The earth has a limited amount of water. That water keeps going around and around and around and around and (well, you get the idea)
This cycle is made up of a few main parts:

• evaporation_when the sun heats up water (rivers or lakes or the ocean) and turns it into vapor. The water vapor goes into the air.

• condensation _Water vapor in the air gets cold and changes back into liquid, forming clouds.

• precipitation_occurs when so much water has condensed that the air cannot hold it anymore. The clouds get heavy and water falls back to the earth. (as rain, hail, sleet or snow.)

Oxygen is what animals need in order to survive and carbon dioxide is what plants need for them to survive. Animals breath in oxygen and exhale carbon dioxide, while plants take in carbon dioxide and let out oxygen.

• animals need oxygen to compelete an internal cycle Resperation

• plants need carbon dioxide for Photosynthesis.