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The Earths’ Interior
Plate Tectonics
1
Earth Facts
Plate Tectonics
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Don’t copy this slide
Happy the man whose lot it is to know
the secrets of the earth. He hastens not
to work his fellows' hurt by unjust deeds,
but with rapt admiration contemplate
immortal Nature's ageless harmony,
and how and when her order came to be.
Such spirits have no place for thoughts of
shame.
- Euripides (484-406 B.C.)
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Inside the Earth
Plate Tectonics
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Crust
• The exterior
portion of the
earth
• Lies above
the Moho
discontinuity
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Crust
• 3 types of solid rock – igneous,
sedimentary, & metamorphic
• Oxygen & silicon
• Oceanic crust 8 km thick: basalt
• Continental crust 32km thick:
granite & basalt
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Don’t Copy
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Elements in the Crust
Oxygen
Silicon
Aluminum
Iron
Calcium
Sodium
Potassium
Magnesium
Titanium
Hydrogen
Plate Tectonics
46.6%
27.72%
8.13%
5.00%
3.63%
2.83%
2.59%
2.09%
0.40%
0.14%
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Mantle
• Layer between
the crust and
the core
• Silicon, oxygen,
iron &
magnesium
• 870°-2200°c
• 2900 km thick
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Lithosphere
• Thin outer shell of the
earth
• Consisting of the crust
and the rigid upper
mantle
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Lithosphere
• Rigid layer
• Broken up
into 7
major
lithospheric
plates
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Asthenosphere
• Zone of the mantle beneath
the lithosphere
• Consists of slowly flowing
solid rock
• Plasticity: when solid rock
flows
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Moho
• The Mohorovicic discontinuity
• Croatian scientist found
increased speed of seismic
waves
• Boundary between the
mantle and the earth’s crust
• Reveals increase in density
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Seismic
Waves
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Shadow Zones
• Location on the earth’s
surface where no seismic
waves or only P waves can
be detected.
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Core
• Central portion of earth
• Below the mantle
• Depth of about 2,900 kilometers
(1,800 miles)
• Consisting of iron and nickel
• Liquid outer core and a solid
inner core
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Magnetosphere
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Magnetosphere
• Region of space that is
affected by the Earth’s
magnetic field
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The Dynamic Earth
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Theory of Continental
Drift
• 1900’s Alfred
Wegener
proposed that the
earth used to be
one giant
landmass that
split to form
today’s
continents
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Continental Drift
• Pangaea
• Panthalassa
–“all lands”
–a single
landmass
–origin of all
the
continents
–“all seas”
–giant ocean
that must
have
surrounded
Pangaea.
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Wegener's Evidence for
Continental Drift
• The shape of continents
suggests they once fit
together
–Noticed first in 1858 as soon
as good maps were being
made
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Wegener's Evidence for
Continental Drift
• Fossils – The glossopterus
flora and fauna are now
found in widely separated
continents in the southern
Hemisphere.
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Fossil Evidence
• Fossils
support
Wegener’s
theory
•
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•
•
Glossopteris
Mesosaurus
Lystrosaurus
Cynognathus
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Wegener's Evidence for
Continental Drift
• Paleoclimate evidence
• Distribution of Paleozoic
–Coral reefs
–Coal beds
–Deserts
• 250-300 million years ago
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Wegener's Evidence for
Continental Drift
• Rock types and mountain
ranges can be traced across
now widely separated
continents.
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Rock Evidence
• Glacial
deposits
• Folded
mountains
• Coal
deposits
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Wegener's Evidence for
Continental Drift
• Evidence of ancient glaciers
in all of the southern
continents
• Do you think all of this
satisfied the critics?
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Where is the Force?
• What makes the plates
move?
• The answer is on the ocean
floor
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Mid-ocean Ridge
• System of undersea mountain
ranges
• Wind around the earth
• 65,000 km
• Ocean rocks much younger
than continental rocks
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Mid-Atlantic Ridge
• Undersea mountain range
• Steep, narrow valley down
the center
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Seafloor Spreading
• Movement of the ocean floor
away from either side of a
mid-ocean ridge
• Caused by convection
currents
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Seafloor Spreading
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Convection Cells
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Uneven heating causes
movement in fluids
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Paleomagnetism of
the Ocean Floor
• Magnetic fossil record of the
alternating magnetic field of
the ocean floor.
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Plate Tectonics
• Theory that the lithosphere is
made up of plates that float
on the asthenosphere
• Plates possibly moved by
convection currents
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Types of Crust
• Oceanic crust
–Material that makes up the
ocean floor
• Continental crust
–Material that makes up
landmasses
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Divergent Boundary
• Formed by two lithospheric
plates that are moving apart
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Rift Valley
• Steep, narrow valley
• Formed as lithospheric
plates separate
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Convergent Boundary
• Border formed by the
collision of two lithospheric
plates
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Continental vs.
Continental
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Oceanic vs Continental
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Subduction Zone
• Region where one
lithospheric plate moves
under another.
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Ocean Trench
• Formed when one oceanic
crust is subducted under
another oceanic crust
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Oceanic vs Oceanic
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Island arc
• Chain of volcanic islands
• Formed by subduction at
ocean trenches
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Transform Fault
Boundary
• Formed by two lithospheric
plates that slide past each
other
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Theory of Suspect
Terrains
• – theory that continents are a
patchwork of pieces of land
that have individual geologic
histories
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The earth was made so various,
that the mind of solitary man,
studious of change
and pleased with novelty,
might be indulged.
- Cowper, English poet
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Crust
• Asthenosphere
–Lithosphere
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Continental Drift
• Hypothesis stating that the
continents once formed a
single landmass
• Broke up and drifted to their
present location
Plate Tectonics
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The Earths’ Interior
Plate Tectonics
63
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