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Chapter 5
The Earth
Earth’s Vital Statistics
l  Mass=
6.0 x 1024 kg
l  Radius= 6378 km
l  Sidereal Period of Orbit= 365.26 days
l  Mean distance from Sun= 1.5 x 108 km
l  Average Density = 5.5 g/c3 (5520 kg/m3)
l  Surface = 71% water, 29% rock
l  Atmosphere mainly nitrogen and oxygen
More about Earth’s density
l  Average
Density = 5.5 g/cm3 (5520 kg/m3)
l  Density
of water ~ 1 g/cm3
l  Density of rock ~ 2 g/cm3 – 4 g/cm3
l  →
Interior must be much denser material
The six regions of Earth
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Inner core
Outer core
Mantle
Hydrosphere
Atmosphere
Magnetosphere
Earth’s Atmosphere
l 
1st atmosphere hydrogen and helium
Gravity not strong enough to retain
l  Heated by Sun and lost to space
l 
l 
2nd atmosphere from volcanic activity
Mostly carbon dioxide (CO2)
l  Most CO2 absorbed into oceans → limestone
l  Early plant life absorbed most of the rest CO2
l  Oxygen produced from early plant life
l  First formed minerals then built up in atmosphere
l 
Earth’s Atmosphere (cont.)
l  3rd
atmosphere is the present atmosphere
78% nitrogen, 21%oxygen, 0.9% argon, 0.03% CO2 …
Troposphere
l  Stratosphere
l  Mesosphere
l  Ionosphere (thermosphere)
l 
Atmospheric Components
l  Troposphere
l  ALL
Earth’s weather contained in this layer
l  Due
to convection
Atmospheric heating
l  Surface winds
l  Turbulence
l 
l  Extends
upward to 11 km above surface
l  Stratosphere
l  Extends
from 11km to 50 km above surface
l  The Ozone Layer begins in the stratosphere
Atmospheric Components
l  Mesosphere
l  Extends
from 50 km to 80 km above surface
l  The Ozone Layer extends into mesosphere
l  Ionosphere
l  Extends
(thermosphere)
higher than 80 km above surface
l  Layer that reflects radio waves back to Earth
l  100 km is the upper limit of the atmosphere as
accepted by the international community
The Ozone Layer
l  UV
radiation absorbed by ozone (O3)
l  UV radiation breaks down O3 → O2
l  Ozone layer shields the Earth from UV
l  Chloroflourocarbons (CFCs)
l  Carried
high in atmosphere by convection
l  Broken down by sunlight – release chlorine
l  Chlorine breaks down O3 → O2
l  1 chlorine atom can destroy up to 105 O3
Surface Heating
l 
Most of the radiation that reaches surface
Visible
l  Near-infrared
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l 
l 
Surface heats and reradiates following
blackbody curve
Wien’s Law → surface temperature of 250 K,
but surface temperature is ~ 290 K
Greenhouse Effect
Greenhouse gases (CO2, water vapor) trap infrared
radiation
l  CO2 have increased >20% over the last century
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Continuing to rise at ~ 4% per decade
Earth’s Interior
Earth’s Interior
l  Earth
originally molten
l  Heat
of accretion and radioactivity
l  Differentiation
created layers
l  Core
l  ~
80% iron
l  Radius ~ 3500 km total
l  Solid inner core radius ~ 1500 km
l  Mantle
l  Crust
l  Study
interior using seismology
Seismic Waves
l  Vibrations
that spread outward from the
site of an earthquake
l  Measured with seismograph
l  Provide information on Earth’s interior
l  Can
only drill to depth of ~ 10 km
l  (recall Earth’s radius ~ 6400 km)
Seismic Waves
l  P-waves
= primary waves
l  Pressure
waves (vibrate material)
l  Travel ~ 5-6 km/s
l  Travel through both liquids and solids
l  S-waves
l  Shear
= secondary waves
waves (side-to-side)
l  Travel ~ 3-4 km/s
l  Absorbed by liquid
Seismic Waves
l 
Speed of waves depend
on density of material
they pass through
l  Measure time of travel
l  Determine density of
material
Liquid outer core
(3500 km)
l  Solid inner core
(1500 km)
l 
Plate Tectonics
Plate Tectonics
l  Alfred
Wegener introduced idea of
“continental drift” in 1912
l  Seafloor spreading discovered as the
mechanism for continental drift
l  Continental drift led to modern theory of
plate tectonics
Plate Tectonics
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16 tectonic plates
Make up the lithosphere
l  Slide on the asthenosphere
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Plate boundaries
Convergent boundaries
l  Divergent boundaries
l  Transform fault
l 
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Subduction Zones
Earth’s Magnetic Field
l  Possibly
caused by differential rotation
l  Magnetic poles move – not aligned with
rotation poles
l  Magnetic field flips periodically
l  Magnetosphere surrounding Earth
l  Blocks
energetic particles (most from Sun)
l  Traps charged particles in Van Allen radiation
belts (causes aurorae – borealis/australis)
l  Occasional
CMEs make it through
Tides
l  Tides
result from tug-of-war between Earth
and Moon (and Sun)
l  Friction from the tides is causing Earth’s
rotation to slow, transferring angular
momentum to Moon
l  Moon
spiraling away at 3.8 cm per year
l  Will continue until Earth rotates at the same
rate as the Moon orbits the Earth
l  One “day” will = 47 days