Download Earth`s interior and tectonic plates notes

The Formation of the Earth
http://www.youtube.com/watch?v=_mcC8kFacrk
(formation of the earth video, 5 min)
• The effects of gravity
– as the planet reached a diameter of
about 350 km, the force of gravity
became greater than the strength of
rock.
– The center was crushed by gravity and
the planet started to become round.
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The Formation of the Earth
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• The effects of heat
– The collision of other objects generated
heat
– Radioactive material generated heat
– Soon the interior began to melt
How the Layers Formed
• As rocks melted, denser materials sank to the center of the
Earth and became the core.
– Nickel, iron
• Less dense material rose to the surface and became the
crust
– Oxygen, silicon, aluminum
• The middle layer is the mantle.
– Magnesium, iron
– http://www.youtube.com/watch?v=H6OuD877Rog
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• (formation of the Earth, 10 min)
Earth’s Interior
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ODE Standard: The composition and
properties of Earth’s interior are identified
by the behavior of seismic waves.
The Crust
• A layer of solid rock that includes both dry land and
the ocean floor.
– Very thin compared to the other layers, like the skin of an
apple.
– Thickest under high mountains, thinnest under the ocean
floor.
– 5-100 km thick
– Oceanic crust is denser than continental.
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The Mantle
• Made of very hot, solid rock.
– Lithosphere: uppermost part of mantle and the
crust together. Divided into tectonic plates.
– Asthenosphere: less rigid (plastic). Softer part
of the mantle, but still solid.
– Mesosphere: lower mantle made of solid
material that extends to the core.
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The Core
• Outer core: molten (liquid) metal. Movements
in this part of the core causes Earth’s magnetic
field.
• Inner core: dense ball of solid metal.
• Both are made of iron and nickel, but the
extreme pressure in the inner core keeps the
metal from becoming liquid.
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How do scientists know the
structure of the Earth?
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• Rock samples (direct evidence)
• Seismic waves (indirect evidence)
– Vibrations that travel through Earth
carrying energy released during an
earthquake.
– The speed and paths of waves reveal
the structure of the planet.
– We will learn more about these later.
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Tectonic Plates
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ODE Standard: Earth’s crust consists of
major and minor tectonic plates that
move relative to each other.
A Giant Jigsaw Puzzle
• The lithosphere is
made of plates
that fit together
like a puzzle.
• Vary in size and
thickness.
• Float on the
asthenosphere
like ice floats in
water.
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Wegener’s Continental Drift
Hypothesis
• Early 1900’s
• Continental drift continents once
formed a single
landmass, broke up,
and drifted to their
present locations.
• Pangaea existed
about 245 million
years ago.
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Sea Floor Spreading
• The process by which
new oceanic
lithosphere forms as
magma rises to the
surface and solidifies
• Evidence for
continental drift
• Mid-ocean ridges are
located where there is
sea floor spreading.
• Example: Mid-Atlantic
Ridge
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Tectonic Plate Boundaries
• Three types
– Convergent: plates
collide
– Divergent: where
plates separate
(mid-ocean ridges)
– Transform: plates
slide horizontally
past each other
(San Andreas Fault)
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Causes of Tectonic Plate
Motion
• Changes in density
within the athenosphere
• Energy comes from
center of Earth
• Heated rock expands
and rises (less dense)
• Cool rock contracts and
sinks (more dense)
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How is it measured?
• In centimeters per year
• GPS (global positioning
system) from satellites
– Scientists record the time
it takes for GPS ground
stations to move a given
distance
– This allows them to
measure the speed of the
plates motion
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Deforming the Earth’s Crust
• Deformation: the process by which the
shape of a rock changes because of
stress
• Stress: the amount of force per unit area
• Compression: stress caused by
squeezing. Convergent boundary.
• Tension: stress caused by stretching.
Divergent boundary.
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Folding
• Bending of rocks
because of stress
• Types
– Anticlines: upward
arching folds
– Synclines: downward,
trough-like folds
– Monocline: both ends
are horizontal
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Faulting
• The surface along which rocks break and slide
past each other
• Types
– Normal: usually with tension
– Reverse: usually with compression
– Strike-slip: opposing forces cause the rock to break
and move horizontally.
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Earthquakes
• Occur along faults
• Caused by stressed rock during plate
movement.
• Elastic rebound releases energy (remember
elastic potential energy?).
• This energy travels as seismic waves.
• These waves cause earthquakes.
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Earthquake Zones
• Along tectonic plate
boundaries where a
large number of
faults are located
• Example: San
Andreas Fault Zone
in California
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A Brief Introduction to waves
• Parts of a wave
–
–
–
–
Crest
Trough
Amplitude
wavelength
Waves Transfer Energy
• Transverse waves
– Particles vibrate perpendicular to the
motion of the wave.
• Longitudinal waves
– Particles vibrate parallel to the motion
of the wave.
