Physical Geography 102
Structure of the Earth


Formation of the Earth

Differentiation
Most dense material sinks to center.
Least dense material floats on top.

Looking into the Earth's Interior

Samples Surface samples
Drilling - 8-9 km deep
- deepest drill hole - 12 km
Ophiolite Sequences - 7-10 km deep
Xenoliths - 0-100 km deep
Kimberlites - 200 km deep

Looking into the Earth's Interior

How do we get information from deeper than 200 km?
Seismic Waves - Generated by earthqukes, reflect or refract off of materials in interior Reflection and refraction are affected by angle at which the wave strikes the material density of material physical state (solid or liquid) compostion of material.
Sources of seismic waves?

The Earth's Interior Least Dense to Most Dense

Atmosphere

- 0-500 km above surface

Oceans

- 0-11 km above solid surface

Crust

Contiental Crust & Oceanic Crust
Continental Crust
- average composition = granite
- density = 2.6-2.7 g/cc
- 10-70 km thick (average 33 km)
Oceanic Crust
- average composition = basalt
- density = 2.6-2.8 g/cc
- 6-10 km thick

Lithosphere

- contains the Crust and the Upper Mantle
- average composition = gabbro
- 100 km

Asthenosphere

- partially molten - 1-2 %
- capable of flow
- average composition = peridotite
-100-350 km

Crust - less dense
Mantle - more dense

Lithosphere - more rigid
Asthenosphere - less rigid

Upper Mantle

- partly solid - partly molten
- peridotite
- includes lowest portion of the Lithosphere and all of Asthenosphere
-~33-670 km

Lower Mantle

- average composition = peridotite*
* increased pressure has changed minerals
- 670-2900 km

Outer Core

- liquid iron and nickel
- 2900-5150 km

Inner Core

- solid iron and nickel
- 5150-6370 km

Earth's Magnetic Field

Magnetic Field is generated in the Outer Core.
Outer Core is liquid and convects due to heating from the Inner Core.
Convecting liquid iron acts as a large electric dynamo.
- generates a magnetic field.
Rotation of the planet also adds to this dynamo effect.