A Voyage Through Time

A Voyage Through Time

Background

The movement of the lithosphere has been going on for several hundred million years. Because of this continuous motion the shape and position of land masses (continents and islands) today is much different from their shape and position in the past.

Land masses ride like passengers embedded in the lithosphere. When two plates collide one usually slides beneath the other. At the same time, land masses riding on the plate that is forced downward usually do not sink with the plate. Instead they push up against the land masses riding on top of the other plate. This is one way that mountain ranges are built. Mountain building in this way is occurring today, the Himalayan Mountains are the result of collisions.

About 280 million years ago a number of large land masses came together and formed a supercontinent called Pangaea. Pangaea existed for roughly 80 million years, until the lithosphere plates began to break apart and move away from one another. When the plates moved apart, Pangaea broke into smaller land masses that began to move away from one another also.

Geologists have reconstructed the approximate shape and size of Pangaea by comparing rocks found in today’s continents and oceans. Using different kinds of data, geologists have been able to chart the changing positions and shapes of land masses since Pangaea broke apart.

Plate movement still occurs today, and will occur long into the future. Although continents appear fixed in position, actually they are on the move. If the plates continue on their present course, North America will bump into Asia in a few hundred million years. Australia is heading northeast towards the equator at about the same rate. Africa and Europe continue to move towards each other.

In this activity you will follow the movement of land masses over the past 200 million years, beginning with the break up of Pangaea. A flip book model shows how land masses move and how today’s continents arrived at their current positions.

Procedure

1.  Look at the three map sheets. These are reconstructed maps of land masses that existed on Earth at a specific time. Each frame is 10 million years. Frame 20 depicts land masses close to what they are today.

2.  Beginning with frame 20 and working backward identify the land masses listed in table 1. Color these land masses and label the color in table 1. Continue until you reach frame 1.

Questions/Conclusions

1.  What event began to occur about 200 million years ago?

2.  During your coloring of the frames, in which frame did you locate the first appearance of the following land masses:

a.  North America ______

b.  Australia ______

c.  India ______

d.  Europe ______

e.  Antarctica ______

3.  In which frame did you locate the final breakup of Pangaea? Why did you choose that frame and not another?

4.  What causes continents to move across Earth’s surface?

5.  How might you explain the fact that continents are not submerged when plates collide and one sinks under the other? Explain your reasoning.

6. If mountain ranges can form where plates are colliding, what would you hypothesize might occur where plates are separating? Apply your hypothesis to identify locations on a world map.