Download Geography 12

Geography 12
Plate Tectonics: Sea Floor Spreading
Purpose: to study the method by which the rate of sea floor spreading can be determined.
The date you will plot was obtained using a Magnetometer. The device was towed behind
a ship and measured the intensity of the magnetism locked in the rocks of the sea floor. It
has been noted that the magnetism of the earth has reversed direction several times in the
earth’s past. The times of these reversals are known. From this type of data, the
knowledge of sea floor spreading and the rate of spreading can be gained.
Background Information
The magnetosphere can flip its orientation, so that the field lines which were pointed
toward the North Pole change and point toward the South Pole. On Earth, the record of
the reversal of the magnetic field is preserved in the magnetic rocks – in most cases it is
black rock known as basalt, which lie along the ocean floor. Its magnetization is in the
direction of the local magnetic force at the time when it cools down.
Instruments can measure the magnetization of basalt. Therefore, scientists can
analyze the magnetizations of the various flows and from them get an idea on how the
direction of the local Earth's field varied in the past. As the "plates" on each side are
pulled away, lava emerges from the middle, solidifies and "records" the prevailing
magnetic field. The newly formed basalt sticks to the plates and is also pulled away-some of it towards Europe and Africa, some towards America. Every half million years,
on the average, the Earth's magnetic polarity reverses, and so does the magnetization of
the ocean floor. Each strip therefore represents an epoch of one or the other magnetic
polarity, and the symmetry is also explained. Similar magnetic strips were also observed
in all other oceans.
Procedures:
1. Plot the following stations by latitude and longitude on the map provided. Use the
symbol given for each station.
2. When you have plotted all the data, draw a “best fit” straight line connecting the
stations of present age.
3. Next draw two best fit lines for the 10 million year stations.
4. Next connect the 5 MY symbols. Use a different colour for this line
5. At the North End of each line label the corresponding age. Note you should have
two lines labeled 5 MY, two lines labeled 10 MY and one line labeled Present.
Plotting Coordinates
Station
1
North Latitude
58.0
West Longitude Symbol
29.0
O
Age
10 MY
2
58.5
29.5
R
5 MY
3
58.5
31.0
X
PRESENT
4
59.0
32.0
R
5 MY
5
59.0
34.0
O
10 MY
6
61.0
31.0
O
10 MY
7
60.0
30.0
R
5 MY
8
60.0
29.0
X
PRESENT
9
59.5
28.5
R
5 MY
10.
59.0
27.5
O
10 MY
11.
61.0
24.5
O
10 MY
12.
61.0
26.0
R
5 MY
13.
61.5
26.5
X
PRESENT
14.
62.0
27.0
R
5 MY
15.
62.0
29.0
O
10 MY