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Behavior of Waves
• Diffraction
– Waves bend around an edge and spread
out. Ex. Sound waves
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• Refraction
– Waves bend as they pass from one medium
to another because the speed changes. Ex.
Straw in glass (light waves bending from air to
water)
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Behavior of Waves
• Reflection
– Waves hit an obstacle and bounce off. Ex.
Mirror
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• Absorption
– Waves enter into a material and lose energy.
Ex. Dark colored materials (blacktop)
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Behavior of Waves
• Constructive and Destructive
interference
– Waves come together to create bigger
or smaller waves.
Seismic Waves
• P waves: Pressure waves (or primary)
– Fastest, so they travel ahead of other waves
and are the first to be detected.
– Can travel through all media (solid, liquid,
gas).
– Move back and forth, which causes
compression and tension.
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Seismic Waves
• S Waves: Shear waves (or
secondary)
– Second-fastest waves
– Cannot travel through parts of Earth
that are completely liquid.
– Shear rock side to side as they travel
forward.
Seismic Waves
• Surface waves
– Move along the Earth’s surface (in the
upper few kilometers) of the earth’s
crust.
– Move the ground much like ocean
waves.
– Travel the slowest.
– The most destructive.
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• S and P waves give scientists a picture
of what is inside the Earth.
– P waves refract as they go from
one layer of the earth to another
– S waves diffract when they hit
something liquid
•
•
•
http://earthquake.usgs.gov/earthquakes/eqarchives/year/2002/
2002_11_03_waveani.php
http://earthquake.usgs.gov/learn/animations/animation.php?flas
h_title=Shadow+Zone&flash_file=shadowzone&flash_width=220&fl
ash_height=320
http://science.discovery.com/tv-shows/greatestdiscoveries/videos/100-greatest-discoveries-the-core-of-theearth.htm
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Earthquake Measurement
• Seismologist - a person who studies earthquakes
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• Seismographs - instruments that record seismic
waves
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• Seismogram - the “picture” that is created by the
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Determining Time and
Location
• Seismologists look at the seismogram to
note the difference in arrival times of P
waves and S waves
• Seismographs also help find the epicenter
and focus
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Measuring Strength and Intensity
• Charles Richter created the Richter scale
in the 1930’s.
• Measures the ground motion recorded by
seismograms at seismograph stations.
• Magnitude - a measure of the strength of
an earthquake
• Each unit on the Richter scale represents
motion that is 10 times larger than the
previous unit.
– A magnitude of 5 is ten times stronger than a
4.
– A magnitude of 6 is 100 times stronger than a
Modified Mercalli Intensity
Scale
• Intensity - a measure of the degree to
which an earthquake is felt by people
and the amount of damage caused
• Uses Roman numerals I to XII
• I = not felt, XII = total damage of an area
• The number changes depending on
where you are (highest number is close to
the epicenter).
Earthquake Forecasting
• Strength of earthquakes is related to
their frequency (how often they
occur)
• Scientists use this to help predict the
strength, location, and frequency of
future earthquakes
Earthquake Forecasting
• The Gap hypothesis
– Sections of active faults that have had
few earthquakes are likely to be sites of
strong earthquakes in the future.
– These sites are called seismic gaps
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Earthquakes and Buildings
• Retrofitting - making older buildings
more earthquake resistant
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– Fasten it to its foundation
– Technology that improves earthquake
resistance:
• Mass damper
• Active tendon system
• Base isolators
• Cross braces
• Flexible pipes
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Volcanoes
• Types of volcanoes
– Shield volcanoes
• layers of lava released from nonexplosive
eruptions.
• Ex. Hawaii’s Mauna Kea (the tallest
mountain on Earth)
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Types of Volcanoes
– Cinder cone volcanoes
• from moderately explosive eruptions.
• Ex. Paricutin in Mexico
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Types of Volcanoes
– Composite volcanoes
• most common
• From explosive eruptions.
• Ex. Japan’s Mount Fuji, Mount Rainier
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Other Volcanic Landforms
Caldera
Crater
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Lava plateau
Where Volcanoes Form
• Over plate boundaries
– Ex. Ring of Fire surrounding the Pacific
Ocean (contains 75% of active
volcanoes on land)
– 80% (on land) where plates collide
– 15% (on land) where plates separate
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Where Volcanoes Form
• Mid-Ocean Ridges
– Lava flows out to make crust
– Where most volcanic activity
takes place
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• Convergent boundaries
– During subduction, the
temperature and pressure
increase causing lava to form
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Where Volcanoes
Form
• Hot spots
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– Not along boundaries
– Above columns of rising
magma, results of cracks in
the crust
– Ex. Hawaiian Islands
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Predicting
Eruptions
• Dormant and Active (not
extinct)
• Monitoring earthquakes
• Studying volume and
composition of volcanic gases
(ratio of sulfur dioxide to
carbon dioxide)
• Measuring slope and
temperature
– GPS measures slope, infrared
satellite images show
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