Geologic Time Scale for Kids: Earth’s 4.6 Billion Year Story (Grades 6 to 8 Science)

Hi, I'm Luna from DoodleBeez. Earth is about four point six billion years old. That is hard to imagine! To make sense of it, scientists use a calendar of deep time called the geologic time scale.

The time scale splits Earth's history into chunks. The biggest are eons. Eons are split into eras, and eras are split into periods. Scientists mark the boundaries using rock layers and fossils.

The first four billion years are often called Precambrian time. That is almost ninety percent of Earth's history! For most of it, life was tiny and simple, like bacteria and algae.

The Paleozoic Era began about five hundred forty million years ago. Life exploded in the oceans. Fish appeared, then plants and animals moved onto land. It ended with a huge extinction.

The Mesozoic Era is the age of reptiles, when dinosaurs ruled. It ended about sixty six million years ago, when an asteroid struck Earth. We now live in the Cenozoic Era, the age of mammals.

Imagine all of Earth's history squeezed into one day. Dinosaurs would appear late in the evening. Modern humans would show up only in the last few seconds before midnight!

Now it's your turn. In which era did dinosaurs live, the Paleozoic, the Mesozoic or the Cenozoic? Pause and try. Dinosaurs lived in the Mesozoic Era, the age of reptiles.

Great job! Remember, the geologic time scale divides Earth's long history into eons, eras and periods, using rock layers and fossils. Practice the geologic time scale in the Science Lab at doodlebeez.com. See you next time!