How many eras divided in geological time?

Geological time periods are divided into Eons, Eras, Periods, and Epochs, sorted respectively in length.

Officially there are only three eras of geological time. Before the named eras is the Precambrian time period, which is only divided up into three eons; the Hadean (4.6 - 4 billion years ago), the Archean (4 - 2.5 billion years) , and the Proterozoic (2.5 billion to 545 million years ago).

For eras next is the Paleozoic Era, which ranges from 545 million years to 245 million years ago. The first fish and first land plants occured, as well as the first amphibians followed by the first reptiles. Right at the end the first dinosaurs evolved.

The next era is the Mesozoic, a short one. This was the dinosaur's era, for it contained the Triassic, the Jurassic, and the Cretaceous Periods. It was during the Triassic that Pangea first broke up. Towards the end of the Cretaceous Period, Most of the dinosaurs were extinct. It was in the Mesozoic Era that the first mammals appeared.

Finally we have the Cenozoic Era, which ranges from 66 million years ago to the present day. In this era most of the mountain ranges formed which we know today, and also the Ice Age occured.

epochs and periods {apex}