Question

seafloor magnetic stripes plotting exercise
name____
procedure:

1. in the lower grid, plot the 20 points listed in the data table on the right.
2. in the box above the grid, draw a geomagnetic reversal timescale from the data plotted on the grid. to do this, use the data plotted on the grid to estimate the distances where the magnetic field switched its polarity (hint: every time the vgp latitude crosses 0 is a change in polarity). shade in periods of normal polarity black, and let periods of reverse polarity be white. (note: in the next lecture we will learn that distance corresponds to seafloor age).

questions:

1. if magnetic reversals are recorded in the seafloor, what kind of rock must the seafloor be made of?
2. what do you notice about the magnetic stripe pattern on each side of the oceanic ridge?
3. what does this pattern suggest about how the seafloor forms?

data table
distance from oceanic ridge (km) | vgp latitude (deg.)
-156 | 82.9
-133 | -88.5
-125 | -80.5
-109 | 71.1
-85 | -82.9
-76 | 12.7
-52 | 38.8
-39 | 86.9
-19 | 82.2
-8 | 60.4
10 | 58.4
21 | 84.0
38 | 87.4
60 | 40.2
76 | 9.6
87 | -83.2
111 | 69.7
128 | -78.8
136 | -87.8
159 | 81.3
polarity
vgp latitude (degrees)
distance from oceanic ridge (km)

Explanation:

1. For the first question, rocks that can record magnetic reversals are magnetic rocks. Basalt is a common magnetic rock on the seafloor as it contains iron - rich minerals that can align with the Earth's magnetic field as it cools and solidifies.
2. For the second question, the magnetic stripe pattern on each side of the oceanic ridge is symmetrical. This means that the distance and polarity of the stripes on one side mirror those on the other side.
3. For the third question, the symmetrical magnetic stripe pattern suggests that the seafloor forms by a process of sea - floor spreading. New oceanic crust is continuously created at the mid - ocean ridges, and as it moves away from the ridge, it records the Earth's magnetic field at the time of its formation.

Answer:

1. Basalt (a magnetic rock containing iron - rich minerals).
2. The magnetic stripe pattern on each side of the oceanic ridge is symmetrical.
3. The seafloor forms by sea - floor spreading.