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The Structure of the Earth
Learning Objectives:
1. Describe the layers of the structure of the
Earth.
2. Describe the theory of continental drift.
3. Describe the theory of plate tectonics.
4. Explain how earthquakes and volcanoes
form.
Structure of the Earth
• Crust = thin, rocky
outer layer
• Mantle = properties
of solid but flows
slowly
• Outer core = liquid
nickel and iron
• Inner core = solid
liquid and iron
Continental Drift
• 1912 Alfred Wegner came up with the theory
of crustal movement or continental drift.
• Theory of Continental Drift = continents were
once joined together and gradually moved
apart
• Wegener’s ideas were not accepted at the
time.
Evidence Supporting Continental Drift
• Apparent fit of the continents = continents fit
like puzzle pieces
• Fossil Correlation = identical fossils have been
found on either side of the ocean
• Rock and Mountain correlation = identical
rocks and mountain structures have been
found on either side of the ocean
• Paleoclimate Data – coal found in cold regions
and glacial evidence found in warm regions
Plate Tectonics
• Theory of Plate Tectonics = the Earth’s crust is
broken up into pieces called tectonic plates
which float on top of the mantle
Convection Currents Cause Plates to Move
• Heat in the Earth
causes convection
currents in the
mantle.
• Convection currents
push the tectonics
plates which float on
the slowly moving
mantle.
Plate Boundaries = where plates meet
Plate Boundaries
Divergent Plate Boundary:
New Crust Formation
Continental Collision Boundary:
Mountain Ranges
Transform Boundaries:
Earthquakes
• Earthquakes can
occur at all
moving plate
boundaries.
• Plates do not
move smoothly
due to friction.
• Pressure builds
up and plates
“slip” suddenly
Subduction Zone Boundaries:
Volcanoes
• When one plate is
pushed under
another, oceanic
crust is pushed into
the Earth.
• Melting crust
releases gases
which can get
pushed upwards
creating a volcano.