earth science

2. 1. Learn the origin of the waters in Earth’s oceans
2. Explain how dissolved salts and other substances get into
seawater
3. Describe the composition of seawater
4. Determine how surface currents are influenced by winds, the
Coriolis effect, and continents
5. Explain why waters off the western coasts of continents are
usually colder than waters off the eastern coasts of continents
6. Describe how density currents cause ocean water below the
surface to circulate
7. Describe the parts of a wave
8. Diff. between the movement of water particles in a wave and the
movement of wave energy
9. Describe how waves are created by the energy of wind and the
gravitational force of the moon and sun

3. Do this simple activity to discover how
currents work.
Fill a large beaker with warm water. You
could also use a pan of water instead of a beaker.
Gently add a drop of food coloring at the center.
Now carefully float an ice cube at the center. After
a minute, what happens to the food coloring? Add
two drops of food coloring directly on the ice cube
to help you see what is happening . You have just
made a density current.

4. The ocean is influencing you right now, no
matter where you live. If it is raining or snowing
today, most of that water came from the ocean. If
today is sunny, it is partly due to weather systems
that developed over the ocean. If you eat fish
today, it most likely will have come from the
ocean.

5. Oceans also affect the prices charged for
clothing, cars, and gasoline. The price includes the
cost of shipping those materials across a great
barrier, the ocean. If you live near a stream or river
that is polluted, that pollution eventually will
travel to the ocean. The ocean grately affect your
life.

6. • In the first billion years after Earth was
formed, its surface was much more
volcanically active than it is today.
• About 4 billion years ago, this water vapor
began to accumulate in Earth’s early
atmosphere. It eventually cooled enough to
condensed. Precipitation began to fall onto
Earth. Earth’s oceans were formed over
millions of years as this water filled low areas
on Earth called basins.

7. • Oceanographers have learned that the ocean
contains many dissolved elements, including
sodium, chlorine, silica, and calcium.
• Where do these elements come from?
One source is ground water, which very
slowly dissolves elements such as calcium
from rocks and minerals. The calcium is
then carried by rivers into the ocean.
Another source is the volcanoes that
erupt, releasing gases into the ocean.

8. • The two most abundant dissolved elements
are:
 Sodium – dissolved in river water that
flows into the ocean.
 Chlorine gas – added by volcanoes.
• When sodium and chlorine are combine in
the seawater, they form a salt called halite.
• Nearly 90% of the salt in seawater is made
of sodium and chlorine.

9. 96.50
%
3.2%
Ocean Water
Water
Salts
1.10%
1.20%
2.50%
3.70%
55.20%
30.50%
5.80%
Elements making
up salts in Ocean
Water
Potassium
Calcium
Sulfur
Magnesium
Chlorine
Sodium
Others

10. • Every 1,000 L of ocean water contains about
35 L of dissolved salts, or 3.5%.
• Salinity is a measure of the amount of solids
dissolved in seawater.
• The salinity of the ocean has stayed about the
same for hundreds of millions of years. This
tells us that the ocean’s composition is in
balance.

11. In some areas that have little fresh water, salt is
removed from ocean water. Saudi Arabia, which
borders the Red Sea and the Persian Gulf, for
example, makes fresh water from salt water using a
desalination system.
Desalting ocean water can be done in several
ways. In one method, salt water is boiled and the
steam is piped into a container where it cools. As the
steam forms, the salts are left behind and fresh water is
produced.

12. In another method, permeable membranes and
an electric current are used to separate the salt from
the water. Membranes that allow only negative ions to
pass. The electric current is then to further separate the
ions to produce fresh water.
In a third method of desalination, ocean water is
frozen. The salt crystals are separated from the ice
crystals by washing the salt from ice with fresh water.

13. 
• Surface ocean currents, just like surface
winds, are influenced by the Coriolis effect.
• Coriolis effect – the effect of Earth’s rotation
on the movement of air masses.
• The Coriolis effect causes most currents north
of the equator to move in a clockwise
direction. Most currents south of the equator
always move in a counterclockwise direction.

14. 
• Another factor that controls currents is the
continents that deflect currents. For
example, in the Pacific Ocean, currents
moving toward the west are deflected
northward by Asia and southward by
Australia, which deflect them toward the
equator.
• Surface currents are important because they
affect the climate of places they pass by.

16. 
• A density current occurs when denser seawater
moves toward an area of less dense seawater.
• Denser water around the North Pole and the
South Pole sinks and travels along the ocean floor
toward the equator. At the same time, less dense
water at the equator rises and moves toward the
poles along the surface. These two events form a
continuous cycle that circulates ocean water.

17. 
• What can make seawater denser and sink?
The cold air near the poles chills the
water, causing its molecules to be less active and
closer together. This decrease the volume of the
water and makes it denser, so it sinks. Also, the cold
climate freezes some of the water. This concentrates
the salts in the remaining unfrozen water, which
increases its mass, makes it denser, and causes it to
sink. Once this happens, the colder, saltier, denser
water moves as a mass along the ocean bottom.

19. 
• Waves are caused by winds, earthquakes, and the
gravitational fore of the moon and sun.
• Waves are movements in which water alternately
rises and falls.
• Parts of a wave:
 Crest – the highest point of the wave.
 Trough – the lowest point.
 Wave height – the vertical distance between crest and
trough.
 Wavelength – the horizontal distance between the
crests of two successive waves or the troughs of two
successive waves.

21. 
• Two different types of waves:
 the common sea waves caused by the wind
 the long waves of the tides.

22.  When wind blows across a body of
water, friction causes the water to be moved
along with the wind. If the speed is great
enough, the water begins to pile up, forming a
wave. As the wind continues to blow, the wave
increases in height.
 Waves stop forming when the wind stops
blowing. But, once set in motion, waves continue
moving for long distances. Waves you might see
at a seashore originated many kilometers away.
The height of waves depends on the speed of the
wind, the distance over which the wind
blows, and the length of time the wind blows.

23. 
• Tides - The periodic change in the surface
level of the oceans due to the gravitational
force of the sun and moon on Earth.
• Gravitational force is an attractive force that
exists between all objects. The strength of
gravity is affected by the masses of objects
and fall by a few meters twice a day. The tidal
range is the difference between the high tide
and low tide.

25. 
• The moon and Earth are relatively close together in
space, so the moon’s gravity exerts a strong pull on
Earth. The gravitational force of the moon is
stronger on the side of Earth that is facing the
moon. The moon’s gravity pulls in water particles
in the ocean and causes the water to bulge on the
side toward the moon and on the side opposite the
moon.
• These bulges of water on both sides of Earth are
waves that we call high tides when high tides
form, water is drawn away from the areas between
the bulges, creating low tides at those places.

26. • The sun also affects tides. The sun can
strengthen or weaken the moon’s effects.
When the moon, Earth, and sun are lined
up, high tides are higher and low tides are
lower than normal. These are called spring
tides. When the sun, Earth, moon form a right
angle, high tides are lower and low tides are
higher than normal. These are called neap
tides.