Download ES Ch2 Section 1 2005

Earth as a System
Chapter 2
1
Earth:
A Unique
Planet
Section 2.1
2
Objectives:
• Describe the size and shape of Earth.
• Describe the compositional and structural
layers of Earth’s interior.
• Identify the possible source of Earth’s
magnetic field.
• Summarize Newton’s law of gravitation.
3
Perfect sphere?
• Circumference
at poles is
40,007 km
• Circumference
at equator is
40,074 km
• oblate spheroid
• Rotation on axis
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Smooth?
• Relatively smooth
• Difference of only 20 km
compared to an average
diameter 12,735 km –
height of tallest mountain to
depth of deepest ocean trench
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The Hydrosphere
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• All the earth’s
water
• 71% of earth is
covered by water
– global ocean
• 97% of all water
is salt water
The Atmosphere
• A blanket of gases that
surround the earth
• 78% nitrogen
• 21% oxygen
• 1% includes other gases
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The Earth’s Interior
How do we know what the
earth’s interior is like?
Indirect Observations
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Film: Earth’s Interior
Tape #26
Earth Revealed
Time: 28 minutes
9
Zones of the Earth
Outer
•
10
http://www.seismo.unr.edu/ftp/pub/louie/class/100/earth-layers.GIF
Crust
• 1% of mass
• Oceanic crust - 5 to 10 km
thick
• Continental crust - 32 to 70
km
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•
http://metolab3.umd.edu/EARTHCAST/earth_jpl_sm
Mantle
12
• a very thick layer
reaching to
2,900km beneath
the crust.
• 1,000oC to
3,700oC
• 80% of volume
• 2/3 mass
• Plastic like
Dunite
• The only exposed sample of
the earth's mantle
•
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http://volcano.und.nodak.edu/vwdocs/Parks/hawaii/picture4.
gif
Mantle divided into 2 parts
• Lithosphere
• Solid portion
of the mantle
and the crust
• 65 - 100 km
thick
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• Asthenosphere
• Has the ability
to flow
• 200 km thick
• plasticity
–ability of a
solid to flow
Core
15
• the center of the earth
• 1/3 of earth mass
• made of Ni+Fe
• divided into two parts
Outer core
• 2,190km radius
• Liquid
Inner Core
 2680km diameter
 solid
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What’s inside the Earth?
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How do we know what the
interior of the earth is like?
Seismic Waves
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P waves or primary
waves
• travel through liquids and
solids quickly (6 km/s)
• compressional waves
19
S waves or secondary
waves
• travel through the solid crust
of the earth (3.5 km/s)
• shear waves
20
The Moho
• Boundary between the crust
and mantle 32 to 70 km deep
• Marked by the change in
speed of the wave
• Why?
• Mantle is denser
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Other changes - 100
km
• boundary between
lithosphere and
asthenosphere
• Seismic waves slow down
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2900 km
• boundary between Mantle
and Core
• P waves slow down-S waves
disappear
24
5150 km
• boundary between Outer and
Inner Core
• P waves increase in velocity
25
Shadow Zones
• Location where neither S waves
or P waves are detected.
26
•
http://www.seismo.unr.edu/ftp/pub/louie/class/100/earth-rays.GIF
Earth’s Magnetic Field
27
Magnetosphere
• Two magnetic poles – North
and South geomagnetic poles
• Lines of force extend between
each pole and beyond
atmosphere - magnetosphere
28
Magnetic source?
• Liquid iron in earth’s core
• Motions in outer core
produce electric currents
• Source may be like sun or
moon which are unlike earth
yet have magnetic fields
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Compasses
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Gravity
• Force of attraction between all
matter in the universe
• All objects are pulled towards
center of earth
• Force of gravity decreases as
distance from Earth’s center
increases
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Newton’s Law of
Gravitation
• The gravitational force
between two objects depends
on their:
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Mass
Large
Small
• direct proportion
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Distance
Large
Small
• inverse proportion
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Weight and Mass
• In the metric system, weight
(force) is measured in newtons
• a 1 kilogram mass has a weight of
about 10 newtons at sea level
• Weight – depends on mass and
distance from center of the earth
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Weight and Location
• Weight varies by location on
earth’s surface
• Distance between earth’s
surface and its center is
greater at equator than poles
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Assignments
• Section 2:1 Outline -Monday
• Section 2:1 Key Terms
• Section 2.1 Directed Reading
Worksheet
• Earths Interior
37