Structure of the Earth

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: • 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