The hydrologic cycle describes the continuous movement of water on, above, and below the surface of the Earth. The three main stages are evaporation, transpiration, and precipitation. Evaporation and transpiration move water from oceans and plants into the atmosphere, where water vapor condenses and falls as precipitation. Precipitation provides the primary mechanism for delivering atmospheric water to the Earth's surface, where it runs off into streams and rivers or infiltrates into soils and groundwater. The hydrologic cycle is powered by energy from the sun and is crucial for sustaining life on Earth.

1. The hydrologic cycle The story of a drop in the proverbial “bucket”

4. Does the volume of the world’s oceans ever change? Last glacial period: Sea level 400 ft lower than today Last inter-glacial period: Sea level 18 ft higher than today 3M years B.P.: Sea level 165 ft higher

13. Global distribution of atmospheric water 100% -- 1,386,000,000 332,500,000 Total Global Water 2.5% 100% 35,030,000 8,404,000 Total Global Fresh Water 0.001% 0.04% 12,900 3,094 Atm % total water % total freshwater Volume (cu km) Volume (cu mi) Water Source

15. http://www. uwsp . edu /geo/faculty/ ritter /animation/atmosphere/precipitation_2001-2001_ nasa _EO_grid. mov

17. How many gallons of water fall when 1 inch of rain falls on 1 acre of land? About 27,154 gallons (102,800 liters) of water. On average, the 48 continental United States receives enough precipitation in one year to cover the land to a depth of 30 inches.