The Dynamic Earth

1
The Dynamic Earth
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What does dynamic mean?

• Ever changing in varying degrees of intensity.

3
The Sources of Energy for the Earth

• What is the source of the Earths dynamic nature?
• A constant flow of energy.
• External Sources of Energy
• Sunlight (Light Energy)
• Internal Sources of Energy
• Leftover thermal energy from the Earths
  formation
• Friction from the movement of the lithospheric
  plates
• Decay of radioactive elements (Uranium, for
  example)

4
The Earths Atmosphere

• Layers
• Composition
• Evolution

5
Atmospheric Layers

• Four Layers
• Thermosphere (outermost layer, receives intense
  solar radiation)
• Mesosphere (coldest layer)
• Stratosphere (contains the ozone layer, warmer
  due to absorption of ultra-violet light)
• Troposphere (the weather layer, the densest
  layer)
• Also, the Ionosphere (forms due to the
  interaction of cosmic radiation from the Sun with
  the faint nitrogen and oxygen concentration in
  the thermosphere)

6
Atmospheric Composition

• Nitrogen (N2) (78)
• Oxygen (O2) (almost 21)
• Argon (almost 1)
• Small amounts of other gases (0.1), including
• Water vapor
• Carbon Dioxide
• Methane
• Layer of Ozone (O3)

7
Atmospheric Evolution

• Primordial atmosphere contained mostly carbon
  dioxide and nitrogen, with some ammonia and
  hydrogenvolcanic gases.
• 2.5 billion years ago, a change occurred, plant
  cells algae, began to consume carbon dioxide and
  give off oxygen (photosynthesis)
• Atmosphere gradually filled with oxygen
• 350 million years agobasically same level of
  oxygen as today.

8
Earths Protection System

• Ultra-violet light shield (ozone layer)
• Thermal insulating blanket (greenhouse gases in
  the atmosphere)
• Solar wind blocker and atmospheric erosion
  protector (Earths magnetic field or
  magnetosphere)

9
Without the Ozone Layer

• Eventually, no terrestrial life (DNA destroyed)

10
Without the Greenhouse Gases

• Earth would much colder and iced over (-27
  degrees C)

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Without the Magnetic Field

• Atmosphere would be eroded by the solar wind, and
  cosmic radiation (electrons and protons from the
  Sun) would harm living organisms.

12
Greenhouse Effect

• The surface of the Earth is heated by visible
  light from the Sun. The Earth then radiates
  thermal energy as infrared light.
• The presence of greenhouse gases, CO2 and H2O and
  methane (CH4) and a few other trace gases, serve
  to trap or absorb some of the infrared light
  radiated from the Earths surface.
• Visible lights wavelength is too short to be
  absorbed by these greenhouse gases, but infrared
  lights wavelength is longer and can be absorbed.
• This interaction increases the surface
  temperature of the Earth.

13
Global Warming

• The greenhouse effect is a good thing for life.
  However
• Any increase in the greenhouse gas concentration
  (in parts per million) will cause more infrared
  light radiated from the Earths surface to be
  trapped, causing the Earth to become warmer.
• The recent increase in the concentration of
  carbon dioxide is due to the combustion of
  hydrocarbon- rich fossil fuels, such as coal,
  petroleum and natural gas. (cause see
  Industrial Revolution)

14
Ozone Layer

• Ozone absorbs the majority of incoming
  ultra-violet light from the Sun.
• Ozone is composed of three oxygen atoms, and is
  toxic to humans.
• Ozone holes or thinning is primarily caused by
  CFCs (chlorofluorocarbons)used in aerosol
  sprays, now banned worldwide.
• Some evidence of the healing of the ozone layer
  is observed, however, it is estimated that it
  should recover in another 2-3 decades without
  CFCs.

15
Earths Magnetic Field

• The source of the Earths magnetic field--The
  Dynamo Theory The rotation of the Earth causes
  the electrons in the outer liquid core (composed
  of molten iron and some nickel) to move. Moving
  electrons, as you recall, produce magnetic fields
  (that is, electromagnetism).

16
Atmosphere Pressure and Wind

• What causes the wind?
• Differences in atmospheric pressure.
• What causes differences in atmospheric pressure?
• Differences in the heating of the Earths
  surface.
• What causes differences in the heating of the
  Earths surface?
• Three reasons
• Angle of the sunlight striking the Earths
  surface
• Duration of the sunlight
• Ratio of sunlight being reflected vs. absorbed

17
Wind Belts and the Coriolis Effect

• Without the rotation of the Earth, two main
  convection cells would operate, from equator to
  poles.
• With the rotation, the winds are deflected either
  east or west, due to the Coriolis effect.
• Winds from the poles are deflected to the west,
  winds from the equator are deflected to the east.
• These are the prevailing winds (trade winds,
  westerlies and polar easterlies)

18
Ocean Currents

• Surface ocean currents circulate throughout the
  Earth.
• Surface ocean currents are produced by the
  prevailing wind belts.

19
Earths Thermal Energy Cycle

• Excess heat (thermal energy) accumulates in the
  vicinity of the Earths equator.
• This heats the atmosphere and the Earths oceans.
• Heat or thermal energy is moved away from the
  equator to the poles to equalize the temperature
  of the EarthEarth strikes a balance.

