The stratigraphic scale (geochronological) is a standard with which the Earth’s history is measured in terms of time and geological value. This scale is a kind of calendar that counts time intervals in hundreds of thousands and even millions of years.
About the planet
Current generally accepted ideas about the Earth are 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 testify to the formation of our planet have so far been found neither in the bowels nor on the surface. Refractory compounds rich in calcium, aluminum and carbonaceous chondrites, which were formed in the Solar system earlier than anything else, limit the maximum age of the Earth to these numbers. The stratigraphic scale (geochronological) shows the boundaries of time from the formation of the planet.
A variety of meteorites were investigated using modern methods, including uranium-lead, and as a result, estimates of the age of the solar system are presented. As a result, the time elapsed since the creation of the planet was delimited into time intervals for the most important events for the Earth. The geochronological scale is very convenient for tracking geological times. The Phanerozoic eras, for example, are demarcated by major evolutionary events when there was a global extinction of living organisms: the Paleozoic on the border with the Mesozoic was marked by the largest species extinction (Permo-Triassic) in the history of the planet, 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 divisions of geochronology, the nineteenth century turned out to be the most important: in its second half sessions of the International Geological Congress — the International Geological Congress — took place. After that, from 1881 to 1900, a modern stratigraphic scale was compiled.
Its geochronological “filling” was subsequently refined and modified several times as new data became available. Absolutely different attributes served as themes for specific names, but the most common factor is geographical.
Names
For example, the Cambrian period is so named because Cambria is Wales during the time of the Roman Empire, and the Devonian period is named after the county of Devonshire in England. The name of the Permian period came from the city of Perm, and the Jurassic was given the name of Mount Jura. Ancient tribes - Luga Serbs (Germans called them Vendians), served as the name of the Vendian period, and in memory of the Celts - tribes of the Ordovician and Silurians - the Silurian and Ordovician periods were named .
The geochronological scale sometimes connects the names with the geological composition of the rocks: coal appeared in connection with a huge number of coal seams during excavations, and chalk - simply because written chalk spread in 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 matter much to geologists. All the life time of our planet was divided into two main segments - phanerozoic and cryptose (Precambrian), which are distinguished by the appearance of fossil remains in sedimentary rocks.
Cryptose is an interesting time, absolutely hidden from us, since the then soft-bodied organisms did not leave a single trace in sedimentary rocks. Periods of the geochronological scale, such as the ediacium and the Cambrian, appeared in the Phanerozoic through the research of paleontologists: they found a large number of various mollusks and many species of other organisms in the breed. Findings of fossil fauna and flora allowed them to divide the strata and give them the corresponding names.
Time intervals
The second largest division is an attempt to indicate the historical intervals of the Earth's life, when the geochronological scale divided the four main periods. 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 vivid and well-read traces.
Now for convenience, the Earth’s geochronological scale is divided into 4 eras and 11 periods. But the last two of them are divided into 7 more systems (eras). No wonder. Especially interesting are the last segments, since this geological period 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:
- There were pre-nuclear organisms (the first prokaryotes) - 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 developed - one billion years ago.
- The ancestors of insects appeared: the first arthropods, arachnids, crustaceans, and other groups - 570 million years ago.
- Fishes and proto-amphibians - they are five hundred million years old.
- Terrestrial plants have appeared and have been pleasing us for 475 million years.
- Insects live 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 develop.
- One hundred and fifty million years ago - the first birds tried to master the sky.
- One hundred thirty million years ago flowers (flowering plants) bloomed.
- Sixty-five million years ago, the Earth forever lost dinosaurs.
- Two and a half million years ago a man appeared (genus Homo).
- One hundred thousand years have passed since the beginning of anthropogenesis, thanks to which people have acquired their present appearance.
- Twenty-five thousand years, Neanderthals do not exist on Earth.
The geochronological scale and the history of the development of living organisms, merged together, albeit somewhat schematically and generalized, with fairly approximate dates, but they provide a clear idea of the development of life on the planet.
Bedding
The earth's crust is mostly stratified (where there have been no disturbances in the strata due to earthquakes). The general geochronological scale is compiled according to the location of the rock formations, 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 the paleontological museums, but simply by going down the subway - on the facing granite and marble left their imprints quite distant from us era.
Anthropogen
The last period of the Cenozoic era is the modern stage of earthly history, including the Pleistocene and Holocene. What just did not happen in these turbulent millions of years (experts still think differently: from six hundred thousand to three and a half million). There were repeated changes in cooling and warming, huge continental glaciations, when the climate was moistened south of the approaching glaciers, water basins appeared, both fresh and salty. The glaciers absorbed part of the oceans, the level in which decreased by a hundred or more meters, due to which compounds of the continents 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 ox, Arctic fox, and partridge. They spread to the south very far - to the Caucasus and Crimea, to southern Europe. In 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 - an incomplete and not yet fully lived segment of the history of our planet, which is denoted by the international geochronological scale. The anthropogenic period - the Holocene, is calculated from the last continental glaciation (northern Europe). It was then that land and the oceans received modern outlines, as well as all the geographical areas of modern Earth. The precursor of the Holocene - the Pleistocene is the first era of the anthropogenic period. The cold snap that has begun on the planet continues - the main part of the indicated period (Pleistocene) was marked by a much colder climate than the modern one.
The northern hemisphere is undergoing the last glaciation - thirteen times the surface of glaciers surpassed modern formations even in interglacial intervals. Pleistocene plants are the closest to modern plants, but they were located somewhat differently, especially during glaciation periods. The genera and species of fauna changed, surviving adapted to the Arctic form of life. The southern hemisphere did not recognize such huge shocks, so the plants and fauna of the Pleistocene are still present in many species. It was in the Pleistocene that the evolution of the genus Homo took place - from Homo habilis (archanthropus) to Homo sapiens (neoanthropus).
When did the mountains and the seas appear?
The second period of the Cenozoic era, 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, Atlas, Cordillera, the Himalayas, and so on. At the same time, the outlines and sizes of all marine basins changed, since it was subjected to severe drainage. It was then that Antarctica and many mountainous areas were icy.
Marine inhabitants (invertebrates) have already become close to modern species, and on land mammals dominated - bears, cats, rhinos, hyenas, giraffes, deer. Human 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, the fauna still exchanged, and at the end of the Neogene from North America the fauna migrated to the South. It was then that the tundra and taiga formed in the northern latitudes.
Paleozoic and Mesozoic era
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 periphery of the Indian, Atlantic and Pacific oceans. Reptiles began their dominance on land, and in water, and in the air. Then the first, still very primitive mammals appeared.
The Paleozoic is located on a scale in front of 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 different types and classes were formed then, but mammals and birds did not exist.
Proterozoic and Archean
The Proterozoic era lasted about two billion years. At this time, the processes of sedimentation were active. Well developed blue-green algae. Learn more about these distant times the opportunity did not present itself.
Archean is the oldest era in the documented history of our planet. It lasted about a billion years. As a result of active volcanic activity, the very first living microorganisms appeared.