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, magnetic reversals are recorded in ferromagnetic rocks. Seafloor is made of basalt which is ferromagnetic and can record the Earth's magnetic field at the time of its formation.
2. For the second question, the magnetic stripe pattern on each side of the Oceanic Ridge is symmetrical. This is because new seafloor is formed symmetrically on both sides of the ridge as magma rises and solidifies.
3. For the third question, the symmetrical magnetic stripe pattern suggests that the seafloor spreads from the mid - oceanic ridge. New oceanic crust is continuously formed at the ridge and moves away from it symmetrically, recording the Earth's magnetic field reversals as it cools and solidifies.

Answer:

1. Basalt (a type of ferromagnetic rock).
2. The magnetic stripe pattern is symmetrical on each side of the Oceanic Ridge.
3. The seafloor spreads from the mid - oceanic ridge.