Seismic waves from earthquakes and explosions allow scientists to map the interior of Earth. Layers are identified by how fast p-waves and s-waves travel through materials with different densities and states. The crust is thin and varies in thickness and composition between continents and oceans. The mantle below is hot and convects slowly. The outer core is liquid and the inner core is solid, and their rotation generates Earth's magnetic field.

1. Which of the following statements regarding what
we know about Earth’s interior is most
accurate?
A) We have been able to drill into the earth’s core
B) Much about what we know about Earth’s mantle
and core comes from caves and mines
C) We know only about what is on the very surface
of the earth, in what is known as the crust
D) 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. 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. Uppermost mantle- Aesthenosphere
Continental crust
Oceanic crust
Mohorovicic Discontinuity
“The Moho”
Model of Lithosphere and Aesthenosphere showing
thickness of Oceanic vs Continental crust

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

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

22. Earth’s magnetic field plays a vital role in
the development of Plate tectonics theory
Identification of a process that
allows for Sea Floor Spreading.