Stratigraphic scale (geochronological) is a standard by which the history of the Earth is measured in terms of time and geological magnitude. This scale is a kind of calendar that counts time intervals in hundreds of thousands and even millions of years.
About the planet
Modern conventional wisdom about the Earth is based on various data, according to which the age of our planet is approximately four and a half billion years. Neither rocks nor minerals that could indicate the formation of our planet have yet been found either in the bowels or on the surface. Refractory compounds rich in calcium, aluminum and carbonaceous chondrites, which were formed in the solar system before anything else, limit the maximum age of the Earth to these figures. The stratigraphic scale (geochronological) shows the boundaries of time from the formation of the planet.
A variety of meteorites were studied using modern methods, including uranium-lead, and as a result, estimates of the age of the Solarsystems. As a result, the time that has elapsed since the creation of the planet was divided into time intervals according to the most important events for the Earth. The geochronological scale is very convenient for tracking geological times. The eras of the Phanerozoic, for example, are delimited by major evolutionary events when the global extinction of living organisms took place: the Paleozoic on the border with the Mesozoic was marked by the largest extinction of species in the entire history of the planet (Permo-Triassic), and the end of the Mesozoic is separated from the Cenozoic by the Cretaceous-Paleogene extinction.
History of Creation
For the hierarchy and nomenclature of all modern divisions of geochronology, the nineteenth century turned out to be the most important: in its second half, the sessions of the IGC - the International Geological Congress took place. After that, from 1881 to 1900, a modern stratigraphic scale was compiled.
Its geochronological "stuffing" was later repeatedly refined and modified as new data became available. Quite different signs have served as themes for specific names, but the most common factor is geographical.
Names
For example, the Cambrian period is named so because Cambria is Wales during 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 Yura. The ancient tribes - the Lusatian Serbs (the Germans called them Wends), served as the name of the Vendian period, and in memory of the Celts - the Ordovician and Silurian tribes - were namedSilurian and Ordovician periods.
The geochronological scale sometimes associates names with the geological composition of rocks: the Carboniferous one appeared due to the huge number of coal seams during excavations, and the Cretaceous one simply because writing chalk spread around 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, is of little importance to geologists. The entire life of our planet was divided into two main segments - Phanerozoic and Cryptozoic (Precambrian), which are delimited by the appearance of fossil remains in sedimentary rocks.
Cryptose is a most interesting time, absolutely hidden from us, since the soft-bodied organisms that existed then did not leave a single trace in sedimentary rocks. Periods of the geochronological scale, such as the Ediacaran and Cambrian, appeared in the Phanerozoic through the research of paleontologists: they found in the rock a large variety of mollusks and many species of other organisms. Findings of fossil fauna and flora allowed them to dissect the strata and give them the appropriate names.
Time Slots
The second largest division is an attempt to designate the historical intervals of the life of the Earth, when the four main periods were divided by the geochronological scale. The table shows them as primary (Precambrian), secondary (Paleozoic and Mesozoic), tertiary (almost the entire Cenozoic) and Quaternary - a period that isin a special position, because although it is the shortest, it is replete with events that have left vivid and well-read traces.
Now, for convenience, the geochronological scale of the Earth is divided into 4 eras and 11 periods. But the last two of them are divided into 7 more systems (epochs). No wonder. It is the last segments that are especially interesting, since this geological period corresponds to the time of the appearance and development of mankind.
Major milestones
Over four and a half billion years in the history of the Earth, the following events have occurred:
- Pre-nuclear organisms (the first prokaryotes) appeared - four billion years ago.
- The ability of organisms to photosynthesis was discovered - three billion years ago.
- Cells with a nucleus (eukaryotes) appeared - two billion years ago.
- Multicellular organisms evolved - one billion years ago.
- Insect ancestors appeared: the first arthropods, arachnids, crustaceans and other groups - 570 million years ago.
- Fish and proto-amphibians are five hundred million years old.
- Land plants have appeared and have delighted us for 475 million years.
- Insects have lived on earth for four hundred million years, and plants have received seeds in the same time period.
- Amphibians have been living on the planet for 360 million years.
- Reptiles (reptiles) appeared three hundred million years ago.
- Two hundred million years ago, the first mammals began to evolve.
- One hundred and fifty million years ago - the first birdstried to master the sky.
- Flowers (flowering plants) bloomed one hundred and thirty million years ago.
- Sixty-five million years ago, the Earth lost the dinosaurs forever.
- Two and a half million years ago a man (genus Homo) appeared.
- One hundred thousand years have passed since the beginning of anthropogenesis, thanks to which people have acquired their current appearance.
- Neanderthals have not existed on Earth for twenty-five thousand years.
