Geologic Timeline

Geologic time is the way scientists describe the long history of Earth. Instead of using days or years, they use millions and billions of years to show how our planet has changed over time. The geologic time scale helps scientists organize Earth’s history into different sections, called eras and periods.

Earth is about 4.6 billion years old. Over this huge amount of time, the planet has gone through many changes. Scientists use fossils as clues to learn about what life was like long ago. A fossil is the remains or imprint of a plant or animal that lived a long time ago and became trapped in rock. For example, dinosaur bones and ancient leaves are fossils. By studying them, scientists can tell when certain animals lived and when they disappeared.

The geologic time scale is divided into major eras: the Paleozoic Era, the Mesozoic Era, and the Cenozoic Era. Each era is marked by big changes in life on Earth. For example, the Mesozoic Era is known as the Age of Dinosaurs, because dinosaurs were the main animals alive then. The Cenozoic Era is called the Age of Mammals, because mammals became more common after the dinosaurs went extinct.

Extinction happens when a type of plant or animal dies out completely. Mass extinctions, like the one that ended the dinosaurs, changed the course of life on Earth. These events help scientists divide time into different eras and periods.

Geologic time helps us understand how Earth’s surface, climate, and life have changed. For example, rocks and fossils found in the Grand Canyon tell us about ancient oceans and creatures that lived there millions of years ago. Learning about geologic time teaches us how slow and amazing Earth’s changes can be.

Interesting Fact: The oldest rocks on Earth are over 4 billion years old, almost as old as the planet itself!