1. EXPLORING EARTH’S INTERIOR
Grotzinger • Jordan
Understanding Earth
Sixth Edition
Chapter 14:
EXPLORING EARTH’S INTERIOR
© 2011 by W. H. Freeman and Company

2. Exploring Earth’s Iinterior
Chapter 14
Exploring Earth’s Iinterior

3. About Earth’s Interior
The center of the Earth is about 6,400 km below us … the deepest well is 10 km.
Heat inside the Earth drives the core’s geodynamo and the mantle’s convection.
Earth’s interior is explored by using information from seismic waves and their passage through the body of the Earth.

4. Lecture Outline 1. Exploring the interior with seismic waves
2. Layering and composition of the Earth’s interior
3. Earth’s internal temperature
4. Visualizing Earth’s 3-D structure

5. Lecture Outline
5. Earth’s magnetic field and the geodynamo

6. Exploring the Interior
with Seismic Waves
● Basic types of waves
● compressional (P waves)
● shear (S waves)
● Reflection and refraction

7. Exploring the Interior
with Seismic Waves
● Paths of seismic waves
● wave bending
● shadow zones (P and S)
● reflection at internal boundaries

9. P- and
S-wave
paths
from an
earthquake

10. P-, S-, and surface-wave
paths: from focus to seismograph

11. P, S, and surface waves
recorded on a seismograph

12. 2. Layering and Composition
of the Interior
● Seismology model of Earth’s layers
● crust and lithosphere
● asthenosphere
● mantle with internal phase
change at 400 km

13. 2. Layering and Composition
of the Interior
● Seismology model of Earth’s layers
(continued)
● core-mantle boundary
● core (inner and outer core)

14. Earth’s
layering
revealed by
seismology

15. Earth’s
mantle
structure
beneath an
old ocean
basin:
S-wave
velocity to
depth of
900 km

16. Thought questions for this chapter
The Moon shows no evidence of tectonic plates or their motions, nor has it been volcanically active for billions of years. What does this observation imply about the state and temperature of the interior of this planetary body?
How do the existence of Earth’s magnetic field, iron meteorites, and the abundance of iron in the cosmos support the idea that Earth’s core is mostly iron and the outer core is liquid?
How would you use seismic waves to find a chamber of molten magma in the crust?

17. ● Heat flow through Earth’s interior ● conduction (lithosphere)
3. Earth’s Internal Temperature
● Heat flow through Earth’s interior
● conduction (lithosphere)
● convection (mantle and core)

18. Topography
of mid-ocean
ridges in the
Atlantic and
Pacific oceans

19. ● Temperatures in the Earth ● geothermal gradient
3. Earth’s Internal Temperature
● Temperatures in the Earth
● geothermal gradient
● normally 20 to 30ºC / km
● 13001400ºC at base of
lithosphere
● 30006000ºC + in core

20. An estimate
of the geotherm:
temperature
increase with
depth in the
Earth

21. ● Earth’s gravity field ● The geoid
4. Visualizing Earth’s 3-D Structure
● Seismic tomography
● Earth’s gravity field
● The geoid

22. Mantle structure

24. The geoid:
shape of planet Earth

25. Thought questions for this chapter
How would seismic tomography answer the question, “How deep do the subducted slabs go before they are assimilated?”
Where in the mantle might you look to find regions of anomalously low S-wave speeds?

26. 5. Earth’s Magnetic Field and Geodynamo
● Earth’s dipole field
● complexity of the magnetic
field
● non-dipole field
component
● secular variations in the
● magnetic reversals

27. Change
in the
location
of the
North
magnetic
pole from
1600 to
2000

28. 5. Earth’s Magnetic Field and Geodynamo

29. 5. Earth’s Magnetic Field and Geodynamo

30. 5. Earth’s
Magnetic
Field
and
Geodynamo

31. Earth’s
magnetic
field
lines

32. Earth’s
magnetic
field
reversals:
Step 1

33. Earth’s
magnetic
field
reversals:
Step 2

34. Earth’s
magnetic
field
reversals:
Step 3

35. Earth’s
magnetic
field
reversals:
Step 4

36. ● records of magnetization ● thermoremanent ● depositional remanent
5. Earth’s Magnetic Field and Geodynamo
● Paleomagnetism
● records of magnetization
● thermoremanent
● depositional remanent
● magnetic stratigraphy

37. Thermoremanent

38. Depositional remanent

39. Paleomagnetic time scale

40. ● Magnetic field and the biosphere ● magnetic orientation
5. Earth’s Magnetic Field and Geodynamo
● Magnetic field and the biosphere
● magnetic orientation
● magnetic frame of reference
● field offers protection from
the solar wind

41. Key terms and concepts Conduction Convection Core-mantle boundary
Compression wave
Conduction
Convection
Core-mantle boundary
Depositional remanent magnetism
Dipole
Geotherm
Isostasy
Low-velocity zone
Lower mantle
Mohorovičić discontinuity
Paleomagnetism
Phase change
Seismic tomography
Shadow zone

42. Key terms and concepts Thermoremanent magnetization Transition zone
Shear wave
Thermoremanent magnetization
Transition zone
Upper mantle