| A | B |
|---|
| air | a mixture of gases that surrounds the earth |
| cloud | a mixture of tiny particles of water, dust, and sometimes ice, floating in the air |
| groundwater | water that is stored in porous layers beneath the earth's surface |
| evaporation | process of liquid changing into gas |
| water cycle | way water circulates between air, the earth's surface, and underground aquifers |
| water vapor | state of water as an invisible gas |
| porous | having many small spaces or holes |
| aquifer | an underground layer of rock, sand, and soil where water is stored |
| gravity | the downward pull on all objects toward the center of the earth |
| condensation | the change of gas into liquid when the gas is cooled |
| percolation | water moving slowly down through the earth's layers |
