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The Structure of the Earth and
Plate Tectonics
Structure of the Earth
Mantle
• The Earth is
made up of 3
main layers:
Outer core
Inner core
– Core
– Mantle
– Crust
Crust
The Crust
• This is where we live!
• The Earth’s crust is made
of:
Continental Crust
Oceanic Crust
- thick (10-70km)
- buoyant (less dense
than oceanic crust)
- mostly old
- thin (~7 km)
- dense (sinks under
continental crust)
- young
How do we know what the
Earth is made of?
• Geophysical surveys: gravity, magnetics, electrical
etc
• Acquisition: land, air, sea and satellite
– Geological surveys: fieldwork, boreholes, mines
What is Plate Tectonics?
• If you look at a map of the world, you may notice that some of the
continents could fit together like pieces of a puzzle.
Pangaea
Continental Drift Theory
• Continental drift is the movement of
the Earth's continents relative to each
other by appearing to drift across the
ocean
• Developed by Alfred Wegener in 1912,
developed concept of Pangaea “oneearth”
Plate Tectonics
• The Earth’s crust is divided into 12 major
plates which are moved in various directions.
• This plate motion causes them to collide, pull
apart, or scrape against each other.
• Each type of interaction causes a
characteristic set of Earth structures or
“tectonic” features.
• The word, tectonic, refers to the deformation of
the crust as a consequence of plate
interaction.
World Plates
What are tectonic plates made of?
• Plates are
made of rigid
lithosphere.
The lithosphere is
made up of the
crust and the upper
part of the mantle.
What lies beneath the tectonic plates?
• Below the
lithosphere
(which makes
up the tectonic
plates) is the
asthenosphere.
Convection Currents
– The mantle is made of much denser,
thicker material, because of this the plates
"float" on it like oil floats on water.
– Caused by very hot material at the deepest
part of the mantle rising, then cooling,
sinking again and then heating, rising and
repeating the cycle over and over
Example
• The next time you heat anything like soup or
pudding in a pan you can watch the
convection currents move in the liquid. When
the convection currents flow in the mantle
they also move the crust. The crust gets a
free ride with these currents. A conveyor belt
in a factory moves boxes like the convection
currents in the mantle moves the plates of the
Earth.
Plate Movement
• “Plates” of lithosphere are moved around by
the underlying hot mantle convection cells
Sea Floor Spreading
• Magma comes up from the mantle in
the ocean
• Pushes previous crust that creates Mid
Ocean Ridges (mountain chains) on the
sea bed
• Magma creates new crust that spreads
out in its place
Sea Floor Spreading
Subduction of Crust
• Opposite of mid ocean ridges
• Earth’s crust is going into the mantle
and melts into the magma
• Continental crust and Oceanic Crust
collide creates subduction zone
• Ex. worlds oceanic trenches (deepest
part of earth’s surface)
Subduction of Crust