What is the geologic time scale? Why was it created? You will find answers to these and other questions in the article. The geochronological scale (stratigraphic scale) is the time scale of the geological history of the Earth. It is used in paleontology and geology - it is a kind of calendar for colossal time intervals.
The age of our planet
Don't you know what the geochronological scale of geological time is? Experts estimate the age of the Earth at 4.6 billion years. Minerals and rocks have been found on our planet that could be witnesses of its creation. The ultimate age of the Earth comes down to the age of the very first solid formations in our planetary system - refractory inclusions rich in aluminum and calcium (CAI) from carbonaceous chondrites.
According to the results of modern testing by the lead-uranium method, the age of CAI from the Allende meteor is 4568.5 million years. Currently, this idea of the age of the solar system is considered the most accurate. The earth could have been formed muchlater than this period - for several tens and even hundreds of millions of years.
The geologic time scale is a pretty interesting thing. The subsequent period in the history of the Earth is divided into different time intervals. Their borders touch upon the most important events that have taken place.
The boundary between the times of the Phanerozoic emerges through major evolutionary phenomena - global extinctions. The Paleozoic is separated from the Mesozoic by the largest Triassic-Permian extinction of species in the history of the Earth. The Cenozoic and Mesozoic are separated by the Cretaceous-Paleogene elimination.
History of the scale
How was the geological time scale created? The nomenclature and hierarchy of most of the current geochronological divisions were adopted in 1881-1900. at the II-VII sessions of the International Geological Congress. Further, the World Geochronological Scale was constantly refined.
Periods were named according to various criteria. The most commonly used geographical names. So, the name of the Devonian period came from the county of Devonshire in England, the Jurassic - from the European Jura mountains, the Permian - from the city of Perm, and the Cambrian - from lat. Cambria, names of Wales.
Vendian, Silurian and Ordovician stages are named after ancient tribes. Names associated with the composition of the rocks were rarely used. The Carboniferous era is named so due to the huge number of coal seams, and the Cretaceous - because of the popularization of writing chalk.
Building basis
The geologic time scale was created to identify the conventional geognostic age of rocks. Absolute old agemeasured in years is of secondary importance to geologists.
The life of the Earth is divided into two main periods: the Cryptozoic (Precambrian) and the Phanerozoic, according to the appearance of archaic remains in sedimentary rocks. In the Cryptozoic, only soft-bodied organisms existed, leaving no traces in sedimentary rocks. This is the invisible life phase.
The Phanerozoic began at the moment when at the turn of the Cambrian and Ediacaran (Vendian) a mass of forms of mollusks and other organisms appeared, allowing paleontologists to divide the strata according to the finds of fossil fauna and flora.
The Earth's geological time scale has another major division, which is distinguished by the first attempts to split the history of our planet into the largest time intervals. Then the entire chronicle was divided into four periods: primary, equivalent to the Precambrian, secondary - Mesozoic and Paleozoic, tertiary - completely Cenozoic without the final Quaternary era. The Quaternary phase occupies a special position. This is the smallest cycle, a colossal number of events took place in it, the traces of which survived better than others.
Eons
The geologic time scale is an essential tool for every geographer. The Cryptozoic or Precambrian took place 4 billion - 542 million years ago. Oo differs in that the organisms did not have hard shells and skeletons. Their presence and history is almost impossible to detect, only by rare marks on the stones.
The time frame of the Phanerozoic is 542 million years ago to the present day. Determinedhard surface layers of organisms and skeletons, thanks to which the chronicle of the development of life can be traced with the help of fossils. Hidden life moved to explicit, apparently due to the fact that the atmosphere was saturated with oxygen. Then the ozone layer appeared, protecting the planet from radiation from space.
Such atmospheric changes were caused by the functioning of organisms. Perhaps this led to the extinction of many species for which oxygen was a poison.
Paleozoic era
So, we already know what the Phanerozoic geological time scale is. What is Paleozoic? This is ancient life that existed 542-251 million years ago, "before the dinosaurs." It is divided into the following periods:
- Cambrian phase: 542-488 million years ago. It's mostly marine life. The most common group of unicellular organisms are trilobites. However, the diversity of animals is such as it will never be again in history (one might say "Cambrian explosion").
- Ordovician time: 488-444 million years ago. Shellfish and corals are common. The first invertebrates appeared - jawless fish-like and terrestrial plants.
- Silurian stage: 444-416 million years ago. Arthropods and plants adapt to land, jawed fishes appear. The life of the oceans and seas is beginning to resemble the present.
- Devonian Gap: 416-359 million years ago. Insects, spiders and mites arose. Soil appears. Loop-finned and lungfish have adapted to life on land.
- Carbon,or Carboniferous phase: 359-299 Ma. It is determined by the impressive diversity of the flora of the land (in previous periods it was the same throughout the Earth). Giant arthropods and reptiles appear. Insects have mastered true flight. There are many swamps, as bacteria do not have time to utilize the dying vegetation. Sharks and other cartilaginous fish reign in the oceans and seas.
- Perm, or Permian era: 299-251 million years ago. The first archosaurs, the forefathers of dinosaurs, were born on Earth, and cynodonts with different teeth, the direct ancestors of mammals. Huge beast lizards appeared, like Dimetrodon, accumulating solar heat with the help of a "sail".
Mesozoic era
Even children know what the geologic time scale is. Grade 7, in accordance with the school curriculum, studies this issue. Students are aware that the Mesozoic is the era of dinosaurs that existed 251-65.5 million years ago. This phase is known for the following cycles:
- Triassic period: 251-200 million years ago. The variety of vertebrates has significantly decreased since the general extinction happened on Earth. Crocodiles, frogs, megasastrodons (true mammals), turtles and pterosaurs appear - the first vertebrates that can fly.
- Jurassic: 200-146 million years ago. Sea lizards dominate the water, dinosaurs dominate the land, and pterosaurs dominate the air. Jurassic mammals are quite small and resemble insectivores and rodents - just one niche that they have fallen after reptiles.
- Cretaceous time span: 146-65.5 million years ago. Most speciesdinosaurs reach their maximum size. Social insects, flowering plants, snakes, real birds, placental mammals appear.
Extinction
Who likes geography? The scale of geological time is one of the most important nuances of this subject. It is known that the Mesozoic and Cenozoic are separated by the most famous, but not the most numerous extinction in the history of our planet. At that time, all microfauna, including marine ones, disappeared. Experts have found a lot of evidence of the catastrophic events of that time, but their details and sequence are still being studied.
The base is the fall of a huge meteorite with a diameter of 11 km (more than Everest) in the Yucatan zone.
Cenozoic era
Cenozoic time frame: 65.5 million years ago – today. This cycle consists of the following periods:
- Paleogene phase (65.5 - 23 million years ago).
- Neogene cycle (23 million - 2,588,000 years ago).
- Anthropogenic (Quaternary) stage (2,588,000 years ago - today).
Neocene
The Neocene is a hypothetical geological epoch that will replace the Holocene in the future. Since the future has not yet arrived, there may be many options for his vision. However, experts can predict some phenomena based on the facts of the current change in the world: the direction and speed of movement of the continents, the approximatetilt of the Earth's axis, the course of ocean currents.
