1. Structure of the Earth

2. Earth’s Compositional Layers

3. 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.

4. 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

5. How do we know, continued

6. 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

7. Mohorovicic
Boundary between crust and mantle

8. Mantle
2900 km thick
Iron
Comprises 66% of Earth’s mass

9. Core
Radius of 3500 km
Iron and nickel
Comprises 33% of Earth’s mass

10. Structural Zones Lithosphere Asthenosphere Mesosphere Outer core
Inner core

11. lithosphere 15 – 300 km thick Comprised of crust and upper mantle
Brittle, cool portion of Earth
Outermost layer

12. Asthenosphere 200 – 250 km thick
Solid, but with ability to flow (plasticity)

13. Mesosphere Lower portion of mantle Extends to 2900 km beneath surface
Solid rock

14. Outer core Extends to a depth of 5150 km beneath surface
Dense liquid metal

15. Inner core
Dense, rigid solid

16. Earth’s 4 “Spheres” of study
Geosphere
Hydrosphere
Atmosphere
Biosphere