The Geologic Time Scale (GTS) is a comprehensive framework that organizes Earth’s history into distinct intervals based on geological and biological events. It serves as a chronological timeline, enabling scientists to understand the age of rocks, fossils, and the evolution of life on Earth. The GTS is divided into several hierarchical levels, starting with the largest time intervals known as eons, which are further divided into eras, periods, epochs, and ages.
Within the Phanerozoic Eon, there are three eras: the Paleozoic Era (541 to 252 million years ago), marked by the development of marine and land life; the Mesozoic Era (252 to 66 million years ago), often called the Age of Reptiles; and the Cenozoic Era (66 million years ago to present), known as the Age of Mammals. Each era is further divided into periods, such as the Cambrian and Jurassic, which are characterized by significant geological and biological changes.