The age of the earth is around 4 - 5 billion years. We came from a long journey and we don't even know how exactly our earth came into the existence, but we made several theories, several hypothesis but the overall conclusion that we all agree is that once the earth was a ball of fire, lots of events took place, billion years have passed and so many things happened. Slowly the earth became colder, oceans formed, geological events happened lots of activities took place like rain, earthquake, volcanic eruptions.
Geologic Time Scale is a chronological parameter of events in the past which categories and classifieds them in a certain order that helps scientists, geologists to understand the history, extinction and the evolution of life on the earth.
In the year 1760 an Italian geologist Giovanni Arduino did the first classification of geological time his scale was based on his study of northern Italy, but for the world it was developed in Bologna city in International Geological Congress in 1881 and after that it has been gone through lots of improvements. Arthur Holmes who was a british geoscientist he made the first complete geological time scale in 1913.
When we studies about the history of the earth we need a geological time scale so we have different different classification of the geological time according to the events, species that we found studying the fossils, we divided this time in Era, Epoch and Periods.
1. Archean Era
2. Paleozoic Era
(i) Cambrian Period
(ii) Ordovician Period
(iii) Silurian Period
(iv) Devonian Period
(v) Carboniferous Period
(vi) Permian Period
3. Mesozoic EraThis era was 251.902 million years ago - 65 million years ago, and mesozoic era is also known as the Age of Reptiles and the Age of Conifers. This era can be classified into three periods.
(i) Triassic PeriodThis period was 251.902 million years ago - 201.3 million years ago, in this period the weather was arid which leads to the worse extinction event and majorly the life was destroyed which is known as the Great Dying. Mammals evolved in this period and the period is known as the age of reptiles, dinosaurs and crocodiles were particularly found.
(ii) Jurassic PeriodThis period was 201.3 million years ago - 145 million years ago, Brongniart named this period in 1829 after the jura mountains of alps. In the beginning of this Jurassic period the supercontinent Pangaea had started rifting into two landmasses Laurasia and Gondwana.
(iii) Cretaceous PeriodThis period was 145.5 million years ago - 66 million years ago, dinosaurs and lots of other creatures were extincted at the end of this period and after that the mammals got the opportunity to emerge.
4. Cenozoic EraThis era was 66 million years ago - 2.58 million years ago, in this era the temperature started decreasing and many parts were covered with snow which leads to the extinction of ancient creatures and new mammals and birds evolved in their place.
This era can be divided into five periods.