Structure of the Earth
What is
the earth
like below
its
surface?
What
makes up
the interior
of our
planet?
Inside the
Earth 1:34
Compiled by
Susan Weidkamp
Chapter 22 Objectives
To observe how change is dependent on depth.
• The chemical makeup of the earth changes
as you go deeper.
• The density of materials increase with depth.
• Temperature and pressure increase with
depth.
To explain why these changes are observed.
To learn how models are used in science.
2
Earth has a few well kept secrets
3
Chemical vs.Physical
Chemical layers refer to the composition
or make up of the earth’s interior.
Physical Layers refer to the state of
matter such as solid, liquid , or in
between called “plastic.”
4
6. The
Moho
Boundary
Found
between the
chemical
layers of the
crust and the
mantle.
Andrija Mohorovicic (Mo-ho-ro-vi-chic)
discovered a boundary between the crust and
the mantle. The boundary is now known as the
“Moho,” or “Mohorovicic Discontinuity.”
5
7. Roughly,
how hot
is the Earth’s core?
6
Layers of the Interior of an Egg
Chemical Layers
of an egg:
Physical Layers of an egg:
Crust-solid
Crust-CaCO3
Egg whiteamino acids &
proteins
Egg whiteLiquid
Yolk- Liquid
Yolk- Lipids
Fatty acids
7
How do the chemical layers
change in an egg as you go deeper?
The type of compound changes from calcium
carbonate, CaCO3 to Proteins and the inner
yolk is mostly lipids or fat.
How do the physical layers
change in an egg as you go deeper?
The state changes from outer rigid solid to liquid egg white
and yolk.
8
Interior of the Earth
Compare the
physical layers on
right to the
chemical layers.
How are they
different? How
are they similar?
MOHO
9
8. How do the chemical layers change
in the Earth as you go deeper?
The type of material changes from compounds
like silicates to a core of mostly elemental and
metallic iron.
9. How do the physical layers change
in the Earth as you go deeper?
The state changes from the outer rigid crust a
solid, to the plastic asthenosphere to the
liquid core and the inner solid core.
10
Why are there more physical
layers than chemical layers?
10. Chemical layers:
Crust- Silicates of Al,
Fe and Mg
Mantle-Silicates of Fe
and Mg
Core- Metallic Iron
11. Physical layers:
Lithosphere –rigid
solid
Asthenosphere- plastic
Mesosphere- solid
Outer Core- Liquid
Inner Core- Solid
11
Scale of the Interior
12
How does the
temperature
change the
deeper you go?
The change in
temperature
and pressure
affect the state
of the interior
of the Earth
and density
probably has
the most effect
on the chemical
layers.
13
Check your neighbor
• How do the chemical layers change as
you go deeper?
• How do the physical layers change?
• Name the chemical layers:
• Name the physical layers:
14
How do we really know what the
center of the earth is like?
We have to make an educated
guess…
Or we go to the movies!
15
Ch. 22 Objectives Part 2
• How do scientists study the earth’s interior?
• Identify two types of seismic waves.
• Explain how scientists make inferences
about the earth’s core.
• Infer characteristics of an object through
indirect observation.
16
Indirect observations
Example #1 WIND
• When you do not actually observe the
wind, you see only its effects as the
branches of a tree move. The moving
branches are the indirect observation.
The wind is the inferred characteristic.
17
What is the core of the earth like?
A. Creamy Chocolate
B. Chewy Nougat
C. Soft Caramel
D. Hard “Rock”
Candy
18
What is the deepest hole in the earth?
12,345 meters or 7.67 miles
Sakhalin-1
19
Density Puzzle Inference #1
•Density of the earth equals
the earth’s mass divided by
its volume, or 5.5 g/cm3
Core must me more
to average 5.5 g/cm3
•Average rocks found in the
crust have a density of 3.5
g/cm3.
•What must be the core’s
density,
•more than 5.5 or
• less than 5.5?
20
Light energy waves bend
Light will bend and reflect at the
interfaces between different
materials.
Do seismic energy waves bend like
light?
Yes!
21
Seismic Waves
P waves are
PRIMARY WAVES
S waves are shear or
SECONDARY WAVES
They travel like a slinky.
They are the fastest, and are called:
They travel like a snake.
They are second fastest and are
called:
22
http://www.geo.mtu.edu/UPSeis/waves.html
23
Inference # 2 Earth’s
Interior has several
layers. Evidence:
P-waves bend at
every new layer.
S-waves
bend in solid
layers, but
stop at liquid
layers
24
The Moho
Boundary
Inference
#3
Between the
chemical
layers of the
crust and the
mantle.
Andrija Mohorovicic (Mo-ho-ro-vi-chic) discovered a
boundary between the crust and the mantle. He found seismic
waves speeded up at a depth between 30-35 km below the
surface. Why would they speed up?
A. The earth becomes hotter the deeper you go.
B. The earth becomes denser the deeper you go.
C. The pressure increases so particles are closer together.
The boundary is now known as the “Moho,” or “Mohorovicic Discontinuity.”25
http://www.infp.ro/Labs/file2.htm
Evidence from Seismic Waves
Recordings of
seismic waves
from earthquakes
gave scientists a
puzzle:
A shadow zone (no waves) appeared at 105
degrees.
