Title: the DISTANCE BETWEEN US and THEM SEA FLOOR SPREADING

Title: the DISTANCE BETWEEN US and THEM SEA FLOOR SPREADING

Title: THE DISTANCE BETWEEN US AND THEM – SEA FLOOR SPREADING

INTRODUCTION:

PURPOSE: To visualize sea floor spreading.

BACKGROUND: After Alfred Wegener’s idea of Continental Drift became widely accepted, other scientists began to wonder what was going on under the Atlantic Ocean. Since the Atlantic Ocean did not exist before Pangaea broke apart, they thought something must be happening there. The idea was called Sea Floor Spreading and is the idea that new rock is being added to the Atlantic Ocean bottom.

Sea Floor Spreading occurs at the mid-Atlantic ridge (MAR), also known as the mid-ocean ridge. At the MAR, new material is constantly being added to the ocean floor when molten material from the mantle pushes up. As it does so, it forces the crust apart, then fills in the gap. This creates a series of mountains on either side of the MAR. Since the MAR runs almost the entire length of the Atlantic Ocean, the MAR is considered the longest mountain range in the world.

1.  ROCK AGES

A.  Identical Pattern – The youngest rocks on the Atlantic Ocean bottom are located at the mid-Atlantic ridge. The rocks get older and older and older as you move outward on both sides of the ridge. The oldest rocks on the Atlantic Ocean bottom are located next to the continents. This means that new rocks are forming on the Atlantic Ocean bottom.

B.  Age Compared to Continents – The oldest rocks found on the bottom of the Atlantic Ocean are 200 million years old and are right next to the continents. This is interesting because Pangaea broke apart 200 million years ago. Also, the oldest rocks that can be found on the continents are 4.6 billion (4600 million years old!) This means that new rocks are forming on the Atlantic Ocean bottom.

2.  MAGNETIC REVERSALS – The rocks on the bottom of the ocean are rich in iron. This means they are magnetic. When the rocks cool from a liquid to a solid, all of their particles will line up facing magnetic north. Scientists know that Earth’s magnetic field has reversed itself several times. When the rocks on the bottom of the Atlantic Ocean were analyzed, a pattern of reverse and normal polarity was found. This means that new rocks are forming on the Atlantic Ocean bottom.

Again, once there was a lot of evidence, scientists had no choice but to accept the idea that sea floor spreading is happening.

HYPOTHESIS: If sea floor spreading is modeled, then students will be able to visualize what is happening on the mid-Atlantic ridge.

EXPERIMENTAL PROTOCOL:

MATERIALS: one half file folder ruler colored pencils

scissors masking tape transparent tape

sheet of paper

PROCEDURE:

1.  Figure 1Set up the half file folder so that it looks like Figure 1 below. Draw the lines darkly and label. (You do not need to label the measurements.)

2.  With a pair of scissors, cut the vertical lines so there will be three slits on the half file folder all the same height and parallel to each other.

3.  On the second sheet of paper draw 11 bands each 2.54 cm (1 "wide) perpendicular to the long edge of the paper.

4.  Color the bands you have drawn with alternating colors.

a.  One represents normal polarity – magnetic North where it currently is, at the North Pole. The other represents reverse polarity – magnetic North at the South Pole.

b.  Make the band on the far left, reverse polarity.

5.  Cut the paper in half parallel to the long edge to get two strips of paper as shown in Figure 2.

a.  Mark the bands on each strip with arrows to indicate alternating periods of normal (up arrow) and reversed (down arrow) polarity.

b.  Make sure the band on the far left is reverse polarity.

6.  Insert one end of each strip of paper through the spreading center line (mid-ocean ridge) on your first piece of paper as shown in Figure 3.

7.  Pull each strip of paper through the slits nearest the margins of the paper (the subduction zones).

8.  Tape each strip with transparent tape to itself to make a loop as shown in Figure 3. Overlap the ends showing reverse polarity.

9.  Circulate the ribbons of paper (which represent oceanic crust) to simulate the movement of ocean floor from the mid-ocean spreading center to the subduction zone.

10. Start the movement of the ribbons with bands representing normal polarity touching at the center of the mid-ocean ridge.

RESULTS: See model.

ANALYSIS: (Answer using complete sentences and actual data.)

1.  Why is the fact that new rocks are forming on the ocean bottom critical as evidence for sea floor spreading?

2.  New material is being added to the ocean floor at the mid-Atlantic ridge. Does this mean the Earth is continually growing larger? Explain why or why not.

3.  Draw a side view of what the Atlantic Ocean bottom looks like. Label the mid-Atlantic ridge, continental shelves, and draw arrows to show the direction of plate movement. Label “newly formed rocks,” “50 million years old,” “100 million years old,” “150 million years old,” and “200 million years old” on both sides of the MAR to show the identical pattern of rock ages on both sides. Make a key and color the rocks of different ages (with colored pencils), different colors.

4.  Draw a top view of what the Atlantic Ocean bottom looks like. Label the mid-Atlantic ridge, continental shelves, and draw arrows to show the direction of plate movement. Label “newly formed rocks,” “50 million years old,” “100 million years old,” “150 million years old,” and “200 million years old” on both sides of the MAR to show the identical pattern of rock ages on both sides. Make a key and color the rocks of different ages, different colors. (Use the same colors as above.)

ANALYSIS: (Answer using complete sentences and actual data.)

1.  Why is the fact that new rocks are forming on the ocean bottom critical as evidence for sea floor spreading?

Without this new material forcing its way up to the surface there would be no way for the continents to be pushed apart

2.  New material is being added to the ocean floor at the mid-Atlantic ridge. Does this mean the Earth is continually growing larger? Explain why or why not.

It is not growing larger b/c the plates are being recycled (pulled under ) on the other side

3.  Draw a side view of what the Atlantic Ocean bottom looks like. Label the mid-Atlantic ridge, continental shelves, and draw arrows to show the direction of plate movement. Label “newly formed rocks,” “50 million years old,” “100 million years old,” “150 million years old,” and “200 million years old” on both sides of the MAR to show the identical pattern of rock ages on both sides. Make a key and color the rocks of different ages (with colored pencils), different colors.

4.  Draw a top view of what the Atlantic Ocean bottom looks like. Label the mid-Atlantic ridge, continental shelves, and draw arrows to show the direction of plate movement. Label “newly formed rocks,” “50 million years old,” “100 million years old,” “150 million years old,” and “200 million years old” on both sides of the MAR to show the identical pattern of rock ages on both sides. Make a key and color the rocks of different ages, different colors. (Use the same colors as above.)