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