Preview - Plate Tectonics: Secrets of the Deep

Plate Tectonics: Secrets of the Deep

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Plate Tectonics: Secrets of the Deep (57:00)

Item# 6148
©1995

Viewed from space, one of the remarkable features of our planet is that it has continents and oceans. The changing pattern of the continents and oceans is a very important characteristic of the earth, and the discovery of how this movement occurs is one of the most exciting scientific stories of modern times. The key to this understanding lay not in the continents at all, but in the oceans. The oceans turned out to have a record of their history as precise as tree rings or a magnetic bar code, and with it came the history of relative motion between the continents. These motions are not fast by our standards, but by geological standards they are very rapid. As a description of what is happening in the oceans, plate tectonics is so simple, powerful, and accurate that it has come to dominate our view of the earth’s behavior. (57 minutes)

Segments in this Video - (14)

1. Movement of Continents (04:47)

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While scientists study the expiration of the oceans, geologic and geographic evidence reveal that continents move within the earth's oceans.

2. Magnetic Field on the Ocean Floor (04:54)

Scientists study the strength of the earth's magnetic field by studying the shape of the sea floor. The outcome of the study is a survey map that shows a magnetic field of varied strength.

3. Magnetism in Rocks (05:43)

Volcanic rocks become magnetized when the iron oxide in them cools. Scientists are able to measure the direction of the magnetic field in rocks and determine when the earth's magnetic field changed.

4. Direction of a Magnetic Field (02:46)

It is possible to make a magnetic field and an electric current at the same time by moving iron through a conductor. When the magnetic field reverses, the electric current does also.

5. Theory of Rock Memory (04:35)

In 1963 Cambridge scientists Vine and Matthews propose a theory of how stripes form on a survey map, which represents the ocean floor and the formation of oceanic mountains.

6. Testing the Theory (04:09)

By studying the pattern of stripes along the ridges in oceans and their magnetic reversals, scientists know how fast earth is being formed in the oceans by the rate at which the ridges are spreading.

7. Seismology (04:34)

Seismology is developed as a science to meet the need for national security. During the 1940s, the U.S. Air Force monitors nuclear explosions in Russia by listening to sounds within the earth.

8. Earthquakes in the Ocean (03:49)

Soon after seismology is invented, the first accurate earthquake maps are created. Most earthquakes occur in the trenches in the Pacific Ocean around the Ring of Fire.

9. Creation and Destruction of Sea Floor (02:30)

An earthquake in Alaska reveals the Pacific Ocean sea floor slid underneath Alaska and lifted up some of the coastal region. The sea floor is created and destroyed around the ocean trenches.

10. Earthquake Plates (03:58)

Earthquakes occur around the trenches or on the mid-ocean ridge systems in very narrow bands around the earth called plates. These plates like the San Andreas fault move around the earth.

11. Measuring the Motion of the Plates (03:28)

Scientists can measure the motion of tectonic plates by satellites that send and record information about precise distances between plates within a centimeter.

12. Solving Ancient Puzzles (02:35)

Based on the theory of plate tectonics, the oceans started spreading 250 million years ago. There is also evidence that ice sheets covered a great deal of the earth 300 million years ago.

13. Process of Creep (04:19)

The sea floor gets pushed down into the earth through a process called creep. Deep in the earth, rocks can flow because they get closer to the melting point as they get hot.

14. Cooling the Earth (02:46)

The earth cools itself when hot rocks move away from the mid-ocean ridges into the trenches and move the plates. This also explains the formation of volcanoes.