Structure of the Earth
Earth’s Compositional Layers
How do we know?
• Echo-sounding techniques are used to explore the Earth's crust. Images, similar to sonograms, are produced. A sonogram in the crust is called a seismic reflection. Seismic waves from "small explosions or thumper trucks" return echoes from rock layers. Seismographs pick up these echoes.
How do we know? continued
• Seismic measurements from earthquakes– P waves and S waves • P waves are primary waves, they travel faster than S
waves, which are secondary waves• P waves are compression waves, exerting a force
parallel to the direction of travel• P waves can travel through liquid or solid• S waves are shear waves that exert a force
perpendicular to the direction of travel• S waves can only travel through solid media
How do we know, continued
Crust
• 5 – 80 km thick• two types: – oceanic - thinner and more dense• 5 – 10 km thick
– Continental – thicker and less dense• 15 – 80 km thick
• Mostly made up of silicate rock• Comprises only 1% of Earth’s mass
Mohorovicic
• Boundary between crust and mantle
Mantle
• 2900 km thick• Iron• Comprises 66% of Earth’s mass
Core
• Radius of 3500 km• Iron and nickel• Comprises 33% of Earth’s mass
Structural Zones
• Lithosphere• Asthenosphere• Mesosphere• Outer core• Inner core
lithosphere
• 15 – 300 km thick• Comprised of crust and upper mantle• Brittle, cool portion of Earth• Outermost layer
Asthenosphere
• 200 – 250 km thick• Solid, but with ability to flow (plasticity)
Mesosphere
• Lower portion of mantle• Extends to 2900 km beneath surface• Solid rock
Outer core
• Extends to a depth of 5150 km beneath surface
• Dense liquid metal
Inner core
• Dense, rigid solid
Earth’s 4 “Spheres” of study
• Geosphere• Hydrosphere• Atmosphere• Biosphere
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