Ans: The blocks of time on the geological time scale are called eras
The history of evolution of life on earth is usually depicted in terms of geological time scale. The time scale has been divided by geologists and paleontologists into blocks referred to as 'era'. The 3 eras that have been currently identified are:
Paleozoic era which is the oldest and dates back nearly 540 million years
Mesozoic era which dates back to 250 million years ago
Cenozoic era which dates back nearly 65 million years
