with a different point of view on the geochronological table than the official point of view taught in educational institutions.
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 a completely unclear and logical notion 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. Rocks 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 the flourishing of organic life in the seas and oceans and its emergence on 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(the era of average life) lasting 185 million years is the heyday of giant reptiles on land (giant lizards - dinosaurs, flying pterodactyls, etc.). Vegetable world and the world of insects in the Mesozoic have some features in common with our time. At this time, the first representatives of mammals and birds appear 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), replacing 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 time 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.