Geological Time Scale

Table of Contents

The geologic time scale is a chronological dating system that classifies geological strata in time. This time scale is used by geologists, Paleontologists, and other Earth scientists to describe timing, relationships, and other events related to our planet in geologic history.

The geologic time scale is a calendar for events in Earth’s history.
An Eon is the largest period of geological time.
The subdivisions Eras are formed by the combination of periods, we can say eras are subdivided into periods.
Epochs combine together to form periods.
The epoch is the smallest unit of time scale.

Table: Geological Time Scale

The geological time scale depicting the evolution of life forms from unicellular bacteria to modern man is given below.

Era	Period	Epoch	Age	Life/major events
Cainozoic (From 65 million years ago to present time)	Quaternary	Holocene Pleistocene	0-10,000 10,000 – 2 Million	Modern Man Homo Sapiens
	Tertiary	Pliocene	2-5 Million	Early Human Ancestor
		Miocene	5-24 Million	Ape: Flowering Plants and Trees
		Oligocene	24-37 Million	Anthropoid Ape
		Eocene	37-58 Million	Rabbits and Hare
		Palaeocene	57-65 Million	Small Mammals: Rats-Mice
Mesozoic 65-245 Million Mammals	Cretaceous		65-144 Million	Extinction of Dinosaurs
	Jurassic		144-208 Million	Age of Dinosaurs
	Triassic		208-245 Million	Frog and turtles
Palaeozoic 245-570 Million	Permian		245-286 Million	Reptile dominate-replace amphibians
	Carboniferous		286-360 Million	First Reptiles: Vertebrates: Coal beds
	Devonian		360-408 Million	Amphibians
	Silurian		408-438 Million	The first trace of life on land: Plant
	Ordovician		438-505 Million	First Fish
	Cambrian		505-570 Million	No terrestrial life: Marine Invertebrate
Pre-Cambrian 570 Million -4,800 Million			570-2,500 Million	Soft-bodied arthropods
			2,500-3,800 Million	Blue-green algae: Unicellular bacteria
			3,800-4,800 Million	Oceans and Continents form-Ocean and Atmosphere are rich in Carbon dioxide
5,000 – 13,700 Million			5,000- Million 12,000 Million 13,700 Million	Origin of the universe Origin of the Sun stars Supernova, Big Bang

The image given below shows the geological time scale:

Geological Time Scale

Origin of Life

The last phase in the evolution of the earth relates to the origin and evolution of life. Modern scientists refer to the origin of life as a kind of chemical reaction, which first generated complex organic molecules and assembled them. This assemblage that they could duplicate themselves by converting inanimate matter into living substances.

The record of life that existed on this planet in different periods is found in rocks in the form of fossils.
The microscopic structures closely related to the present form of blue algae have been found in geological formations much older than some 3,000 million years.
It can be assumed that life began to evolve sometime 3,800 million years ago.

You can also read:

Thank you 🙂

Spread Your Love