What drives plate movement?
Understanding the movement and behavior of the Earth's outermost layers has been a painstakingly long
scientific process. The theory of plate tectonics is our current "best explanation" and working model for
answering these questions. Plate tectonic theory has developed slowly and progressively since it was developed
in the 1960s. It is a theory that truly has the entire world as its experiment.
According to the theory of plate tectonics, the Earth's crust and upper mantle are broken into moving plates of
"lithosphere." The lithospheric plates are solid rock. There are several very large plates, each consisting of both
oceanic and continental portions. There are a dozen or more smaller plates. The plates average about 80
kilometers (50 miles) in thickness.
All of the plates are moving. They are slow, moving at speeds of centimeters to tens of centimeters per year.
They slide along on top of an underlying mantle layer called the asthenosphere, which contains a little magma
(molten rock). Many types of evidence indicate that the
plates move.
Many lines of evidence indicate that the plates are moving.
What is less clear, however, is why the plates move. There
are two main scientific ideas for explaining plate
movement: gravity and convection
currents. All objects on and in the
Earth are pulled towards its center
by the force of gravity. This may
affect the plates at converging plate
boundaries in areas called
subduction zones, where one plate sinks into the mantle. Some evidence suggests that
gravity pulls the sinking plate down. The rest of the plate is dragged along behind it. This
is physically similar to slowly pushing a piece of paper off a table; it eventually bends,
and slides off, pulling the rest of the paper behind it. The other reason for plate motion relates to convection
currents within the upper part of the mantle. Convection is the heat-driven circulation of a fluid. In the mantle,
heat from deeper in the Earth causes the overlying mantle to circulate. The mantle can circulate because it
contains a little magma (molten rock); it behaves like a very hot mush. Mantle convection currents move very,
very, slowly. It is possible that as the mantle convects, it drags the overlying plates along with it. It is likely that
both convection and gravity contribute to the movement of the plates.
This unit introduces the importance of convection currents into the overall concept of plate tectonics.
Convection currents are common in everyday life. Water that is put over a hot stove heats by convection. The
water closest to the heat source becomes less dense and rises. The water that is cooler and on top will sink to
the bottom. This sinking of the denser fluid and rising of the less dense fluid causes movement in a circular
motion as shown in the diagram below; this is convection.
Article retrieved from: https://msnucleus.org/membership/html/k-6/pt/plate/2/ptpt2_1a.html
Thermal Convection
Scientists believe that one of the primary forces behind plate movement is thermal convection. Thermal
convection is when heat from the core of the Earth is transferred to the surface of the Earth by the mantle. The
mantle is the thick, mostly solid layer of the Earth between the crust and the core. Thermal convection works a
lot like a pot of boiling water.
In convection, heat from the stove warms up the water closest to the stove, causing the water to expand and
rise. Cooler water near the surface of the pot sinks to take the place of the rising water. In doing so, a current of
water is set up flowing toward the surface and back down again. Using this model, the stove is like the core and
the water is the liquid mantle that rotates. The plates on the Earth's surface would be floating on top of the
water. These currents push the plates along according to the direction of flow. Geologists think that this same
phenomenon is what is happening inside the Earth. Liquid rock near the mantle is heated and rises toward the
crust. The rock near the surface is cooler and sinks back down toward the core. This forms the same type of
convection current that causes the plates to move. Scientists believe that this cycle of magma rising from the
core to the crust and back again takes thousands of years to complete.
At the top of the mantle, the rock encounters the thin crust,
and, as it pushes it aside, lava flows out from the mantle to
form new oceanic crust. As this happens, the plates smash
into each other, slide past each other or are pushed under
another plate. This movement of the plate along with the
upwelling of the mantle by the convection currents may also
cause secondary actions that assist in plate movement.
http://study.com/academy/lesson/causes-of-tectonic-platemovement.html
Convection currents in the liquid mantle cause the plates to move
Convection Currents affect the weather all over the
Earth. Convection currents can affect even the
smallest amount of weather, like wind. An example
of this occurs when a land mass is adjacent to a body
of water. When a land mass is adjacent to a body of
water during the day it causes a sea breeze. A Sea
Breeze happens when the land heats up faster than
the water which means the air over the land is
warmer and less dense than the air over the water.
Since the air is less dense it rises, then the colder
more dense air from the water replaces it and
causes an onshore breeze.
http://convectioncurrentscienceproject.weebly.com
/weather.html
NAME(S): __________________________________________________________________
RECORD your examples/evidence of using your DISCOURSE NORMS when
discussing the article with your partner. Use complete sentences.
Paraphrase
(Use your own words to
restate the thoughts of your
partner.)
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Ask a Question to
clarify thinking
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Challenge their thinking
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Add to their thinking
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1. What are the inner layers of Earth?
CRUST
LITHOSPHERE
ASTHENOSPHERE
MANTLE
2. How are the plates moving? (What is causing them to move?)
3. What are convection currents?
4. What is thermal convection?
Fifth Period- Main Ideas
1. What are the layers of Earth?
2. What causes plates to move?
3. What is the theory of plate tectonics?
4. What is convection/thermal convection?
Sixth Period
1. What causes plate movement?
2. What are the layers of Earth?
3. What is convection/thermal convection
(currents)?
Seventh Period
1. What are the layers of Earth?
2. How are the plates moving?
3. What is thermal convection?
4. What are convection currents?