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: Mostly made up of silicate rock 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