Until the mid 1800s most people thought Earth was only a few thousand years old. Today there is much scientific evidence that some of Earth´s rocks are several billions of years old. Telling the relative age of rock layers is not as simple as these two ideas seem to be. Somtimes forces within Eath tilt , fold , or overturn layers of rocks.As people dig into rock layers, they often find fossils. Ossils are any remains , trace, or imprint of living thing preserved in Earth's crust. the era we live in now , the Cenozoic, began about 70 million years ago .
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