Grotzinger • Jordan
Understanding Earth
Sixth Edition
Chapter 14:
EXPLORING EARTH’S
INTERIOR
© 2011 by W. H. Freeman and Company
Chapter 14
Exploring
Earth’s
Iinterior
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.
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
Lecture Outline
5. Earth’s magnetic field and the
geodynamo
1. Exploring the Interior
with Seismic Waves
● Basic types of waves
● compressional (P waves)
● shear (S waves)
● Reflection and refraction
1. Exploring the Interior
with Seismic Waves
● Paths of seismic waves
● wave bending
● shadow zones (P and S)
● reflection at internal boundaries
P- and
S-wave
paths
from an
earthquake
P-, S-, and surface-wave
paths: from focus to seismograph
P, S, and surface waves
recorded on a seismograph
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
2. Layering and Composition
of the Interior
● Seismology model of Earth’s layers
(continued)
● core-mantle boundary
● core (inner and outer core)
Earth’s
layering
revealed by
seismology
Earth’s
mantle
structure
beneath an
old ocean
basin:
S-wave
velocity to
depth of
900 km
3. Earth’s Internal
Temperature
● Heat flow through Earth’s
interior
● conduction (lithosphere)
● convection (mantle and
core)
Topography
of mid-ocean
ridges in the
Atlantic and
Pacific oceans
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
An estimate
of the geotherm:
temperature
increase with
depth in the
Earth
4. Visualizing Earth’s 3-D Structure
● Seismic
tomography
● Earth’s gravity field
● The geoid
Mantle structure
The geoid:
shape of planet Earth
5. Earth’s Magnetic Field and
Geodynamo
● Earth’s dipole field
● complexity of the magnetic
field
● non-dipole field
component
● secular variations in the
field
● magnetic reversals
Change
in the
location
of the
North
magnetic
pole from
1600 to
2000
5. Earth’s Magnetic Field and
Geodynamo
5. Earth’s Magnetic Field and
Geodynamo
5. Earth’s
Magnetic
Field
and
Geodynamo
Earth’s
magnetic
field
lines
Earth’s
magnetic
field
reversals:
Step 1
Earth’s
magnetic
field
reversals:
Step 2
Earth’s
magnetic
field
reversals:
Step 3
Earth’s
magnetic
field
reversals:
Step 4
5. Earth’s Magnetic Field and Geodynamo
● Paleomagnetism
● records of magnetization
● thermoremanent
● depositional
remanent
● magnetic stratigraphy
Thermoremanent
Depositional remanent
Paleomagnetic time scale
5. Earth’s Magnetic Field and Geodynamo
● Magnetic field and the
biosphere
● magnetic orientation
● magnetic frame of
reference
● field offers protection from
Key terms and concepts
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
Key terms and concepts
Shear wave
Thermoremanent magnetization
Transition zone
Upper mantle