The Water Cycle

1
The Water Cycle

• Chapter 11-1

2
The Water Cycle
3
Water on the Earth

• H2O
• Almost all the water on Earth is salt water
  (97).
• Of the three percent that is fresh water, 76 is
  frozen in the ice caps at the poles.

4
Groundwater

• Most of the fresh water that is not frozen is
  underground.
• The water that falls as precipitation sinks into
  the ground (permeable) and eventually reaches a
  layer it cannot pass through (impermeable).

5
The Water Cycle

• Continuous process by which water moves through
  the living and nonliving parts of the
  environment.
• The water cycle is driven by the sun.

6
Evaporation

• The process when the sun heats up the water in
  rivers, lakes, and oceans and turns it into vapor
  or steam. The water vapor goes into the
  atmosphere.
• Most of the water vapor that evaporates into the
  air comes from the oceans. The salt does not get
  enough energy to become a gas, so it stays
  behind.
• So rain is always fresh water!

7
Clouds

• Water vapor cools as it rises in the air. As it
  reaches the dew point, the water vapor will
  condense around dust particles and form clouds.

8
Precipitation

• Condensed water vapor that gets heavy enough to
  fall to the ground as rain, snow, sleet, or hail.
• Most water molecules only spend about ten days in
  the air before falling back as precipitation.

9
Surface Runoff

• Much of the precipitation runs off the surface
  and flows downhill into streams. These flow into
  larger streams, then rivers, and eventually flow
  back into the ocean.

10
Infiltration

• Infiltration is an important process where rain
  water soaks into the ground, through the soil and
  underlying rock layers.
• Some of this water ultimately returns to the
  surface at springs or in low spots downhill.

11
Groundwater

• Some of the water remains underground and is
  called groundwater.  As the water infiltrates
  through the soil and rock layers, many of the
  impurities in the water are filtered out. This
  filtering process helps clean the water.

12
Transpiration

• One final process is important in the water
  cycle. As plants absorb water from the soil, the
  water moves from the roots through the stems to
  the leaves.
• Once the water reaches the leaves, some of it
  evaporates from the leaves, adding to the amount
  of water vapor in the air.
• This process of evaporation through plant leaves
  is called transpiration. In large forests, an
  enormous amount of water will transpire through
  leaves. 
• The greatest living movers of water are plants.

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13
Earths Water Supply

• The total amount of water on the Earth has not
  changed much since early in its history.
• The same water is cycled over and over.
• The water you drink at lunch was probably drunk
  by a dinosaur millions of years ago!