ESL 91
FALL, 2001
FOCUS DISCIPLINE RESEARCH PROJECTS
ENVIRONMENTAL SCIENCE

According to the reading "The Causes of Earthquakes," plate tectonics is a new theory that was introduced some 30 years ago. This theory has changed radically the way geologists think about the earth. The earth’s surface is covered by a series of crusted plates. We get the term plate tectonics, which refers to how the earth’s surface is built of plates.

The earth’s crust is like the shell of a cracked egg. The surface of the earth is broken into seven large and many small plates. These plates are approximately miles thick and hundreds or thousands of kilometers wide. The plates move one towards the other very slowly. The movement of the plates is approximately 5 cm each year.

Plate Tectonics is a combination of two early ideas: Continental Drift and Sea Floor Spreading. Continental Drift is the movement of continents over the earth’s surface. Sea Floor Spreading is the creation of a new oceanic crust at mid ocean ridges and the movement of the crust away from the mid ocean.

In the early 1900’s the emergence of this theory of plate tectonics started a revolution in the earth sciences, and it helped scientists to describe the ways in which the tectonics process affects the daily lives of people everywhere. Alfred Wegener found that tropical plants once grew in icy Greenland and the glaciers tense warm Africa and Brazil. His theory was that at one time all the continents may have been united as one continent (called a super continent pangaea) and may have shared a similar climate. Wegener’s idea served to formulate the development of the theory of plate tectonics three decades later; This theory was called Continental Drift.

At present geologists have found clues that the continents move. The first clue is the shape of the continents. They seem to be like puzzle pieces. The second clue comes from rocks. The geologists compared the rocks on different continents and they found that some rocks have similar traces of plants and animals that lived long ago. These fossils were found on the coast of South America and Africa, which are now widely separated by the Atlantic Ocean.

In the 1950’s new evidence emerged around the ocean floor. A new theory called “Sea Floor Spreading” showed that great mountain ranges were found on the sea floor. These mountains were found in the central Atlantic. These are called the global mid - ocean ridges. In some places the mid - ocean ridges show above the Ocean surface. These mountains are more 50.000 Km long, more than 800Km across the continent, and approximately 4.500 meters above the sea floor. This mountain is wider than the Himalayas in size.  

The Ocean Floor continues to move, spread, and shake at the edges and continues to regenerate oceanic ridges and continental drift leading to three fundamental types of plate boundaries, Divergent, convergent and transform-fault. Divergent boundaries occur when two plates are moving apart under the ocean floor. They leave a crack between them where the magma, or melted rock, rise up through the crack. Convergent boundaries move toward each other and collide. When a continental plate collides with an Ocean plate the ocean plate tips down and it gets under the continental plate forming a deep ocean trench. This kind of movement occurs in the ocean plate Nazca and continental south. Transform - fault boundaries occur when two plates move horizontally to one another. The San Andreas fault zone is a good example of this type of movement.

The basic concept of plate tectonics has helped sciences come up with a better explanation for the movement of strong big pieces of the earth’s crust which affect certain areas of the earth. These concepts have also helped us to understand the formation of mountains and the distribution of earthquakes and volcanoes. The connection between plate tectonics and earthquakes is evident. When plates move apart and split past one another it, it causes big earthquakes. One example of this connection between plate tectonics and earthquakes is the San Andreas rift that is found in the North American continent in California. The 1906 San Francisco Earthquake was produced by a great displacement of plates that moved horizontally to one another causing a great destruction in California. The earthquake caused death and material losses.

My Response

This research has helped me understand much better how plate tectonics influences the geological process of the earth. The earth continues to evolve and plate tectonic movements are part of this evolution. The constant changes in plate tectonics don't always produce terrible catastrophes. However many times they produce small changes like tremors and high waves in the ocean. But when the movement is too abrupt or drastic it can produce terrible catastrophes like earthquakes and tidal waves. However it is interesting to learn how they work. Through this research I learned that we don't have control over these huge pieces of solid rock that move around the continents, and I learned how they affect the land where we live.

Based on my own experience, my country Egypt is located in the north of the African continent on the Mediterranean sea.  I remember that we had never gotten any great earthquake. However October 12, 1992 at 3.30 p.m. a great earthquake was registered in the north of Egypt. I remembered that I felt the earth shaking abruptly. Some houses in the street were demolished by the movement and the sound waves. The street cracked and a few cars fell into the crack. People ran in the street, some people were screaming and others crying. It was a very traumatic experience.

Conclusion

In conclusion the earth's surface is covered by a series of crusted plates.  The new theories about plate tectonics explain how this surface is broken and how they move. The earth continues to evolve and plate tectonic movements are part of this evolution. The discoveries of scientists have created new material and new ways of doing things. We and the world where we live are constantly being affected by the changes of science. As a result we need to adapt and to learn to live in harmony with the natural processes of the earth.

Works cited:

Major Tectonics of the World: http://geology.er.usgs.gov/eastern/plates.html

http://wwwneic.cr.usgs.gov/neis/plate_tectonics/plate_tectonics.html

This Dynamic Earth: The Story of Plate Tectonics: http://pubs.usgs.gov/publications/text/dynamic.html

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