VOCABULARY Nº18

Superposition: the idea that in a series of rock layers the bottom layer is the oldest and the top is the youngest.








Relative age: the age of a rock compared with another rock.





Geologic column: a listing of Earth's rock layers in order from oldest to youngest.








Fossil: any trace, imprint, or remains of a living thing preserved in Earth's crust.








Index fossil: the remains of a living thing that was widespread but lived for only a short part of Earth's history.








Half-life: the time it takes for half the mass of an original element to change into a new product.





Absolute age: the age of a rock in year.





Era: one of the long stretches of time that Earth's history is divided into.