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Geological Time scale

The organisms we see today come from a huge chain of evolution. When Earth first evolved, there was no favorable environment for the evolution of organisms on Earth. After continuous change in climatic condition, it became favorable to sustain life. During the course of evolution, many organisms evolved, developed and became extinct. The organisms which became extinct from the Earth left some evidences called fossils on sedimentary rocks. After complete study and analysis of these fossils, scientists discovered the process of evolution of life on Earth.

A brief history of the geological history and evolution of life is summarized in the given table. This description is based on  the book "The ICC's Geological Time Scale, 2012".

Geological history and evolution of life:-

Era: Precambrian

Duration: 4.5 billion years ago to 57 crore years ago

Major events:-

1. Igneous Rocks like gneiss and granite were formed in this era.

2. There was no existence of living beings before 3.8 billion years.

3. Bacteria evolved around 3.8 billion years ago and algae evolved around 3.2 billion years ago.

4.Evidences of existence of invertebrates during the end of this era is found.

5. Different types of changes over Earth's climate took place in this era.

Evolution of life:-

1. Origin of the Earth

2. Evolution of unicellular organisms and development of multicellular organisms.


Era: Palaeozoic 

Duration: 57 crore years ago to 25 crore years ago

Major events:-

1. Change in weather and atmosphere took place in this era.

2. Study of fossils of different plants and animals shows animals and plants developed from this era.

3. Sedimentary rocks were formed in this era.

4. Aquatic and terrestrial invertebrates and vertebrates were formed. For example: winged insects, fishes, amphibians.

5. Different types of green plants such as bryophytes and pteridophytes were formed.

Evolution of life:-

1. Development of a few marine organisms.

2. Development of vertebrates in Marine water.

3. Evolution of life on land, green vegetation and development of fishes.

4. Evolution and development of winged insects, fishes and plants.

5. Development of fern plants, evolution of amphibians and reptiles.

6. Extinction of many vertebrates and invertebrates and development of reptiles.



Duration: 25 crore years ago to  6 crore 50 lakh years ago

Main events:-

1.From the study of rocks in this era, it is found that different types of hills and mountains were formed in this era.

2. It was supposed that the vital conditions for the survival of lives on land, in water and in air were formed in this era.

3. A large number of reptiles such as huge dinosaurs and other reptiles were developed and highly abundant in this era and so this era is called "the age of reptiles". It is also called "the age of gymnosperms" due to higher abundancy of them in this era.

4. The origin, dominance and extinction of huge dinosaurs took place in this era.

Evolution of life:-

1. Evolution of dinosaur, reptiles and coniferous plants.

2. Dominance of reptiles, well developed dinosaurs, birds and other organisms.

3. Evolution of flowering plants and different insects, extinction of dinosaur and other large reptiles.


Era: Cenozoic

Duration: 6 crore 50 lakh years ago to present

Main events:-

1. Evolution of human beings took place in this era.

2. Breaking and expansion of rocks, volcanic eruptions, etc. took place in this era.

3. Ice was formed in this era. The climatic condition was changing with decreasing temperature. As a result mountain peaks were covered with ice.

4. Neanderthal man, toothed animals, gymnosperms and angiosperms evolved.

Evolution of life:-

1. Evolution of first mammal and horse.

2. Development of various mammals like elephant, Whale, etc. and development of owl.

3. Evolution of sharp-toothed cats and monkeys.

4. Development of grasses.

5. Evolution of human beings.

6. Development of stone age human beings and giant hairy elephants i.e. Mammoths.

7. Development of other mammals and dominance of human beings.