Things were different on the land, too. Dinosaurs lived in forests and meadows instead of the animals like deer, buffalo and wolves which live there today.

Stegosaurus, the Colorado State Fossil

Phorusrhacos, a giant predatory fossil bird

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Knowing the ages of different fossils allows us to learn how life on earth has changed over long spans of time.

Different types of plants and animals lived at different times in the past. Scientists can examine certain chemicals in some rocks, called isotopes, to learn how long ago the rocks formed and how old the fossils in, or associated with, those rocks are.

broken jaw of fossil lizard Varanus rusingensis

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