Mass of the Earth

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) Inclination (degrees) 300 -54 250 -56 190 -55 160 -50 140 -38 80 0 60 +10 present +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) Declination Inclination (degrees) (degrees) Present 0 +36 25 6 +26 40 10 +19 65 10 -6 100 10 -38 140 190 +61 160 10 -69

Calculate paleolatitudes. Plot the paleolatitudes against time. What can you deduce about the movement of the continent?