Transcript The Dynamic Earth - Fort Thomas Independent Schools

The Dynamic Earth
What does dynamic mean?
• Ever changing in varying degrees of
intensity.
The Sources of Energy for the
Earth
• What is the source of the Earth’s dynamic
nature?
• A constant flow of energy.
• External Sources of Energy
– Sunlight (Light Energy)
• Internal Sources of Energy
– Leftover thermal energy from the Earth’s formation
– Friction from the movement of the lithospheric plates
– Decay of radioactive elements (Uranium, for example)
The Earth’s Atmosphere
• Layers
• Composition
• Evolution
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)
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)
Atmospheric Evolution
• Primordial atmosphere contained mostly carbon
dioxide and nitrogen, with some ammonia and
hydrogen—volcanic 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 ago…basically same level of
oxygen as today.
Earth’s Protection System
• Ultra-violet light shield (ozone layer)
• Thermal insulating blanket (greenhouse
gases in the atmosphere)
• Solar wind blocker and atmospheric
erosion protector (Earth’s magnetic field or
magnetosphere)
Without the Ozone Layer
• Eventually, no terrestrial life (DNA
destroyed)
Without the Greenhouse Gases
• Earth would much colder and iced over
(-27 degrees C)
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.
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 Earth’s surface.
• Visible light’s wavelength is too short to be
absorbed by these greenhouse gases, but infrared
light’s wavelength is longer and can be absorbed.
• This interaction increases the surface temperature
of the Earth.
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 Earth’s
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)
Ozone Layer
• Ozone absorbs the majority of incoming ultraviolet 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.
Earth’s Magnetic Field
• The source of the Earth’s 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).
Atmosphere Pressure and Wind
• What causes the wind?
• Differences in atmospheric pressure.
• What causes differences in atmospheric
pressure?
• Differences in the heating of the Earth’s surface.
• What causes differences in the heating of the
Earth’s surface?
• Three reasons
– Angle of the sunlight striking the Earth’s surface
– Duration of the sunlight
– Ratio of sunlight being reflected vs. absorbed
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)
Ocean Currents
• Surface ocean currents circulate throughout
the Earth.
• Surface ocean currents are produced by the
prevailing wind belts.
Earth’s Thermal Energy Cycle
• Excess heat (thermal energy) accumulates
in the vicinity of the Earth’s equator.
• This heats the atmosphere and the Earth’s
oceans.
• Heat or thermal energy is moved away
from the equator to the poles to equalize
the temperature of the Earth—Earth strikes
a balance.
Earth’s 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.
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)
Fig. 1-10c, p. 14
Differentiation
Fig. 1-10, p. 14
Fig. 1-11, p. 15
Fig. 9-21, p. 210
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 Earth’s rigid lithosphere—
crust + top part of the mantle is broken into plates
that move into, away from or across each other)
Fig. 1-15, p. 19
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 Earth’s 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.
Fig. 1-3, p. 5
Plate Boundaries
• Divergent Plate Boundary (oceanic ridges and
undersea volcanoes—see the Atlantic Ocean)
• Submergent Plate Boundaries (trenches and
volcanic mountain chains—see the Andes
Mountains); also known as a convergent plate
boundary.
• Transform plate boundaries (side-by-side plate
motion—see the San Andreas Fault
Fig. 1-13, p. 17
The Mechanism for Plate Motion is Convection in the Mantle
Fig. 1-12, p. 15
Fig. 1-17, p. 20
Three types of plate boundaries
1.
Divergent plate boundary
2. Convergent Plate Boundary
3. Transform Plate boundary
Fig. 1-14, p. 18
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
Fig. 2-4, p. 30
Fig. 2-5, p. 31
Fig. 2-6, p. 31
Fig. 2-7, p. 32
Fig. 2-8a, p. 34
Fig. 2-8b, p. 34
Fig. 2-10, p. 35
Fig. 2-11, p. 36
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.
Fig. 2-3, p. 29
Fig. 2-12, p. 36
Fig. 2-13, p. 37
Fig. 9-5, p. 191
Fig. 2-14, p. 38
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.
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.
Fig. 2-15, p. 40
Fig. 2-17, p. 42
Fig. 2-18, p. 42
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.
Fig. 9-21, p. 210
Fig. 9-4, p. 191
Fig. 9-8, p. 194
Fig. 9-9, p. 195
Fig. 9-10, p. 196
Fig. 2-19, p. 43
Fig. 2-23, p. 46