Class Notes:

A Layered Earth

 

 

A Layered Earth  (how do we know???)

 

 

 

 

Compositional Layers

1) Crust

a) Oceanic (~ 5 km)      

b) Continental (~ 40 km)

2) Mantle (~2900 km)

3) Core (~3500 km)

 

Mechanical layers

1) Lithosphere

2) Asthenosphere

3) Mesosphere

4) Outer Core

5) Inner Core

 

EarthÕs Compositional Layers

Layer

Volume

Density

Composition

Crust(cont.)

0.44 %

 

 

Crust (ocean)

0.16 %

 

 

Mantle

83%

 

 

Core

16.4 %

 

 

 

 

The Crust and Mantle are separated by the                                                            

 

 

 

 

 

 

N.B. The crust is not the same as the lithosphere!

 

 

Structure of the Crust and Upper Mantle

 

 

 

 

 

 

 

 

 

You shouldbe able to define and describe the characteristics of the following:

* Continentalcrust

* Oceaniccrust

* Moho

* Mantle

* Outercore

* Innercore

* Lithosphere

* Asthenosphere

 

 

How can we describe what we canÕt see? The earth as a black boxÉ

 

 

 

 

 

Velocity of Seismic Waves varies with rock properties, e.g.

 

Rock Elasticity: higher elasticity results in                           velocities

 

Rock Density: higher density results in                                velocities

 

 

 

Refraction and Reflection of a Beam of Light  

 

 

 

 

                                :the bending of wave rays caused by a change in velocity

 

 

Examples

 

 

Q. what is a wave ray?

 

 

A.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Q. What happens to a wave ray as it goes from a zone of low velocity to a zone of high velocity?

 

A.

 

 

Q. What happens to a wave ray as it goes from a zone of high velocity to a zone of low velocity?

 

A.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Q. What is the S-wave shadow zone and where does it occur?

 

A.

 

 

 

 

 

 

 

 

 

Q. What is forming the S-wave Shadow Zone?

 

A.

 

 

 

 

 

 

 

The S-wave shadow zone  

 

 

 

 

 

 

 

Q. We know where the core/mantle boundary is and that it is at least the outer part of the core is  liquid. What else do we know about the core?

 

 

 

 

 

Q. What is the P-wave Shadow Zone? (fig. 12.8)

 

A.

 

 

 

 

Q. What would a seismogram look like obtained at the following distances from an earthquake epicenter? (fig. 12.9)

 

1) 0-105o

 

 

 

2) 105o -140 o

 

 

 

3) 140o -180 o

 

 

 

 

Q. What can we say about the velocity of P-waves in the lower mantle and upper core, and how do we know?

 

A.

 

 

 

 

 

 

 

Changes in P-and S- wave velocity with depth (fig. 12.11)

 

 

 

 

 

Q. How did we discover the core?

 

 

A.

 

 

 

 

Q. What is the evidence for the Moho? (fig. 12.7)

 

 

 

 

 

 

 

 

 

 

Q. Why do mountains have roots?

 

 

 

 

 

Q. Why is it so hard to erode a mountain flat?

 

 

 

 

 

 

 

Q> What is the effect of adding and removing a continental ice sheet?

 

 

 

 

 

Estimated Geothermal Gradient (fig. 12.13

 

 

 

EarthÕs Internal Heat

 

1) Sources of Heat

 

a)                             

 

b)                            

 

2) Mechanisms of Heat Transfer

 

a)                             

 

b)                            

 

c) ?

 

                                :heat transfer by atomic or molecular impact.

 

 

                                :heat transfer by hot (less dense) material rising and cold (more dense)material sinking.

 

 

Mantle Convection as a Possible Mechanism for Plate Tectonics (fig. 12.14)