1. Which of the following statements regarding what we know about Earth’s interior is most accurate?
We have been able to drill into the earth’s core
Much about what we know about Earth’s mantle and core comes from caves and mines
We know only about what is on the very surface of the earth, in what is known as the crust
Energy waves allow us to see precisely what is deep inside the Earth, like a “tricorder” or scanner from Star Trek

2. Earth’s Interior
What we know about Earth’s interior comes from indirect avenues of investigation.
Earth’s diameter is approximately 12,756 km (~ 7,500 miles).
-the deepest hole we have ever drilled into the Earth is only 9.6 km (~5 mi).
so how do we know what it’s like?
Seismic waves! - natural and man-made

3. some energy is absorbed as it encounters materials
Earthquakes
seismic (energy) waves travel through the earth
some energy bounces off harder layers
called reflection
some energy travels through but gets bent, changing the direction the wave is traveling
called refraction
some energy is absorbed as it encounters materials
called attenuation
Allow us to model what waves show up at given locations, and when they arrive at given locations.

4. Shallow high frequency seismic waves allow us to see reflectors and refractors at depth

5. Wave paths are influenced by density, temperature, and the angles at which they strike boundaries as they travel through and around the Earth

6. Factors affect seismic waves
distance: farther = more attenuation
density: higher = faster
temperature: colder = faster
liquid vs solid
- solid = faster; p-waves and s-waves
- liquid = slower; no s-waves
angle of incidence- controls how much is
reflected and how much is absorbed
vertical arrangement of layers
- controls the resultant direction of travel

7. P-wave and S-wave shadow zones
- caused by transmissive and refractive properties of the waves interacting with rock and liquid

8. Zones of material with distinctive characteristics make up each layer in the Earth
Greatly simplified it looks like concentric spheres

9. Crust- the rigid outer shell of the Earth, composed of solid rock; very thin- averages only 20 km thick (the crust is part of the Lithosphere)
two kinds of crust
Oceanic- most abundant; consists of rocks formed from mafic magma; very dense; very thin- 10 km thick
Continental- underlies continents; consists of rock formed from felsic and intermediate magma; less dense than oceanic crust; thick-30 to 85 km thick

10. What will happen as different kinds of crust interact with each other?
A) Oceanic and Continental - ?
B) Old Oceanic and Younger Oceanic - ?
C) Continental and continental - ?

11. Model of Lithosphere and Aesthenosphere showing thickness of Oceanic vs Continental crust
Oceanic crust
Continental crust
Uppermost mantle- Aesthenosphere
Mohorovicic Discontinuity
“The Moho”

12. Isopach contour lines = lines of equal thickness of the crust

13. The boundary zone between the crust and the mantle is called the Mohorovicic Discontinuity or the “Moho”
- a zone of low velocity transmission of seismic waves
Mantle- the semi-solid (jello-like) material underlying the crust. Extends down to about 3000 km depth
The uppermost part of the mantle is called the Aesthenosphere.
mostly molten material

14. The mantle is heated closer to the core
Heated mantle material rises upward very slowly
millions of years to move upward
As it near the earth’s surface, the mantle material liquefies
(due to pressure and temp relationships)
It also begins to cool, and slowly starts to sink back into the core
This creates a Convection current

15. Two highly schematic models of
mantle convection currents

16. 3D models of mantle convection currents
Heated rising material
Cooled sinking material

17. 3D maps of the earth’s convection currents based on seismic wave analysis-complicated looking!

18. Earth’s core Divided into an inner and outer zone
Outer zone is liquid- doesn’t transmit s-waves
Probably composed of Nickel (Ni) and Iron (Fe), some heavier radioactive elements, along with some other elements (S or N- Sulfur or Nitrogen)
Inner core is solid- based on speed of P-wave travel
composed of same materials as outer core
Important for generating Earth’s magnetic field

19. Earth’s magnetic field is created by the rotation of the outer fluid core around the solid inner core
This creates an
electrical current
Generates an
electromagnetic
Field.
Similar to a
bar magnet with
a positive and
negative end

20. Earth’s magnetic field fluctuates over time due to the unsteady nature of the geodynamo that is the the outer and inner core

21. Earth’s magnetic field interacts with solar particles, forcing them to the north or south pole, creating the Aurora Borealis