The geochronological scale and the history of the development of living organisms, merged together, albeit somewhat schematically and generally, with rather approximate dates, but the concept of the development of life on the planet is clearly presented.
Rock bedding
Earth's crust is mostly stratified (where there is no disruption due to earthquakes). The general geochronological scale is drawn up according to the location of rock strata, which clearly show how their age decreases from lower to upper.
Fossils also change as you move up: they become more complex in their structure, some undergo significant changes from layer to layer. This can be observed without visiting paleontological museums, but simply by going down the subway - on facing granite and marble, eras very distant from us left their imprints.
Anthropogen
The last period of the Cenozoic era is the modern stage of the earth's history,including the Pleistocene and Holocene. What just didn’t happen in these turbulent millions of years (specialists still think differently: from six hundred thousand to three and a half million). There were repeated changes of cooling and warming, huge continental glaciations, when the climate was humidified south of the advancing glaciers, water basins appeared, both fresh and s alty. Glaciers absorbed part of the World Ocean, the level of which dropped by a hundred or more meters, due to which continents were formed.
Thus, there was an exchange of fauna, for example, between Asia and North America, when a bridge was formed instead of the Bering Strait. Closer to the glaciers, cold-loving animals and birds settled: mammoths, hairy rhinos, reindeer, musk oxen, arctic foxes, polar partridges. They spread to the south very far - to the Caucasus and the Crimea, to Southern Europe. Along the course of the glaciers, relict forests are still preserved: pine, spruce, fir. And only at a distance from them did deciduous forests grow, consisting of trees such as oak, hornbeam, maple, beech.
Pleistocene and Holocene
This is the era after the ice age - not yet completed and not fully lived segment of the history of our planet, which indicates the international geochronological scale. Anthropogenic period - Holocene, is calculated from the last continental glaciation (northern Europe). It was then that the land and the World Ocean received their modern outlines, and all the geographical zones of the modern Earth also took shape. The predecessor of the Holocene, the Pleistocene, is the first epoch of anthropogenicperiod. The cooling that began on the planet continues - the main part of the specified period (Pleistocene) was marked by a much colder climate than the modern one.
The northern hemisphere is experiencing the last glaciation - thirteen times the surface of the glaciers exceeded modern formations even in interglacial periods. Pleistocene plants are closest to modern ones, but they were located somewhat differently, especially during periods of glaciation. The genera and species of the fauna changed, those that adapted to the Arctic form of life survived. The southern hemisphere did not recognize such huge upheavals, so Pleistocene plants and animals are still present in many forms. It was in the Pleistocene that the evolution of the genus Homo took place - from Homo habilis (archanthropes) to Homo sapiens (neoanthropes).
When did mountains and seas appear?
The second period of the Cenozoic era - the Neogene and its predecessor - the Paleogene, including the Pliocene and Miocene about two million years ago, lasted about sixty-five million years. In the Neogene, the formation of almost all mountain systems was completed: the Carpathians, the Alps, the Balkans, the Caucasus, the Atlas, the Cordillera, the Himalayas, and so on. At the same time, the outlines and sizes of all sea basins changed, since they were subjected to severe drying. It was then that Antarctica and many mountainous areas were frozen.
Marine inhabitants (invertebrates) have already become close to modern species, and mammals dominated on land - bears, cats, rhinos, hyenas, giraffes, deer. Great apes develop so much that a little later (in the Pliocene) they were able toaustralopithecines appear. On the continents, mammals lived separately, since there was no connection between them, but in the late Miocene, Eurasia and North America nevertheless exchanged fauna, and at the end of the Neogene, the fauna migrated from North America to South America. It was then that the tundra and taiga were formed in the northern latitudes.
Paleozoic and Mesozoic eras
The Mesozoic precedes the Cenozoic era and lasted 165 million years, including the Cretaceous, Jurassic and Triassic periods. At this time, mountains were intensively formed on the peripheries of the Indian, Atlantic and Pacific oceans. Reptiles began their dominance on land, in water, and in the air. At the same time, the first, still very primitive mammals appeared.
Paleozoic is located on the scale before the Mesozoic. It lasted about three hundred and fifty million years. This is the time of the most active mountain building and the most intensive evolution of all higher plants. Almost all known invertebrates and vertebrates of various types and classes formed then, but there were no mammals and birds yet.
Proterozoic and Archean
The Proterozoic era lasted about two billion years. At this time, the processes of sedimentation were active. Blue-green algae developed well. There was no opportunity to learn more about these distant times.
Archaean is the oldest era in the recorded history of our planet. It lasted for about a billion years. As a result of active volcanic activity, the very firstlive microorganisms.
