Earth: The
Water Planet
The Water Cycle
Water Cycle Notes
• The total
amount of
water on the
Earth remains
fairly
constant.
• The water
moves above,
across, and
through
Earth’s crust
and
ecosystems.
The Sun
• Heat energy from the sun drives
the water cycle.
• Heat reaches the Earth by
radiation.
Evaporation
• The process of liquid water
changing into water vapor.
• Oceans contribute about 80%
of all the water vapor in the
air.
Condensation
• The process in which water vapor changes
into liquid water as the water vapor rises
into the air and cools.
• When water vapor condenses on particles
in the air and tiny water droplets or ice
crystals form, a cloud is visible.
Precipitation
• Solid or liquid water that falls from the air to
•
•
•
Earth
Rain, snow, sleet, and hail are forms of
precipitation.
Form when drops of condensation in clouds
come together and grow too large to remain
suspended
Precipitation always “runs” downward due to
gravity
All precipitation starts as snow!
• Snow falls into warm air and melts = rain
• Snow falls into cold air and never melts on
the way down=snow
• Snow falls, melts, and refreezes as it
travels through cold air=sleet
• Snow falls, melts, refreezes and becomes
the “seed” kept suspended by updrafts
until it gets too heavy and falls=hail
“Lake Effect” Snow
•Cold , dry air blows over
large lakes and then over
land
Where does precipitation go?
• Most falls back into the ocean
• Some falls on the ground and soaks in
• Some falls on the ground and runs off the
surface into tributaries (streams and small
rivers that feed into a main river)
Transpiration
• The process by which plants release water
vapor into the air through their leaves
Groundwater
• Water located in the gaps and pores in
rocks below earth’s surface.
• Water gets there because the soil in
places is permeable which means water
can easily pass through.
• It can collect in large underground lakes
called aquifers.
• Wells can be dug to access groundwater.
Fresh Water
• Humans are 60%-75% water.
• Plants use water to make their own food.
• Both humans (animals) and plants need
fresh water.
• Fresh water has a very low salt content
• Only about 3% of all the water on Earth
is fresh water.
• Of that 3% over 2% is frozen.
Preserving Water Resources
• Since groundwater is our richest source of fresh
•
•
water, we must be careful with disposing of
chemicals.
Water treatment factories can filter and partially
purify water. (Boise WaterShed)
Wetlands act as natural water filters as
some waste settles out, is absorbed by plants,
and silt and mud are trapped by plant roots.