| A | B |
|---|
| Ice Age | Period during which low temperatures caused large areas of Earth's water to freeze. |
| Glacier | Thick sheets of ice that covered Earth's surface during the Ice Age. |
| Migrate | To move from one place to another. |
| Theory | One possible explanation for something. |
| Artifact | Object made by people in the past. |
| Archaeologist | Scientist who studies the artifacts of people who lived long ago and draws conclusions from them. |
| Ceremony | Activity done for a special purpose. |
| Mesa | High, flat landform that rises steeply from the land around it. |
| Drought | Long period without rain. |
| Civilization | Culture with organized systems of government, religion, and learning. |
| Surplus | More than is needed. |
| Specialize | Focus on one particular product, activity or job. |
| Pyramid | Building with three or more sides shaped like triangles that slant toward a point at the top. |
| Empire | Large group of lands and peoples ruled by one leader. |
| Tribute | Payment a ruler demands from people he or she rules. |
| Slavery | Practice of owning people and forcing them to work. |
