Geologic unit

A geologic unit is like a layer cake made out of rocks. Each layer contains different kinds of rocks and minerals that were formed over a very long time, like millions of years. Imagine if you were making a cake and you put different colored layers of batter on top of each other. The layers in a geologic unit are kind of like that, except they are made of rocks instead of cake batter. Geologists study these layers to learn more about the Earth's history and how it has changed over millions of years.