26
Slower, Shear, S waves offer a clue
Transverse waves (S waves) as cannot travel through liquids.
Liquids have weak forces of attraction between the particles,
and these waves break up when they arrive. This explains why
there is a large “S” SHADOW ZONE.
27
Inference # 4
Evidence of the earth’s core
• Seismic waves bend as they pass
through interior; this creates a shadow
zone.
• The p shadow zone indicates the size of
the core.
• The s shadow zone indicates the
physical state of the outer core- liquid.
28
The Shadow Zone Puzzle
• The area beyond 105
degrees distance
forms a shadow zone.
At larger distances,
some P waves would
arrive, but still no S
waves.
• Only slow traveling
surface waves reach
this area traveling
through a thin layer
of crust.
Seismic waves bend at an interface, or chemical layer.
29
Inference #5
How big is the Earth’s core?
Using the 105 degree angle of the shadow
zone, and the Earth’s radius of about 6350km,
draw a a right triangle. Then calculate:
Radius of core
= cosine of 52.5 degrees
6350 km
Cosine of 52.5 = .60876
Core’s radius = 3870km
(52.5 degrees is half of 105 degrees,
and cosine = adjacent / hypotenuse)
30
31
IRIS video Clip
explaining shadow
zone
Turkey Part II
32
Propagation of Seismic Waves
33
34
How Earthquakes are located
35
Seismic Wave Analysis
The time between the two arrivals is exactly 10 seconds.
The ratio of velocities is 8.7 km/sec. The product of these
two values = 87 kilometers or the distance between the
seismometer and the earthquake.
36
Using a Time-Distance
Graph
37
Check your neighbor
• How did scientists discover the Earth’s
core?
• How are P waves different from S waves?
• What clue’s did the shadow zone tell us?
• About how big is the Earth’s core?
• Where is the “Moho” found?
Between the crust and the mantle
38
Physical Layers
Lithosphere - Lithos = “Rock, or stone”
Asthenosphere-Sthenos = “strong,”
asthenos = not strong ( prefix “a” negates)
39
The Lithosphere
Oceanic Crust- usually
found under oceans,
and near the edge of
continents.
Continental Crustusually found in
continents, forming
plains, and mountains.
40
Coast of the UK
41
Oceanic Crust
Oceanic crust
is mostly
made of dark
rocks like
basalt and
gabbro.
42
Continental Crust
Continental crust is less dense
than oceanic crust. It contains
more silicon, oxygen and
aluminum.
Most of the rocks are made of
granite and rhyolite.
43
What causes new crust to form?
What causes the volcanoes in the Pacific Rim?
44
Last Oregon Tsunami 1700
45
Movement in the Asthenosphere
How do temperature
changes affect the
movement of matter
in the mantle?
Hot matter rises, cools then sinks back.
46
Convection Cell
47
Convection Currents
Interior of
Earth
48
49
Plume rising through a
layered viscosity mantle
The plume
encounters a change
in viscosity.
It passes from the
lower mantle to the
upper mantle.
Now under less
pressure, it becomes
thinner (less viscous)
and faster.
50
Convection of Mantle animation
More Interactive animations
51
Viscosity
Changes in viscosity or thickness occur
due to changes in temperature. For
example hot maple syrup is less viscous
(thinner) than cold syrup. Question #23
52
Check your neighbor
• What makes up the lithosphere?
• What is the difference between oceanic crust
and continental crust?
• Describe the convection current within the
asthenosphere.
• How do changes in temperature affect the
viscosity of the mantle?
• What are the pros and cons of using computer
models to simulate the interior of the earth?
53
References
1.
2.
3.
4.
Earth Sciences Pictures. NASA Space Science Photo Gallery.
May 7, 2001.
http://pao.gsfc.nasa.gov/gsfc/earth/pictures/earthpic.htm
Louie, John N. Earth’s Interior.
http://www.seismo.unr.edu/ftp/pub/louie/class/100/interior.html
Seismic Waves. Alaska Earthquake Information Center.
Geophysical Institute. University of Alaska. May 7, 2001.
http://www.aeic.alaska.edu/Input/lahr/waves/waves.html
Investigating Earthquakes through Regional Seismicity.
Southern California Earthquake Center. May 7, 2001.
http://www.scecdc.scec.org:3128/Module/TableofC.html
54
References Continued
5.
6.
7.
8.
Camp Breakfast. Maple Grove Farms. May 7, 2001.
http://store.yahoo.com/maplegrove/campbreakfast.html
Some unanswered questions. USGS. May 7, 2001.
http://pubs.usgs.gov/publications/text/unanswered.html#anchor199283
10
Mantle Convection Subgroup. May 7, 2001.
http://wwwrses.anu.edu.au/gfd/Gfd_other_pages/Convection_demo/De
mo_page_2.html
Mantle, Plumes, Plate tectonics and Hot spots.May 7, 2001
http://icdp.gfz-potsdam.de/html/hawaii/objectives/plumes.html
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