Plate Tectonics - Revision Notes

Restless Earth

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  • Created by: Millie
  • Created on: 02-04-13 08:52
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4/6/12 12:05 PM
The Earth is divided into four main layers, the crust, the mantle, the outer core and
the inner core.
Crust: The crust is solid and is the layer we live on. The crust is usually between
10km and 60km thick. The crust thickness is often referred to as the relative
thickness of an apple skin (when compared to the size of an apple).
Mantle: This the thickest section of the earth with a diameter of about 2900km.
The mantle is often described as being semi-molten, but in reality the top is hard
rock and as you near the outer core it is beginning to melt (magma). Convection
currents are found in the mantle.
Outer Core: This layer is believed to be liquid and largely made of iron and nickel. I
is extremely hot with temperatures up to 5,500 degrees centigrade.
Inner Core: This layer is believed to be solid, because of the immense pressure
placed upon it. It contains the centre of the earth which is about 6,378km from the
surface. It is also extremely hot at about 5,500 degrees centigrade.
Continental crust is also known as sial and is less dense than sima.
3 billion years old, composed of granite, 20-80 km thick
Continental crust is discontinuous through oceans
Continental crust is older
Continental crust is normally thicker
Continental crust is less dense (lighter)
Continental crust can't be made
Continental crust can't be destroyed.
Oceanic crust is known as sima and is denser than sial.
70-100 million years old, composed of Basalt, 10 km thick
Oceanic crust is continuous
Oceanic crust is younger
Oceanic crust is normally thinner
Oceanic crust is denser (heavier)
Oceanic crust can be destroyed
Oceanic crust can be made
Why Plates Move
Plates at our planet's surface move because
of the intense heat in the Earth's core that
causes molten rock in the mantle layer to
move. It moves in a pattern called a
convection cell that forms when warm
material rises, cools, and eventually sink

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down. As the cooled material sinks down, it is warmed and rises again.
Scientists once thought that Earth's plates just surfed on top of the mantle's
giant convection cells, but now scientists believe that plates help themselves
move instead of just surfing along. Just like convection cells, plates have
warmer, thinner parts that are more likely to rise, and colder, denser parts that
are more likely to sink.
New parts of a plate rise because they are warm and the plate is thin.…read more

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The plate tectonics theory dates back to the early 1600s. It is a scientific
theory which describes the large scale motions of Earth's lithosphere. The theory
has developed over time from the questioned theories of continental drift to
form the plate tectonics theory, more widely accepted by the scientific
community, with observations of sea floor spreading in the late 1950s and early
1960s.…read more

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Volcanic & Seismic events are pieces of evidence proving that the plate
tectonics theory is valid
describe the distribution of volcanoes around areas such as the Pacific
ring of fire and explained how without movement at the boundaries
around the Pacific, volcanoes such as Mt St Helens and Pinatubo would
not simply not be volcanoes, as they would have no 'fuel' caused by
the subduction of an oceanic plate under a continental plate.…read more

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causing shockwaves to rip through the surrounding area, an example
of this is the 1995 earthquake in Kobe, Japan where the plate
slipped over 1m. Earthquakes are also common however at
conservative margins, where plates slip past each other and the build
up of friction can cause seismic activity regularly. The San Andreas
fault for example in California is a conservative margin and the
fault lines show where the crust has failed, the slippages of plates here
caused the 1989 San Francisco earthquake.…read more

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Wegener ­ The Origins of Continents and the Oceans
Alfred Wegener was the scientist who championed the Continental Drift Theory
through the first few decades of the twentieth century. Simply put, his
hypothesis proposed that the continents had once been joined, and over time
had drifted apart. The jigsaw fit that the continents make with each other can be
seen by looking at any world map.
Wegener did not even present Continental Drift as a proven theory.…read more

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o "If we are to believe in Wegener's hypothesis we must
forget everything which has been learned in the past 70
years and start all over again." He was right.
After Alfred Wegener died, the Continental Drift Theory was
quietly swept under the rug. With the Continental Drift Theory
out of the way, the existing theories of continent formation were
able to survive, with little challenge until the 1960's.…read more

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(normal) polarity. 3. Stripes of rock parallel to the ridge crest
alternated in magnetic polarity (normal, reversed, normal. Etc.),
suggesting that the magnetic striping and the construction of the
id-oceanic ridge system, the sea floor spreading hypothesis gained
converts and represented another major piece of evidence towards
the theory of plate tectonics
Henry Hess is best known for his theories on sea floor spreading,
suggesting that the convection of the Earth's mantle was the
driving force behind this process.…read more

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Tectonic plates are powered by convection currents, which is the
circular movement of magma within the mantle. These currents are
powered by the core, which heats the magma, causing it to rise, cool
and fall back down. This circular motion causes the plates, which float
on the mantle, to move.
The entire outer surface of the planet is divided into these plate
formations, roughly 30 in total The Pacific Plate to the Galapagos micro
plate at 12,000 square miles.…read more

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plate margins, shallow focus earthquakes occur over a broad zone, for
example Sichuan, China 2008.
Different materials transmit and reflect seismic shock waves in different
ways, and of particular importance to the theory of plate tectonics is
the fact that liquid does not transmit S-wave. Because the mantle
transmits S-waves, it was long thought to be a cooling solid mass.
Geologists later discovered that radioactive decay provided a
heat source within Earth's interior that made the asthenosphere
plasticine (semi-solid).…read more


tom dixon

This is really good thank you!


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