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Earth: the home planet
Earth’s Interior
Earth’s Layered Structure
Earth’s interior consists of layers
 Layers are arranged according to density
 Most dense material is at the center – core
 Density decreases outward
 Density layering includes the hydrosphere
(oceans) and atmosphere
Thickness and Composition of
Earth’s Layers
Earth’s Temperature Structure
How Do We Know?
Refraction of Seismic Waves
Seismic Waves
Refraction – change in speed and direction
when passing through a material of different
Other Evidence
Refraction of seismic waves
 Density of the entire planet
 Gravity (mass) of entire planet
 Composition of meteorites
 Existence of magnetic field
Earth’s Magnetic Dynamo
Earth’s Magnetic Field
Was it always this way?
Accretion of the protoplanet
 Homogeneous structure
 Density differentiation
Density Differentiation
Gravitational effects vary with density of
 Materials must be free to move
 Requires plastic flow or fluid flow
 Requires heat
Earth: The Unfinished Planet
Earth continues to lose heat
 Volcanism brings material to Earth’s surface
 Other processes (subduction) return more
dense material to interior
 Conclusion:
Earth is still under construction!
Implications of an
Unfinished Planet
 Earthquakes
 Atmospheric and climate change
 Effects on life
Theory of Plate Tectonics
Earth’s lithosphere (crust +uppermost
mantle) is divided into plates
 Plates move as a result of heat inside the
 Plates interact to cause:
– Earthquakes
– Volcanos
– Mountain systems
What makes the plates move?
Uneven distribution of heat in the upper
mantle (Asthenosphere) causes heat to rise
in some places
 Differences in density cause colder, more
dense Lithosphere to sink back into the
 This Convection drives the motion of the
Interactions between Plates
 Volcanos
 Formation of mountains
 Formation of ocean basins
 Increase amount of continental lithosphere