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Earths Thermal Energy Cycle

• How does the Earth correct for this imbalance in
  thermal energy (hot equator, cold poles)?
• Winds form a convection current from the equator
  to poles (warm air moves to the poles, is cooled
  and returns to be heated).
• Ocean currents carry warm water to the poles and,
  when cooled, the cooler water from the poles
  circulates to the equator to be heated again.

21
The Earth

• The layers of the Earth (Crust, Mantle and Core)
• Why layered?
• Differentiation (the settling of heavier
  elements, such as iron, towards the center of the
  Earth, less dense iron rich mantle rock floats
  on the dense iron core)
• Geochemistry (hot inner iron core under pressure
  can remain in solid state should also see a
  lowering of pressure away from center of Earth
  where solid iron core changes to liquid molten
  iron core)
• Geophysics (s-waves or transverse seismic waves
  cannot travel through liquids, and s-waves cannot
  penetrate the outer core thus, the outer core
  must be liquid)

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Fig. 1-10c, p. 14
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Differentiation
Fig. 1-10, p. 14
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Fig. 1-11, p. 15
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Fig. 9-21, p. 210
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Why does the surface of the Earth Constantly
Change?

• Water Cycle (weathering, erosion and transport of
  weathered rock sediments)
• Rock Cycle (melting of rock produces igneous
  rocks, weathering of igneous rock produces
  sedimentary rocks, and high pressure and
  temperature without melting produces a
  metamorphic rock.)
• Plate Tectonics (the Earths rigid
  lithospherecrust top part of the mantle is
  broken into plates that move into, away from or
  across each other)

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Fig. 1-15, p. 19
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What is Plate Tectonics?

• The rigid lithospheric plates move over the
  plastic flowing part of the mantle called the
  asthenosphere.
• As heat (thermal energy) from the core moves
  towards the Earths surface (heat flows from hot
  to cold), this produces convection currents in
  the mantle, which move the asthenosphere and drag
  the rigid lithospheric plates across the Earth.

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Fig. 1-3, p. 5
30
Plate Boundaries

• Divergent Plate Boundary (oceanic ridges and
  undersea volcanoessee the Atlantic Ocean)
• Submergent Plate Boundaries (trenches and
  volcanic mountain chainssee the Andes
  Mountains) also known as a convergent plate
  boundary.
• Transform plate boundaries (side-by-side plate
  motionsee the San Andreas Fault

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Fig. 1-13, p. 17
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The Mechanism for Plate Motion is Convection in
the Mantle
Fig. 1-12, p. 15
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Fig. 1-17, p. 20
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• Three types of plate boundaries
• Divergent plate boundary 2. Convergent Plate
  Boundary 3. Transform Plate boundary

Fig. 1-14, p. 18
35
Evidence for Plate Tectonics

• Geographic fit of continents
• Flora and fauna associations
• Paleomagnetism patterns associated with the iron
  in the spreading sea floor.
• Location pattern of volcanoes, earthquakes and
  mountains

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Fig. 2-4, p. 30
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Fig. 2-5, p. 31
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Fig. 2-6, p. 31
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Fig. 2-7, p. 32
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Fig. 2-8a, p. 34
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Fig. 2-8b, p. 34
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Fig. 2-10, p. 35
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Fig. 2-11, p. 36
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Who came up with this idea of Plate Tectonics?

• Alfred Wegener first suggested moving continents
  in his Continental Drift theory.
• But he had no mechanism he thought that perhaps
  the continents slowly plowed through the oceanic
  crust.
• Hess in 1960s began to observe age differences in
  sea floor core samples collected in the Atlantic
  Ocean. Youngest crustal rock was closest to the
  ridge and the oldest crustal rock was furthest
  away from the ridge (true for both sides of the
  ridge!)
• This became known as sea floor spreading.

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Fig. 2-3, p. 29
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Fig. 2-12, p. 36
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Fig. 2-13, p. 37
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Fig. 9-5, p. 191
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Fig. 2-14, p. 38
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Significance?

• Continental crust is less dense than oceanic
  crust, and literally floats in the oceanic crust.
• The lithospheric plate consists of continental
  and/or oceanic crust and the very top of the
  mantle.
• Continents are carried with the oceanic crust and
  top part of the mantle.
• This can lead to the formation of trenches,
  ridges, and mountain chains.

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Mt. Everest is still rising?

• Himalayan Mountains represent a subduction plate
  boundary, where an ocean separated two
  continents. As the ocean closed, the two
  continents collided, which produced the highest
  mountain chain in the world today, and is still
  pushing the continental crust upward.

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Fig. 2-15, p. 40
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Fig. 2-17, p. 42
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Fig. 2-18, p. 42
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Seismic Waves

• Seismic waves are produced by earthquakes when
  stresses build up by moving plates are suddenly
  released.
• Interior waves produced by this disturbance
  include longitudinal waves or p-waves and
  transverse waves or s-waves.
• P-waves are faster than s-waves, and can travel
  through solids or liquids. S-waves cannot travel
  through liquids.
• The epicenter and focus of an earthquake can be
  calculated using seismic data from at least three
  seismic stations.

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Fig. 9-21, p. 210
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Fig. 9-4, p. 191
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Fig. 9-8, p. 194
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Fig. 9-9, p. 195
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Fig. 9-10, p. 196
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Fig. 2-19, p. 43
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Fig. 2-23, p. 46