Download Lab 8

EAS-450 – Physics and Chemistry of the Earth
LAB 8 - Geomagnetism
Objective: Manipulate basic concepts about the Earth’s magnetic field.
1. The declination of a lava is 8 degrees. Give at least 2 possible explanations why it is not zero.
2. The Earth’s magnetic field is similar to the field that would be produced by a huge bar
magnet at its center. Give 2 reasons why it cannot be a magnet.
3. Two rocks have the same iron content, yet their remanent magnetization differ in strength.
Give at least 3 reasons why the strength of the remanence of a rock does not depend just on
its iran content.
4. An American geologist, finding on arrival to New Zealand that his compass does not rotate
freely, sues the airline for damage in transit. What alternate explanation can you offer?
5. A rock magnetized when it was at 20 degrees south of the equator has drifted to 20 degrees
north today. By how much does its inclination differ from that of its present position.
6. A small area of a continent has rocks of a range of ages. Their paleomagnetic directions were
measured (dates are accurate to 4 My, paleomagnetic directions to 2 degrees):
Age (Ma)
300
250
190
160
140
80
60
present
Inclination
(degrees)
-54
-56
-55
-50
-38
0
+10
+43
Calculate paleolatitudes.
Plot the paleolatitudes against time.
What can you deduce about the movement of the continent?
7. A small area of a continent has rocks of a range of ages. Their paleomagnetic directions were
measured (dates are accurate to 4 My, paleomagnetic directions to 2 degrees):
Age (Ma)
Present
25
40
65
100
140
160
Declination
(degrees)
0
6
10
10
10
190
10
Calculate paleolatitudes.
Plot the paleolatitudes against time.
What can you deduce about the movement of the continent?
Inclination
(degrees)
+36
+26
+19
-6
-38
+61
-69