1. Earth’s Interior
Bob Leighty
GLG Physical Geology

2. These notes and web links are your primary “lecture” content in this class. Additionally, various articles are assigned each week to supplement this “lecture” information. I believe you’ll have enough information to reference without having to purchase a costly textbook.
These lecture notes are very similar to the ones I use in my traditional classes. You’ll find they are loaded with imagery and streamlined text that highlight the most essential terms and concepts. The notes provide a framework for learning and, by themselves, are not meant to be a comprehensive source of information.
To take advantage of the global knowledge base known as the Internet, I have included numerous hyperlinks to external web sites (like the Wikipedia, USGS, NASA, etc.). Follow the links and scan them for relevant info. The information from linked web sites is meant to supplement and reinforce the lecture notes – you won’t be responsible for knowing everything contained in them.
As a distance learning student, you need to explore and understand the content more independently than in a traditional class. As always, I will help guide you through this learning adventure. Remember, Dr. Bob if you have any questions about today’s lecture
Leave no questions behind!
Explore and have fun!

3. How We Know What’s Inside Earth
Earth’s Interior
Seismology – Seismic waves provide a detailed look at Earth's interior
Theoretical modeling
Petrology – Field & lab studies
Gravity & magnetic studies

4. How We Know What’s Inside Earth
Earth’s Interior
Earth’s Interior
How We Know What’s Inside Earth
WWW
Seismic Waves
Wave velocity increases with depth
Wave paths are interrupted by certain layers (discontinuitues)

5. How We Know What’s Inside Earth
Earth’s Interior
How We Know What’s Inside Earth
Seismic Waves
These layers have been mapped by seismic reflection (bouncing) & refraction (bending)

6. How We Know What’s Inside Earth
Earth’s Interior
How We Know What’s Inside Earth
Seismic Waves
Seismic tomography uses seismic waves to describe Earth's interior in 3D
> Slow areas (hot) - near volcanic areas, mid-ocean ridges
> Fast areas (cold) - subduction zones, continental interiors

7. How We Know What’s Inside Earth
Earth’s Interior
WWW
Gravity
Matter produces a gravity field in all directions
Inverse-square forces decrease rapidly with distance
> Stronger gravity = Closer and/or more massive
> Weaker gravity = Farther and/or less massive

8. How We Know What’s Inside Earth density = mass (g) / volume (cm3)
Earth’s Interior
Gravity
More mass = stronger gravity
> Higher density rocks = stronger pull
> Lower density rocks = weaker pull
density = mass (g) / volume (cm3)

9. How We Know What’s Inside Earth
Earth’s Interior
Gravity
Variations in Earth’s gravity field = anomalies
> stronger gravity   (+) anomaly
> ore deposits, mafic rocks   (+) anomalies

10. How We Know What’s Inside Earth
Earth’s Interior
Gravity
Variations in Earth’s gravity field = anomalies
> weaker gravity   (-) anomaly
> salt, felsic rocks, basins, craters   (-) anomalies

11. How We Know What’s Inside Earth
Earth’s Interior
WWW
Magnetism
Earth has a magnetic field much like a bar magnet
Earth’s magnetic poles are NOT the same as its geographic (rotational) poles

12. How We Know What’s Inside Earth
Earth’s Interior
How We Know What’s Inside Earth
Magnetism
Magnetic polarity = direction of magnetic field lines
Polarity changes - either “normal” (now) or “reverse”

13. How We Know What’s Inside Earth
Earth’s Interior
How We Know What’s Inside Earth
Magnetism
Magnetic polarity = direction of magnetic field lines
Polarity changes - either “normal” (now) or “reverse”

14. WWW How We Know What’s Inside Earth
Earth’s Interior
WWW
Paleomagnetism (ancient magnetic fields)

15. How We Know What’s Inside Earth
Earth’s Interior
Paleomagnetism (ancient magnetic fields)
Example: Mid-Ocean Ridges
Time 1 = Normal polarity
Time 2 = Reverse polarity
Time 3 = Normal polarity

16. How We Know What’s Inside Earth
Earth’s Interior
How We Know What’s Inside Earth
Magnetism
Magnetic anomalies are useful in finding buried magnetic objects
> more magnetic   (+) anomaly
> ore deposits, mafic rocks   (+) anomalies

17. How We Know What’s Inside Earth
Earth’s Interior
Magnetism
Magnetic anomalies are useful in finding buried magnetic objects
> less magnetic   (-) anomaly
> basins, craters, salt domes   (-) anomalies

18. Earth’s Interior
Earth’s Interior
WWW
Solid Fe-rich Inner Core, liquid Fe-rich Outer Core, and a silicate-rich mantle & crust

19. Earth’s Interior Lithosphere Crust + rigid upper mantle = LITHOSPHERE
The lithosphere is broken into numerous plates (tectonic plates)
Lithospheric plates slowly move over a weaker mantle layer (ASTHENOSPHERE)

20. WWW Earth’s Interior Crust
The lithosphere includes two different types of silicate CRUST:
> Continental crust – Thicker (35 km avg.) & less dense (more buoyant; higher)
> Oceanic crust – Thinner (7 km avg.) & more dense (less buoyant, lower)

21. WWW Earth’s Interior Mantle
Fe- & Mg-rich silicate rock layer forms most of Earth’s volume
Known only from xenoliths in volcanic rocks, geophysics, and theoretical & lab studies

22. WWW Earth’s Interior Core
P-wave shadow zone due to the Core-Mantle boundary
S-wave shadow zone due to a liquid Fe-rich Outer Core
Some P-waves are faster due to a solid Fe-rich Inner Core

23. Earth’s Interior
Earth’s Interior
Core
The Dynamo Effect: Earth’s magnetic field is generated by a rapidly rotating, electrically-conducting & convecting Outer Core

24. WWW Links in this Lecture
Earth’s Interior
> Seismology -
> Petrology -
> Earth’s gravity field -
> Earth’s magnetic field -
> Seismic waves -
> Magnetic north pole -
> Polarity changes -
> Paleomagnetism -
> Mid-ocean ridges -
> Earth’s interior -
> Lithosphere -
> Asthenosphere -
> Crust -
> Continental crust -
> Oceanic crust -
> Mantle -
> Xenolith -
> Core -
> Shadow zone -
> Dynamo -
> Electrical conductor - > Convection -