Lab: The Evidence for Plate TectonicsName: ______

Figure 1: This is a view of the Ocean Floor. Each circle represents a site where a core sample was taken. You can assume that each core shares its properties with the entire section.

Lab: The Evidence for Plate TectonicsName: ______

Figure 1: This is a view of the Ocean Floor. Each circle represents a site where a core sample was taken. You can assume that each core shares its properties with the entire section.

Graph 1: Earthquake Patterns and Trenches(The top of the graph should be considered the surface with a depth of zero)

Graph 1: Earthquake Patterns and Trenches(The top of the graph should be considered the surface with a depth of zero)

Lab: The Evidence for Plate Tectonics

Part 1: Paleomagnetism:

When lava cools, the iron inside of it forms crystals which align themselves with the Earth’s magnetic field as they cool. (Like a tiny compass). Geologists know that Earth’s magnetic field reverses itself every so often, and has done so many times in the past. Reverse magnetism can be seen in ancient volcanic lava flows on land, as well as the ocean floor.

Procedure:

  1. On the core same you have been given, there is an arrow on the top of it indicating which direction North is from the site it was taken. Use your compass to assess whether this sample displays normal or reverse polarity.
  2. Hold the compass directly over the core sample.
  3. If the compasses red arrow points in the same direction as North on the sample it is normal.
  4. If the compass point in the opposite direction as North (South) on the sample then it is reverse.
  5. Find your core sample in Figure 1 above and color its entire section to indicate its polarity. Make sure to use the key to explain your image.
  6. There are five other groups that you will need to collaborate with to fill in the rest of your paleomagnetism data. Discuss and share each group’s results. Make sure to test some of the samples for yourself to see the difference.
  7. Fill in this data on the map above to complete your picture of the ocean floor.

Part 2: Age of the Ocean Floor:

Scientists are able to use a process called radioactive dating to tell how old the ocean floor is. This is based on the natural rate at which certain unstable isotopes breakdown. It is a very accurate way of measuring the age of anything from archaeological finds to rocks. Here are some important facts:

  1. The amount of time it takes for half of the material to breakdown is called the half-life.
  2. We can make measurements to find out how many half-lives have gone by since a rock formed.
  3. If we know the number of half-lives, and the amount of time 1 half-life is equal to we can calculate age. (Age = (The number of half-lives) x (The length of time 1 half is equal to)
  4. To make this simple let’s assume that the half-life of the isotope used in our sample is 10 million years.

Procedure:

  1. Use the number of half-lives to calculate the age of your sample using the simple equation in line 3 above.
  2. Write the age of your sample in the appropriate spot of figure 1
  3. Share information with the other groups to fill in the ages of the rest of the samples.
  4. Using your completed age map, you should be able to accurately guess where an oceanic ridge would be on this map. Remember that new lithosphere is constantly produced along oceanic ridges.
  5. **Draw the oceanic ridge on your map as a chain of mountains and label it clearly.

Part 3: Earthquake Patterns

If new lithosphere is being produced along ridges, then lithosphere must also be destroyed in other places at the same rate. If not, the planet would be growing, and we know that isn’t true. We can use Earthquake data to find places around the world where this is happening. Anyplace where lithosphere is descending into the mantle would show an Earthquake pattern of progressively deeper Earthquakes. Let take a look at this pattern along the trench that is labeled in figure 1.

Procedure:

  1. Using the Table 1, plot each Earthquake on Graph 1.
  2. The top of your graph should be a depth of 0
  3. Choose an appropriate scale for the y-axis
  4. The numbers (depth) should increase as your go down.
  5. On the X-axis the scale should be 25km per square
  6. Make sure to include all appropriate labels etc.

Table 1: Earth depth and distance from Trench

Quake / Focus Depth (km) / Distance from trench (km)
A / 55 / 0
B / 295 / 100 east
C / 195 / 65 east
D / 695 / 400 east
E / 20 / 40 west
F / 520 / 390 east
G / 480 / 285 east
H / 665 / 545 east
I / 85 / 25 west
J / 635 / 665 east
J / 55 / 95 west
L / 70 / 100 west

Conclusion: Write and answer the following questions on the back of your map/graph

  1. What is paleomagnetism? (Part 1)
  2. Explain how the age of the ocean floor is evidence for plate tectonics. (Part 2)
  3. Explain how the depth of Earthquakes changes as we get further from a trench. (Part 3)
  4. These are 3 lines of evidence for plate tectonics. What is the fourth we learned about and explain why it is considered evidence?
  5. Your map and activity for parts 1 and 2 showed two types of plate boundaries today. Of the 3 boundary types we have learned which 2 were studied today?
  6. Name and describe the third type of plate boundary which we did not study today.
  7. On the east side of your map is a trench. (In parts 1 and 2) What geologic feature would we expect to see to the east of the trench (in parts 1 and 2)?
  8. In part 3 your trench is on the opposite side. Which direction (east or west) is the subducting plate moving? Explain your answer

REVIEW

  1. This lab was about evidence for plate tectonics, what are 4 lines of evidence for continental drift?
  2. Who came up with the hypothesis of Continental Drift?
  3. What is the name he gave to his hypothesized super continent?