Dinosaurs existed about 250 million years ago to 65 million years ago. This era is broken up into three periods known as the Triassic, Jurassic, and Cretaceous periods. The Triassic Period lasted for 35 million years from 250-205 million years ago. Planet Earth was a very different place back then. All the continents were united to form one huge landmass known as Pangaea. The Jurassic Period was the second phase. The continents began shifting apart. The time scale for this famous period is from 205 to 138 million years ago. The CretaceousPeriod was the last period of the dinosaurs. It spanned a time from 138 million to about 65 million years ago. In this period the continents fully separated. However, Australia and Antarctica were still united. What is the central idea of the text?

Text Structure
Explain how the author developed the central idea