Transcript The Water Cycle

The Water Cycle
Water never leaves the Earth.
All of it is constantly being cycled through the
atmosphere, ocean, and land. This process,
known as the water cycle is driven by energy
from the sun. The water cycle is crucial to the
existence of life on our planet.
During part of the water cycle, the sun heats
up liquid water and changes it to a gas by the
process of evaporation. Water that
evaporates from Earth’s oceans, lakes, rivers,
and moist soil rises up into the atmosphere.
The Water Cycle
Most evaporation takes place from the oceans
since there is more water there than anywhere
else on Earth.
Why is rainwater not salty, if most of it originated
from water evaporated from salty oceans?
First, let’s look at why the ocean’s are salty to begin with.
Ocean water is salty because it has minerals that wash
into the ocean from land and
dissolve. When weathering
creates sediment from rocks,
some of the minerals that
they were made from get
washed down rivers and into
the oceans.
Over billions of years the sodium chloride
(NaCl-salt) that was in the rocks on land
dissolved in the oceans and made them salty.
But when water evaporates from the ocean,
the salt stays behind. Remember when we
let the water evaporate from the beaker with
saltwater in it and the salt was left in the bottom?
Now, try to answer this question.
Tropical seas have a high rate of
evaporation. Because of this, the water in
tropical seas will have higher:
A. wave crests.
B. amounts of algae.
C. daily temperatures.
D. salt concentrations.
Now, let’s try another question.
There are many bodies of water in or
next to Georgia, including Lake Blackshear
and the Atlantic Ocean. What is MOST LIKELY
a difference between the water in
Lake Blackshear and the water in
the Atlantic Ocean?
A. The water in Lake Blackshear is
always much colder than the water in the
Atlantic Ocean.
B. The water in the Atlantic Ocean is part of
the water cycle, but the water in Lake
Blackshear is not.
C. The water in Lake Blackshear comes from
rivers, while the water in the Atlantic Ocean
comes from rain.
D. The water in the Atlantic Ocean contains
more dissolved minerals than the water in
Lake Blackshear.
In other words the water in the ocean is _______________ and lake water is not.
Here’s another question.
When ice forms in the oceans, what happens to the water
found directly underneath the newly formed ice?
Why don’t the oceans just keep getting saltier and saltier
as time goes by?
• The oceans are just as salty now as they were a million years ago and
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longer.
If you took a thousand pounds of seawater and could pull out all the salt,
you would have 35 pounds of salt. That’s measured as 35 parts per
thousand or 35 o/oo. (demo)
Even though the salt is left in the oceans when water is evaporated from
them, and weathering and erosion keep putting more salt in, the oceans
don’t get any saltier.
This is because about the same amount of freshwater flowing in from rivers
and falling as precipitation is almost exactly the same as the amount of
water that is evaporating from the oceans and about the same tonnage of
salt from the ocean water is deposited as sediment on the ocean bottom as
the amount of new salt coming in from weathering and erosion of rocks.
This is part of the balance created by the water cycle.
If not for this balance, the oceans would be so salty by now that most of
the marine life could not exist.
From where does the water evaporate that gives us our
rain in Columbus?
Transpiration (sometimes called evapotranspiration)
is similar to evaporation
The process of evaporation from plants is
called transpiration. (In other words, it’s like
plants sweating.)
Condensation is the step in the water cycle that takes place between
evaporation and precipitation.
As water (in the form of invisible gas) rises higher in the
atmosphere, it starts to cool and become a liquid again.
The water droplets then clump together around tiny dust
particles. This process is called condensation. When a
large amount of water vapor condenses, it results in the
formation of clouds.
Clouds are actually liquid water and dust particles that
aren’t heavy enough yet to fall back to Earth.
Precipitation returns the water in clouds back to Earth.
Remember, most precipitation over land comes from
water evaporated from the oceans.
When the water in the clouds gets too
heavy, gravity is the force that causes the
water to fall back to the earth. This is called
precipitation. Precipitation can take different
forms like rain, snow, sleet, or hail.
Runoff is rainwater that moves across the surface and
flows into lakes, rivers, streams, and the ocean
When rain falls on the land, some of the water is absorbed into the
ground forming pockets of water called groundwater. Soil is porous,
that is it has tiny spaces between the pieces of rock and other material
from which it is made. When a substance is porous and therefore
allows water to be absorbed it is said to be permeable.
Let’s list some other things besides soil that are permeable.
Most groundwater eventually returns to the ocean. Other precipitation
runs directly into streams or rivers. Water that collects in rivers,
streams, and oceans is called runoff.
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