Earth’s Interior
Essential Questions
• What are the layers of the Earth?
• What is the lithosphere, asthenosphere, and
mesosphere?
• What is an earthquake?
• What is the way to detect an earthquake?
• What are the ways to prepare for an
earthquake?
What are the layers of the Earth?
Bill Nye…..
• While watching the video complete your
movie worksheet. This is to be put into your
portfolio.
• http://learning.aliant.net/Player/ALC_Player.a
sp?ProgID=DEP_BN025
• 24mins
Layers of the Earth
Transition
region
Lower mantle
D“
Outer core
Inner core
Oceanic crust
Continental crust
Upper mantle
Layers of the Earth continued…
• Inner core:
– 1.7% of the Earth's mass
– depth of 5,150-6,370 kilometers
– unattached to the mantle, suspended in the molten
outer core
– is solid iron-nickel alloy
– is hotter than the outer core, may have a temperature up
to about 13,000°F (7,200°C = 7,500 K), but the intense
pressure keeps it solid
• Outer core:
–
–
–
–
30.8% of Earth's mass
depth of 2,890-5,150 kilometers
is composed of an iron-nickel alloy
is a hot, electrically conducting liquid
Layers of the Earth continued…
• D":
– 3% of Earth's mass
– depth of 2,700-2,890 kilometers
 Although it is often identified as part of the lower mantle, seismic
discontinuities suggest the D" layer might differ chemically from the
lower mantle lying above it.
• Lower mantle:
– 49.2% of Earth's mass
– depth of 650-2,890 kilometers
– is probably composed mainly of silicon, magnesium, and oxygen. It
probably also contains some iron, calcium, and aluminum.
• Transition region:
– 7.5% of Earth's mass
– depth of 400-650 kilometers
– is dense when cold because of the garnet. It is buoyant when hot
because these minerals melt easily to form basalt which can then rise
through the upper layers as magma.
Layers of the Earth continued…
• Upper mantle:
– 10.3% of Earth's mass
– depth of 10-400 kilometers
• Oceanic crust:
– 0.099% of Earth's mass
– depth of 0-10 kilometers
– the majority of the Earth's crust was made through volcanic activity.
• Continental crust:
– 0.374% of Earth's mass
– depth of 0-50 kilometers
– is the outer part of the Earth composed essentially of crystalline rocks.
Time to pause….
• In your portfolio answer the following
question:
– We often hear the Earth referred to as solid.
With the information you now have explain if
this is true or false.
What is the lithosphere,
asthenosphere, and mesosphere?
Earth’s Structural Zones
• The Earth is divided into 5 structural zones:
– Lithosphere
– Asthenosphere
– Mesosphere
– Outer Core
– Inner Core
• We have already reviewed the outer and inner
core.
Lithosphere
• It's very stiff, and fractures if you push too hard
• The lithosphere is part of the crust and the upper
mantle.
• The prefix "lithos" is Greek for "stone" or "rock."
• This layer is solid and the most rigid of the other
layers.
• It is about 15 to 300 kilometers thick.
Asthenosphere
• It's hot and flows like molasses
• The asthenosphere lies below the lithosphere.
• Its prefix "asthenes" is Greek for the word "weak.“
– Keep in mind; it is not as weak as a brittle piece of wood.
However, it is weaker than the other layers.
• This layer is about 200 kilometers thick
• It contains hotter, softer rock that flows like lava.
Mesosphere
• The mesosphere or "middle layer" is found at
the lower part of the mantle.
• Scientists believe it is solid rock.
So how do scientists know this?
• Geophysical surveys: seismic, gravity,
magnetics, electrical, geodesy
– Acquisition: land, air, sea and satellite
– Geological surveys: fieldwork, boreholes, mines
• What are seismic waves?
• When a sudden break or shift occurs in the earth's
crust, the energy radiates out as seismic waves.
• There are 2 categories of seismic waves:
– Body waves
– Surface waves
What is an earthquake?
Bill Nye - Earthquakes
• http://learning.aliant.net/Player/ALC_Player.a
sp?ProgID=DEP_BN027
• Complete the Question sheet provided.
