How Do We Know How Old the Earth Is?

We can figure out how old the Earth is by looking at clues hidden inside rocks and using tools that work like a really slow timer.

Imagine you have a big jar full of jellybeans, and every year someone adds one jellybean to it. If you count how many jellybeans are in there now, you can guess how many years have passed, that’s like radioactive dating! Scientists look at special kinds of rocks called igneous rocks, which form when lava cools down. These rocks trap tiny bits of stuff that slowly change over time, just like the jellybeans.

Some of these bits are like magical jellybeans that turn into different flavors every certain number of years, scientists call this process radioactive decay. By counting how many of these "flavors" have changed, they can tell how long ago the rock was made.

They also look at layers of rocks, kind of like pages in a really thick book. Each page is a chapter, or a geological period, that tells a story about what happened on Earth back then.

By putting all these clues together, scientists have figured out that our Earth is about 4.5 billion years old, like it’s been reading stories for billions of years!