Earth's History
Science

The hypothesis that all the continents are moving very slowly across Earth’s surface
Continental drift
The hypothesis that all the continents are moving very slowly across Earths surface continental drift. Continental drift is the gradual movement of continents over Earth's surface due to tectonic plate motion.

A timeline of Earth's history based on major changes
Geologic time scale
A timeline of Earth's history based on major changes. Geologic time scale. The geologic time scale is a system that scientists use to organize Earth's history into different periods based on significant geological and biological events.

A fossil from an organism that existed for a short time, it is used to determine the age of other fossils
Index fossil
A fossil from an organism that existed for a short time, it is used to determine the age of other fossils. Index fossil. An index fossil helps scientists date rock layers and other fossils found in those layers.