| A | B |
|---|
| Ice Age | period during which low temperatures caused large areas of Earth's water to freeze |
| migrate | to move from one area to another |
| artifact | object made by people in the past |
| ceremony | activity done for a special purpose |
| glacier | thick sheets of ice that covered Earth during the Ice Age |
| theory | one possible explanation for something |
| archaeologist | scientist who studies the artifacts of people who lived long ago and draws conclusions from them |
| mesa | high, flat landform that rises steeply from the land around it |
| drought | long period without rain |
| surplus | more than is needed |
| pyramid | building with three or more sides shaped like triangles that slant to a point at the top |
| tribute | payment a ruler demands from people he or she rules |
| civilization | culture with organized systems of government, religion, and learning |
| specialize | focus on one particular product, activity, or job |
| empire | large group of lands and peoples ruled by one leader |
| slavery | practice of owning people and forcing them to work |
