Layers of the earth
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plate boundaries
tectonic plates
tectonic plates are pieces of the earths crust and uppermost mantle, together referred to as the lithosphere. the plates are around 62 miles thick and consist of two principle types oceanic crust(in the ocean usually thinner) and continental crust (the land)
plate tectonic theory - plate tectonics is the theory that explains the global distribution of geological phenomena. Principally it refers to the movement and interaction of the earth's lithosphere. This includes the formation, movement, collision, and destruction of plates and the resulting geological events such as seismicity, volcanism, continental drift, and mountain building.
continental drift
continental drift is a theory that explains how continents shift position on the earth's surface. set forth in 1912 by Alfred Wegener, a geophysicist and continental drift also explained why look-alike animal and plant fossils, and similar rock formations, are found in different continents
Earth's structure
mantle
outer core
crust
inner core
a layer of sand and rock varying from 5 - 50 km thick
A rock layer about 2850 km thick that reaches about half the distance to the center of the earth. parts of this layer become hot enough to liquefy and become slow moving molten rock or magma
A mass of molten iron about 2200 km thick that surrounds the solid inner core
A mass of iron with a temperature of 3870°c.normally iron would melt at this temperature, but immense pressure on it which keeps it a solid it is 2400 km in diameter and 6,000 miles below the earth's surface
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constructive
destructive
conservative
A destructive plate boundary is sometimes called a convergent or tensional plate margin. This occurs when oceanic and continental plates move together. The oceanic plate is forced under the lighter continental plate. Friction causes melting of the oceanic plate and may trigger earthquakes. Magma rises up through cracks and erupts onto the surface.
An example of a destructive plate boundary is where the Nazca plate is forced under the South American Plate.
A constructive plate boundary, sometimes called a divergent plate margin, occurs when plates move apart. Volcanoes are formed as magma wells up to fill the gap, and eventually new crust is formed.
An example of a constructive plate boundary is the mid-Atlantic Ridge.
a conservative plate boundary sometimes called a transform plate margin occurs where plates slide past each other in opposite directions, or in the same direction but at different speeds.
Friction is eventually overcome and the plates slip past in a sudden movement. The shockwaves created produce an earthquake.
This occurs at the San Andreas Fault in California.