Welcome to Our Plate Tectonics Page!
On this page you will find information about the layers of the earth, convection in the mantle, and sea-floor spreading.
Section A: Inside the Earth
Section B: Convection in the Mantle
Heat Transfer
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Section C: Sea Floor Spreading
What is the Process of Sea-Floor Spreading?
By: Megan
The process of sea-floor spreading begins along a mid-ocean ridge. Mid-ocean ridges are located on a divergent boundary. This means that the two plates move away from each other. Molten material in the mantle then builds up several kilometers beneath the surface. The molten material will then rise and erupt. At the same time, the older rock moves away from the ridge, carried by the divergent plates. As the material cools down, it hardens into a type of rock called basalt and forms a new strip of rock. Basalt is what the oceanic crust is mainly made up of. Sea-floor spreading generally adds about 4-5 centimeters of new rock per year to the ocean floor. Two examples of mid- ocean ridges are the Mid-Atlantic Ridge and the East Pacific Ridge (also known as the East Pacific Rise).
Subduction at trenches
By: Chloe c. and carlee
The ocean floor actually does not keep spreading. The ocean floor actually plunges into deep underwater canyons called deep ocean trenches. Deep ocean trenches form where the oceanic crust bends downward. If there are deep ocean trenches, subduction always takes place. Subduction is the process when the ocean floor sinks beneath a deep ocean trench and back into the mantle. Convection currents that are under the lithosphere push new crust that is forms at the mid ocean ridge towards deep ocean trenches. New oceanic crust is hot, but as it is moving away from the mid ocean ridge, it becomes cooler and more dense. The, gravity pulls the older, cooler, denser oceanic crust below the deep ocean trench. At deep ocean trenches, subduction allows part of the ocean floor to sink back into the mantle. This takes tens of millions of years. Once the oceanic crust gets to the deep ocean trench, it is destroyed.
Evidence of Sea-floor Spreading
By: krista
Some evidence of seafloor spreading are the magnetic stripes in the ocean floor, the ages of the rock, and the formations of the molten material. A few of the scientists that studied seafloor spreading are Fred Vine, Drummond Matthews, and Harry Hess. In the late 1900s, they found that rock around mid-ocean ridges have alternating bands. This happened because of the reversal of the Earth’s poles (north and south). The iron bits in the molten material lines up with the poles. When it cools and hardens, the iron bits are locked in place permanently. Samples of the ocean floor show that the oceanic crust is younger because it is closer to the mid ocean ridge. Using the drilling ship called the Glomar Challenger to collect samples, scientists found that the farther the rock is from the mid-atlantic ridge, the older it is. This also proved that seafloor spreading took place. In the 1960’s, scientists found more evidence of seafloor spreading. They used a submarine called Alvin that was specially built to withstand underwater pressure in order to take a look at the ocean floor. They then found rocks shaped like pillows or pinched tubes. The only way that these rocks could have formed is by having molten material quickly harden after erupting underwater.
Link for Animation:
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3D Model
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Section d: The theory of plate tectonics
THE THEORY OF PLATE TECTONICS AND WEGNER'S THEORY
By: Taryn and jenefer
The theory of plate tectonics depends greatly on Alfred Wegner’s theory of continental drift, since plate tectonics are the reason for the shifting of the continents. Continental drift states that all the continents were once connected in a single landmass, Pangea, that has since drifted apart. His evidence to support the theory includes land feature, climate change, and fossil evidence. Not only were similar geographical features found on different continents, the continents lined up almost perfectly. Also, common fossils were found on many of the continents, some of which would be impossible without climate change or travel over the connected continents.
Paragraph By: Taryn and Jenefer
Paragraph By: Taryn and Jenefer
THE THREE TYPES OF PLATE BOUNDARIES
By: eleu
There are three types of plate boundaries: convergent, divergent, and transform.
Convergent boundaries are two plates that collide, or move together. They form volcanoes and earthquakes. When two plates move together, or converge, a convergent boundary takes place. Convergent boundaries are the cause of most volcanoes and mountains.
Divergent boundaries take place when two plates move apart, or diverge. These boundaries usually happen along mid-ocean ridges, and form rift valleys.
Transform boundaries occur when two plates slide past each other. When the two plates grind past each other, great amounts of energy build up, and are sometimes released in the form of large earthquakes. Transform boundaries are also the cause of most fault lines.
Paragraph and Picture By: Taryn and Jenefer
Convergent boundaries are two plates that collide, or move together. They form volcanoes and earthquakes. When two plates move together, or converge, a convergent boundary takes place. Convergent boundaries are the cause of most volcanoes and mountains.
Divergent boundaries take place when two plates move apart, or diverge. These boundaries usually happen along mid-ocean ridges, and form rift valleys.
Transform boundaries occur when two plates slide past each other. When the two plates grind past each other, great amounts of energy build up, and are sometimes released in the form of large earthquakes. Transform boundaries are also the cause of most fault lines.
Paragraph and Picture By: Taryn and Jenefer