Advanced Topics
In a nutshell: Earth's cycles, like the water and rock cycles, help renew and connect its systems.
## How Do Things Move in Cycles?
Many things on Earth move in repeating cycles that connect the four systems. Two important cycles are:
- **The Water Cycle**: Water evaporates from oceans, forms clouds, falls as rain, and flows back to the sea.
- **The Rock Cycle**: Rocks change from one type to another over time through heat, pressure, and erosion.
## Why Are Cycles Important?
Cycles keep Earth's systems balanced and healthy. Without them, plants wouldn't get water, and new soil wouldn't form.
## Real-World Connections
The water you drink today may have once been rain, a river, or even a cloud!
Examples
- Clouds forming from ocean water, then raining on mountains and flowing back to rivers.
- A volcano creating new rocks that eventually become soil through weathering.
Key terms
- Water Cycle
- The continuous movement of water on, above, and below the surface of Earth.
- Rock Cycle
- The process by which rocks are formed, broken down, and changed into new types.