• 24mins
Body waves
• Move through the inner part of the earth
• There are 2 types of body waves
– Primary waves, also called P waves or compressional waves
• P waves arrive first at any surface location
• can travel through solid, liquid and gas
• are waves that have the same direction of vibration along their direction
of travel, which means that the vibration of the medium (particle) is in the
same direction or opposite direction as the motion of the wave
• As they travel through rock, the waves move tiny rock particles back and
forth -- pushing them apart and then back together
• http://www.geo.mtu.edu/UPSeis/images/P-wave_animation.gif
– Secondary waves, also called S waves or shear waves
•
•
•
•
As these waves move, they displace rock particles outward
S waves don't move straight through the earth
only travel through solid material
the ground is displaced perpendicularly to the moves alternately to one
side and then the other
• http://www.geo.mtu.edu/UPSeis/images/S-wave_animation.gif
Surface Waves
• sometimes called long waves, or simply L wave
• are responsible for most of the damage associated
with earthquakes, because they cause the most
intense vibrations
• stem from body waves that reach the surface
• are something like the waves in a body of water -they move the surface of the earth up and down
• L waves are the slowest moving of all waves
P and S waves
• Both P and S waves refract or reflect at points where
layers of differing physical properties meet. They also
reduce speed when moving through hotter material.
These changes in direction and velocity are the
means of locating discontinuities.
• Seismic discontinuities (a surface at which velocities
of seismic waves change abruptly) aid in
distinguishing divisions of the Earth into inner core,
outer core, D", lower mantle, transition region,
upper mantle, and crust (oceanic and continental).
Earthquakes
• Did you know…
– According to the United States Geological Survey,
more than three million earthquakes occur every
year. That's about 8,000 a day, or one every 11
seconds!
What is the way to detect an
earthquake?
Detection
• Detecting an earthquake is much easier than
predicting one.
– a powerful earthquake can be felt by people in the area,
and the damage it causes can be seen.
• A machines, known as seismometers, or
seismographs, is used
– they can record the movements automatically,
– they work on a simple principle; that a heavy weight
suspended on a wire will remain steady as the vibrations
pass, whilst the frame holding it will be vibrated.
Reading a Seismogram
• When you look at a seismogram, there will be wiggly
lines all across it. These are all the seismic waves that
the seismograph has recorded.
• Most of these waves were so small that nobody felt
them.
Reading a Seismogram continued
• The P wave will be the first wiggle that is bigger than the rest
of the little ones (the microseisms).
– Because P waves are the fastest seismic waves, they will usually be the
first ones that your seismograph records.
• The next set of seismic waves on your seismogram will be the
S waves.
– These are usually bigger than the P waves.
– If there aren't any S waves marked on your seismogram, it probably
means the earthquake happened on the other side of the planet. S
waves can't travel through the liquid layers of the earth so these
waves never made it to your seismograph.
• The surface waves are the other, often larger, waves marked
on the seismogram.
– They have a lower frequency.
– Surface waves travel a little slower than S waves.
Finding the Epicenter
•
•
•
•
Measure the distance between the
first P wave and the first S wave. In this
case, the first P and S waves are 24
seconds apart.
Find the point for 24 seconds on the
left side of the chart below and mark
that point. According to the chart, this
earthquake's epicenter was 215
kilometers away.
Measure the amplitude of the
strongest wave. The amplitude is the
height (on paper) of the strongest
wave. On this seismogram, the
amplitude is 23 millimeters. Find 23
millimeters on the right side of the
chart and mark that point.
Place a ruler (or straight edge) on the
chart between the points you marked
for the distance to the epicenter and
the amplitude. The point where your
ruler crosses the middle line on the
chart marks the magnitude (strength)
of the earthquake. This earthquake
had a magnitude of 5.0.
The Richter Scale
• The Richter Scale is the best known scale for
measuring the magnitude of earthquakes.
• The energy released by an earthquake increases by
a factor of 30 for every unit increase in the Richter
scale.
• An earthquake that measures 4.0 on the Richter
scale is 10 times larger than one that measures 3.0
Richter scale no.
No. of earthquakes per
year
< 3.4
800 000
3.5 - 4.2
30 000
4.3 - 4.8
4 800
Most people notice them,
windows rattle.
1400
Everyone notices them,
dishes may break,
open doors swing.
4.9 - 5.4
Typical effects of this
magnitude
Detected only by
seismometers
Just about noticeable
indoors
500
Slight damage to
buildings, plaster
cracks, bricks fall.
100
Much damage to buildings:
chimneys fall, houses
move on foundations.
7.0 - 7.3
15
Serious damage: bridges
twist, walls fracture,
buildings may collapse.
7.4 - 7.9
4
5.5 - 6.1
6.2 6.9
> 8.0
One every 5 to 10 years
Great damage, most
buildings collapse.
Total damage, surface
waves seen, objects
thrown in the air.
What are the ways to prepare for an
earthquake?