Intro into Plate Tectonics

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Scientific Law Statement that describes an observed phenomenon but does not explain how or why it occurs. It is supported by evidence collected from repeated observations from and experiments performed by many different people. An example would be Newton’s law of gravity or laws of motion.

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Plates The Earth’s surface is broken into many large pieces called plates (also called tectonic or lithospheric plates). The plates move over the asthenosphere.

Continental Plates Thick plates made of andesite and granite that form the continents and are less dense than oceanic plates.

Oceanic Plates Thin plates that are made of basalt that form the ocean floor and are denser than continental plates.

Tectonics Structural deformation of the Earth's crust (Note: prefix “de” means to undo)

Theory of Plate Tectonics Scientific theory explaining how the plates move on the Earth’s surface

Earth is broken into two zones: the upper, thinner, rigid lithosphere 100 km or less in thickness and the lower, more ductile asthenosphere. The tectonic plates are part of the upper lithospheric layer.

The lithospheric plates "float" on the lower, hotter layer called the asthenosphere. This hot, plastic asthenosphere pushes hot, partially molten material at the oceanic ridge and continental rift zones. Cold, dense oceanic slabs sink back down into the mantle in zones where plates meet. The forces from these convection currents are enough to move continental masses 2–15 cm a year.

The theory of plate tectonics is an explanation that the Earth's crust is broken up into seven major and many smaller tectonic plates that move over the surface of the Earth. These tectonic plates are massive, irregularly shaped slabs of solid rock. The smaller plates are only a few hundred km in diameter, while the major plates are thousands of km in diameter.

Plate thickness is variable, from less than 15 km at the oceanic ridges to over 200 km beneath the Himalayan Mountains. With the exception of the one huge oceanic plate and a few of the smaller plates, these plates consist of both oceanic and continental crust and upper mantle material.