Science

December 7, 2016 General Studies

My model is of sea floor spreading and subduction, with minor folds, erosion and sedimentation.

The lithosphere, the outer hard shell of the Earth, is broken into a dozen or so major pieces, called plates, and these plates are moving with respect to one another. At one time North America, South America, Europe, and Africa were joined together in one giant continent that has since broken apart to form the Atlantic Ocean Basin. .

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Sea-floor spreading is the process in which the ocean floor is extended when two plates move apart. As the plates move apart, the rocks break and form a crack between the plates. Earthquakes occur along the plate boundary. Magma rises through the cracks and seeps out onto the ocean floor like a long, thin, undersea volcano.

When North and South America moved away from Europe, the resulting crack was filled by mantle material, which cooled and formed a new lithosphere. This process still continues today. Molten mantle materials continually rise to fill the cracks formed as the plates move slowly apart from each other. This is forming an underwater mountain chain, known as the mid ocean ridge. .

Most sedimentary rocks are laid down as horizontal beds. If, however, they are subjected to severe pressures, at plate boundaries for example, they may suffer folding and faulting. The style of these structures depends on the rock types themselves, but also the degree of pressure and temperature. Sometimes folding can result in steeply dipping layers. Faulting can occur because of compress ional pressures attempting to squash the rocks, or because of tensional forces trying to pull them apart. Most of the faults in the British Isles are the result of stresses which existed in the past. As a result they are now more or less inactive. In some parts of the world, however, active faults are the source of major earthquakes, e.g. the San Andreas Fault in California.

Sedimentation happens over millions of years as build up of animal and plant remains decompose and form layers.

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