Download Basic Structure of the Earth - Choteau Schools-

Basic Structure of the Earth
How do we know what is inside the
Earth?
• Based on the speed and path of seismic
waves as they travel through the Earth.
– Speed/path of the waves are affected by
different densities.
• In general, density increases with depth.
• S waves cannot travel through liquid.
• http://www.pbs.org/wnet/savageearth/animations/in
dex.html
Layers (Inside – Out)
• Inner Core
– Large amount of pressure from above layers
cause the inner core to be solid and dense.
– Made mostly of iron with small amounts of
nickel, oxygen, silicon, and sulfur
Layers (Inside Out)
• Outer Core
– Liquid
• S waves cannot travel through this layer.
– Made mostly of iron
Layers (Inside – Out)
• Mantle
– Largest layer
– Made mostly of silicon, oxygen, magnesium,
and iron.
– Often divided into the upper and lower mantle
• based on changing speed of seismic waves
Layers (Inside – Out)
• Crust
– Varies from less than 5 km to more than 60
km thick.
– Contains more silicon and aluminum and less
magnesium and iron than the mantle.
Shadow Zone
• Area between 105 and 140 degrees from
the earthquake in which no seismic waves
are detected.
– Due to the bending of primary waves and the
stopping of secondary waves at the boundary
between the outer core and the mantle.
MOHO (Mohorovicic) Discontinuity
• Boundary between the crust and the upper
mantle (causes seismic waves to speed
up)