Briefly describe the manner in which the
paleomagnetic time scale was derived.
Use sketches.if you wish.Magnetic Polarity Time Scale.
Describe briefly how the fact that the earth's
magnetic field reversed was shown and how the timing of the reversals was
determined. Why was the magnetic
polarity time scale derived by this work carried back only to 4 million
years. Label the epochs and events
on the diagram below.
Briefly describe the contribution Fred Vine &
Drummond Matthews made to the development of the theory of seafloor spreading.
What is the range of spreading rates observed along
the Mid-Ocean Ridge at present? (5 pts.).
Several magnetic anomaly profiles across the
Mid-Ocean Ridge are shown in Figure 2.
Identify the anomalies resulting from the Bruhnes, Matayama, Gauss and
Gilbert epochs, and the Jaramillo, Olduvai, Mammoth, Cochiti, Nunivak, and
"C" events on Figure 2 and show your calculations of half spreading
rates for each profile below. A
time scale is included in Figure 3.
(10 pts.).
Give approximate full spreading rates for the
following (3 pts.):
1. South
Atlantic portion of the Mid-Ocean Ridge.
2. East
Pacific Rise in the south Pacific.
3. Mid-Ocean
Ridge in the Arctic Ocean.
Give approximate half spreading rates for the
following (4 pts.):
Given the following information, calculate half
spreading rates. Show your
calculations. A time scale is
provided at the back of this test.
1. MOR
crest to Brunhes-Matayama boundary is 70 km.
2.
MOR crest to Brunhes-Matayama boundary is 140 km.
3. MOR
crest to Gauss-Gilbert boundary is 330 km.
4. MOR
crest to Gauss-Gilbert boundary is 700 km.
5. MOR
crest to anomaly 5 is 100 km.
6. Width
of seafloor between anomaly 10 on either side of MOR is 600 km.
7. Width
of seafloor between anomaly 32 on either side of MOR is 1600 km.
8. Width
of seafloor from anomaly 32 on the west side of the MOR to anomaly 32 on the
east side of the MOR is 2850 km.
9. Width
of seafloor from anomaly M-25 to anomaly M-16 is 600 km.
Where are slow-spreading ridges found?
Where are fast-spreading ridges found?
What spreading rate divides fast and slow ridges?