What is the geological time scale based on?

The geological time scale refers to the arrangement of major and distinguishable events that have taken place in the geological past and also provides a glimpse of how the earth and the organisms have undergone significant evolution over a due course of time. It is based on the presence of fossils on the rocks of various sequences, and also the classification of rock types and the correlation of rocks of different locations.  It shows right from the time of formation of the earth, which is approximately 4.6 billion years ago.

This time scale is one of the main components of geology and is widely used by the paleontologists, geologists and other earth-related scientists, in order to construct the relation of various events that have occurred in the past.  

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