The Plate Tectonics Theory

For millions of years, tectonic plates have been determinate of changes in the physical face of the earth, and they continue to do so today. These massive plates move underneath the surfaces of the oceans and the continents, producing earthquakes, volcanoes and uplifts. This paper will discuss the composition, movement and history of tectonic plates, the theory of plate tectonics and its history, and tectonic plates affect the surface of the earth today and will continue to do so in the future.

The earth is divided into three main layers: the core, the mantle and the crust. The core is further divided into the solid inner core and the liquid outer core. This layer is mostly iron and nickel and is extremely hot. The mantle is divided into the lower and upper mantle and is composed mostly of iron, magnesium, silicon, and oxygen. The outermost layer, which contains all life on earth, is the crust. This layer is rich in oxygen and silicon as well as aluminum, iron, magnesium, calcium, potassium, and sodium. It is in between the crust and the mantle that we find tectonic plates. The outermost layers of the earth are divided into two categories based on their physical properties. The asthenosphere is the lower of these categories, composed of clastic or flowing mantle. The upper layer is known as the lithosphere and contains both the top, rigid layer of the mantle and the crust. The lithosphere is what makes up the tectonic plates. The composition of these plates is based on their location. Plates under the surface of the ocean are made of mostly of basalt, while continental plates are comprised of rocks such as andesite and granite.

It is generally believed that there are 12 plates that make up the earth's surface. The majority of these plates are a combination of oceanic and continental lithosphere, while the Nazca, Pacific and Juan de Fuca Plates are made up of mostly oceanic lithosphere. Most of the continents have their own plate or plates, with the exception of Europe and Asia, which share the massive Eurasian Plate. Along the edges of these plates there is a large occurrence of geologic activity. "Earthquakes and volcanoes, evidence of unrest in the Earth, help locate the edges of plates." This unrest is caused by movement of the plates, which can be broken down into three general types. A divergent plate boundary is where the plates are pulling and moving away from one another. An example of this is the Mid-Atlantic ridge. Conversely, the Western banks of South America show evidence of convergent plate boundary, where the plates are pushing and moving towards one another, in this case the Nazca and South American Plates. The last type of boundary is a transition, which is illustrated by the San Andreas Fault in California. In this case, the edges of the plate are sliding past each other.

Tracking the movement of the plates is often done by tracking the distance between two objects on different plates. This allows geologists to see how far the plates have moved towards or away from each other. Unfortunately this does not allow for absolute tracking of a single plate. With the advent of GPS or Global Positioning System, geologists can use satellites to track the absolute position of a plate. There are currently 21 satellites being used by the United States, and each of these can be and are being used to track plate locations and movements. This is still a relatively new technology and will most likely be used more and more as the science is perfected.

The theory of plate tectonics suggests that the surface of the earth is broken into massive plates and these plates slowly drift towards and away from each other. When the edges of these plates meet, they produce intense activity, marked by earthquakes and other geological events. The plate tectonics theory is a combination of two other theories: continental drift and sea-floor spreading.

Alfred Weneger, a German meteorologist, first hypothesized about continental drift in 1912. After noticing that there were certain fossils that appeared on almost every continent, Weneger proposed the idea that all these fossils were once on a single continent and that the single continent (or Pangaea) had drifted apart to form the 7 present-day continents. His hypothesis was strengthened by the fact that rock sequences in South America, Africa, India, Antarctica, and Australia showed three identical layers, and by the likelihood that these layers were formed all at once and later broke apart when the continents began to drift. Also, similar glacial grooves on the southern tips of South America, Africa, India and Australia further the idea that the grooves were formed by a glacier when these 4 continents were connected to the northern section of Antarctica. The only real shortcoming of Weneger's theory was that he provided no real reason for the drift of the continents except the spinning and rotation of the earth. He suggested that the continents plowed through the oceanic plates with sheer force. American geologists found that theory highly unlikely and Wenger's work was widely discredited in America.

The theory of sea-floor spreading was proposed in 1962 by geologist Harry Hess. This theory suggests that there are convection currents that push