Geological time scale Upsc

Geological Time Division

It is the calendar of events of earth History. It is subdivided into eons, eras, periods, epochs and ages. It is used by Paleontologist, geologists to demonstrate the associations and timing of events.

Eons are the longest time division and ages is the shortest. The era we live in the Holocene epoch, Quaternary period, Cenozoic era and Phanerozoic eon.

90% of the earth’s history is made up of Precambrian time.

Geological time scale
By WoudloperDerivative work: Hardwigg – File:Geologic_clock.jpg, Public Domain,

Periods of Geological time scale

  • Precambrian (650 to 550 million years ago)
  • Cambrian (550 to 500 million years ago)
  • Ordovician (500 to 450 million years ago)
  • Silurian (450 to 400 million years ago)
  • Devonian (400 to 350 million years ago)
  • Carboniferous (350 to 300 million years ago)
  • Permian ( 300 to 250 million years ago)
  • Triassic (250 to 200 million years ago)
  • Jurassic (200 to 150 million years ago)
  • Cretaceous (150 to 100 million years ago)
  • Quaternary (50 million years ago to Present)

Geological Time scale with Events


It is the earliest geologic age. It is marked by different layers of sedimentary rocks that are laid over millions of years and these rocks contain a permanent record of the earth’s past such as fossils of plants and animals.


It is the first geological period of the Paleozoic era which is known as a time of ancient life. This period saw the burst of the incredible diversity of life that includes many animal groups that are present today.

One such are chordates from which vertebrates arrived.


This period is known for its diverse marine invertebrates that include graptolites, trilobites, etc. In this period, a rich variety of marine life flourished and the first primitive plants began to appear on land before the mass extinction ended this period.


The Silurian period was known for many biologically important events such as widespread radiation of crinoids in the oceans, expansion of brachiopods, a continued proliferation, and also oldest known coral reef found belonged to this age.

The animals that lived in this period are bryozoans, crinoids, clams, cephalopod, jelly, sea scorpion (Pterygotus), brachiopod, jawless fish (Birkenia), gastropod shell, brittle star, trilobite, bivalve mollusc, sponges, sea star, etc


The Devonian Period is known for the Age of fishes, as in this Geological time scale variety of fishes flourished. Some of the examples are armoured placoderms.

Other animals are the Earliest Arachnids, brachiopods, crinoids, other echinoderms, rugose coral, etc are common animals that flourished during this period.


It is characterized by dense and swampy forests that gave rise to huge deposits of peat. The peat is transformed into rich coal stores in Europe and North America.

The animals that lived during the Carboniferous Period are Primitive amphibians, reptiles, spiders, scorpions, etc.

The major during this period are shifting of continents due to which mountains are formed.


The Permian period is known for the greatest extinction of all time. The animals that lived during this time are Edaphosaurus, archosaurs, amphibians, fish, and invertebrates like insects, worms, etc.


The Triassic period is known for the time of great change. The period saw huge shifts in the diversity of life on Earth. The major event of this period might be a volcanic explosion, climate change, or being hit by a comet or asteroid that triggered the extinction of more than 90% of the earth’s species.


The Jurassic period is known as the fauna that transition from the Triassic fauna. It is dominated by both dinosauromorph and pseudosuchian archosaurs.

The first birds appeared during this period.


The Cretaceous is known for the animals now extincted such as marine reptiles, ammonites, rudist, and dinosaurs.

During this period new groups of mammals and birds appeared. Also, the flowering plants appeared.

The animals during this period are Ornithischians, iguanodon, Tyrannosaurus rex, etc


The Quaternary period is known for the glacial growth and extinction of many species and also the spread of humans.

It is ‘Age of Humans‘, Upright Man appeared in Africa during the starting of this period, and as the time evolved this creature went on become to rule the world.


Some of the major events in the geological time scale are the first appearance of life on earth, the formation of mountains, and the extinction of dinosaurs.

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* * All the Notes in this blog, are referred from Tamil Nadu State Board Books and Samacheer Kalvi Books. Kindly check with the original Tamil Nadu state board books and Ncert Books.
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