GEOL 101

GEOL 101
Outline 13: Earth's Interior
What are the 4 major layers in Earth's interior? (crust, mantle, outer core, inner core)
What methods do we use to study the earth’s interior?
 mantle fragments (xenoliths) brought up in some volcanic eruptions
 meteorites: interpreted as pieces of planet – some basaltic, olivine-rich, metallic
 experiments: designed to duplicate pressure-temperature conditions inside earth
 seismic waves
3 basic principles of seismic waves:
(1) seismic waves travel faster through denser and more rigid materials
(2) S-waves cannot travel through liquids
(3) seismic waves may be bent (refracted) or reflected when they strike a boundary
Discontinuities – boundaries inside the Earth across which the velocities of seismic
waves change abruptly. Can be caused by:
(1) change in composition
(2) change in phases present (eg., melt vs solid).
Mantle (80% of Earth’s volume, upper portion composed of peridotite)
 What is the Moho?
 Low Velocity Zone = layer the plates “slide” on; also allows for isostatic
 asthenosphere
 Why is the low velocity zone there? (geothermal gradient crosses solidus line)
Outer Core (liquid Fe-Ni metal)
 What causes the S-wave and P-wave shadow zones?
 Magnetic field
Inner Core (solid Fe-Ni metal)
 How do we know that the inner core is solid?
How and when did the Earth become layered?
 What are the main sources of heat within the Earth?
Seismic tomography - What is seismic tomography and what does it show us?
Questions from Chapter 21 that we probably will not cover in lecture:
1. What is the difference between heat conduction and heat convection? (Question 5
on p. 504). Which process is more important in the mantle? In the crust?
2. How could seismic waves be used to detect a magma body beneath a volcano? In
other words, what features of the waves would indicate the presence of molten