Chapter 2.1

Seventy percent of the earth’s surface is covered with water. There is water literally all around us in the form of water vapor, or water in the atmosphere in the form of gas.

The Water Cycle Did you know that the total amount of water on the earth’s surface does not change? Water constantly moves. Water goes from the oceans to the air to the ground and finally back to the oceans. This is the water cycle.

Evaporation The sun’s heat turns liquid water into water vapor, or humidity. Did you know that warm air can hold more humidity than cool air?

Condensation As water vapor rises and cools, it changes back into liquid in a process called condensation.

Precipitation Tiny droplets of water form clouds and fall back to the earth in the form of precipitation—rain, snow, sleet, or hail Precipitation soaks into the ground and collects in stream and rivers.

Collection During collection, streams and rivers carry the water back to the oceans. Then the cycle begins again.

The water cycle

Fresh Water Only about 2 percent of the water found on the earth is freshwater. Of that 2 percent, about 1.6 percent is frozen into giant sheets of ice, or glaciers. Groundwater fills tiny cracks and holes in the rock layers below the earth’s surface. There is 10 times more groundwater than there is water in rivers and lakes. Some of this water flows through underground rock layers called aquifers.

Salt Water The earth’s four major oceans—the Pacific, Atlantic, Indian, and Arctic Oceans—contain salt water, which is not fit for human consumption. Salt water is also found in seas, gulfs, bays, and straits.