Earth's Interior Introductory Geology GES 101 Dr. Bergslien

The Earth's Interior
Size of Earth:
Polar Radius = 6356.75km
Equatorial Radius = 6378.14km

Rotation about its spin axis causes the earth to be a very slightly flattened sphere

There are two basic ways of dividing the Earth into layers: Chemical Compostion and Physical Properties

Chemical Composition
Compositional Sorting - Overall Density Sorting of the Earth, Iron and Nickel sink to the center - lighter elements float upwards. Called the "Iron Catastrophe"

Chemical differentiation - chemical affinities of elements for each other. Uranuium has an affinity for oxygen, not iron, so it formed compounds that were relatively light and rose up rather than sinking to the core.

Compositional Layered structure:

Physical Properties - Mechanical Behavior

The layers are defined by their physical properties
With increasing depth, Earth's interior is characterized by gradual increases in temperature, pressure, and density

Depending on the temperature and depth, a particular Earth material may behave like a brittle solid, deform in a plasticÐlike manner, or melt and become liquid

Mechanical layers of Earth's interior are based on physical properties and hence mechanical strength

Mechanically Layered Structure

So - How do we know this ?

  1. Drilling Wells drilled into Earth are mostly in the upper 7 km of the crust. Deepest well is only a little under 8mi deep
  2. Volcanic activity Xenoliths = foreign rock (pieces of the mantle in lava). Only useful to depth of about 200 km
  3. High pressure laboratory experiments
  4. Samples of the solar system (meteorites)
  5. Study of seismic waves generated by earthquakes and nuclear explosions. Seismic waves are one of the main keys used to understand the EarthÕs Interior

Important Notes

Seismic Energy Wave energy gets reflected and refracted at seismic boundaries.