Earth’s Interior

Crust Outermost layer Cool Brittle – hard and easily broken Shallow earthquakes occur here Floats on the mantle 2 types of crust  Oceanic crust – lies under the oceans (5 kms thick)  Continental crust – forms continents (30 kms thick)

Mantle Between the crust and the core Thickest of all layers 3 parts  Upper mantle  Asthenosphere – just under the lithosphere and is the lower part of the upper mantle, soft, weak, more fluid than other areas  Lower mantle – largest part of all the mantle, great pressure causes rock to be rigid (not flexible), very hot but flows slowly

lithosphere Includes the crust and the upper mantle It is the plates that move about Earth’s surface

Core Center of the Earth Divided into two layers  Inner Core  Outer Core Made up of denser material than mantle Extremely HOT!!!

Inner vs. Outer Outer Core  Seismic S-waves show outer core is liquid  Mostly made of MELTED iron  As the outer core moves, electric currents are formed. Electric currents form magnetic currents. (EM waves)  Magnetic field protects Earth from Solar Radiation! Inner Core  Made mostly of SOLID iron  Pressure causes iron to be solid instead of melted

Sensing Earth’s Interior Seismic waves – vibrations that travel through Earth and are caused by events like earthquakes or human-made blasts Seismologist – a scientist who detects and interprets these vibrations using sensors at different places on Earth’s surface

Wave Motion Disturbance –a movement that begins in one location and sets things in motion farther away. Wave motion can be up and down or side to side

Two kinds of Seismic Waves P Waves Primary Waves Travel faster so they arrive first (primary) Move with a forward-and- backward motion (like a slinky) Can pass through solids and liquids and gases Move at different speeds depending on substance traveling through S Waves Secondary Waves Come after P waves Move with a side-to-side motion Can pass through solids but NOT liquids or gases Do not always record at all locations

What seismic waves tell us As P-waves and S-waves travel through Earth, they might be bent, reflected, sped up, slowed down, or stopped depending on the materials they go through. (Remember one of them cannot go through liquids or gases.) When an earthquake occurs on one side of the Earth S- waves are not detected on the other side of the Earth (because they cannot go through liquid). There must be liquid inside (magma in the asthenosphere)! The area that did not experience the S-waves is called the S-wave shadow zone.