What is a geological time scale ? Why is it created? You will find answers to these and other questions in the article. The geochronological scale (stratigraphic scale) is called the temporary geological scale of the 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
You do not know what a geochronological scale of geological time? 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 extreme old 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 with the lead-uranium method, the age of the CAI from the Allende meteor is 4568.5 Ma. Currently, this idea of the age of the solar system is considered the most accurate. The earth could have been formed much later than this - by several tens and even hundreds of millions of years.
The scale of geological time is quite an interesting thing. The subsequent period in the history of the Earth is divided into different time intervals. Their boundaries affect the most important events that have taken place.
The boundary between the times of the Phanerozoic appears through major evolutionary phenomena - global extinctions. The Paleozoic is separated from the Mesozoic by the largest Triassic Permian species extinction in the history of the Earth. Cenozoic and Mesozoic are separated by Cretaceous-Paleogene elimination.
Scale History
How was the geological time scale created? The nomenclature and hierarchy of most of the current geochronological units were adopted in 1881-1900. at the II-VII sessions of the Interethnic Geological Congress. Further, the World Geochronological Scale has been continuously updated.
The periods were named according to various signs. Most often used geographical names. So, the name of the Devonian period came from the county of Devonshire in England, the Jurassic from the European mountains of the Jura, the Perm from the city of Perm, and the Cambrian from Lat. Cambria, denominations of Wales.
The Vendian, Silurian and Ordovician stages are named after the ancient tribes. Names associated with the composition of the rocks were used very rarely. The Carboniferous era is named after a huge number of coal seams, and the Cretaceous due to the popularization of crayon.
The basis of the construction
The geological time scale was created to identify the conditional geognosic age of the rocks. Absolute old age, measured in years, is of secondary importance to geologists.
Earth's life is divided into two main periods: cryptose (Precambrian) and phanerozoic, according to the appearance of archaic remains in sedimentary rocks. In cryptozoic, there were only soft-bodied organisms that did not leave traces in sedimentary rocks. This is the phase of the invisible life.
The Phanerozoic began at the moment of the appearance at the boundary between the Cambrian and Ediacaria (Vendian) masses of forms of mollusks and other organisms, allowing paleontologists to separate 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 crush the history of our planet into the largest time intervals. Then the whole chronicle was divided into four periods: primary, equivalent to Precambrian, secondary - Mesozoic and Paleozoic, Tertiary - completely Cenozoic without a final Quaternary era. The quaternary phase has a special position. This is the smallest cycle, a huge number of events took place in it, the traces of which survived better than others.
Aeons
The geological time scale is a tool that every geographer needs. Cryptose or Precambrian took place 4 billion - 542 million years ago. GS differs in that the organisms did not have solid 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 - 542 million years ago and to this day. It is determined by the solid surface layers of organisms and skeletons, thanks to which the chronicle of the development of life can be traced using fossils. Hidden life passed to the obvious, apparently due to the fact that the atmosphere was saturated with oxygen. Next came the ozone layer, which protected 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 poison.
Palaeozoic
So, we already know what the Phanerozoic geological time scale is. And what is the Paleozoic? This is an ancient life that existed 542-251 million years ago, "before the dinosaurs." It is divided into the following periods:
- Cambrian phase: 542-488 Ma ago. It is mainly marine life. The most common group of unicellular are trilobites. However, the diversity of animals is such as it will never be in history (we can say the “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 the land, maxillary fish arise. The life of the oceans and seas begins to resemble the present.
- Devonian span: 416-359 million years ago. Insects, spiders and ticks arose. Soil appears. Pufferfish and double breathing fish adapted to life on land.
- Carbon, or Carboniferous phase: 359-299 Ma ago. It is determined by the impressive diversity of land flora (in previous periods it was the same throughout the Earth). Giant arthropods and reptiles appear. Insects mastered genuine flight. Many swamps, since bacteria do not have time to dispose of 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 the cynodonts of the Tooths are direct ancestors of mammals. Huge beastworms arose, like dimetrodon, which accumulates solar heat with the help of a “sail”.
Mesozoic era
Even children know what a scale of geological time is. Grade 7, in accordance with the school curriculum, is studying this issue. Students are aware that the Mesozoic is an 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 diversity of vertebrates has significantly decreased, since universal extinction has occurred on Earth. Crocodiles, frogs, megazastrodons (true mammals), turtles and pterosaurs appear - the first vertebrates that can fly.
- Jurassic period: 200-146 million years ago. Sea lizards dominate in water, dinosaurs on land, and pterosaurs in the air. Jurassic mammals are very small and resemble insectivores and rodents - just one niche that fell to them after reptiles.
- Cretaceous period of time: 146-65.5 million years ago. Most dinosaur species reach maximum sizes. Social insects, flowering plants, snakes, real birds, placental mammals appear.
Extinction
Who likes geography? The geological time scale is one of the most important nuances of this subject. It is known that the Mesozoic and Cenozoic are shared by the most famous, but not the most numerous extinction in the history of our planet. At that time, the entire microfauna, including the marine one, 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 fall of a huge meteorite with a diameter of 11 km (more than Everest) into the Yucatan zone is considered to be basic.
Cenozoic era
Cenozoic timeframe: 65.5 million years ago - today. This cycle consists of the following periods:
- Paleogene phase (65.5 - 23 Ma ago).
- Neogene cycle (23 million - 2,588,000 years ago).
- Anthropogenic (Quaternary) stage (2,588,000 years ago –– today).
Neocene
Neocene is called the geological hypothetical era, which in the future will come instead of the Holocene. 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 approximate inclination of the axis of the Earth, the course of ocean currents.