Transcript DYNAMIC PLANET I

DYNAMIC PLANET
INVESTIGATION 3 NOTES
CONVECTION CELLS
• Definition – a motion in a fluid that is
caused by heating from below and cooling
from above
Examples
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Heating of the corn syrup demonstration
Oatmeal demonstration
Home heating systems
Convection oven
Convection Cells
• When a fluid is heated, it expands and
lowers its density slightly
• The expanded fluid (less dense) rises 
reaches cooler surroundings  shrinks,
becoming more dense  sinks heated
again…
Forms CONVECTION CELLS
Convection of the Earth’s Mantle
• The mantle convects in the form of
gigantic convection cells
Material movement
• Many materials act like solids on short
time scales but like liquids on much longer
time scales
– Examples include:
• Silly Putty
• Glass
• Wax
• These materials flow and take on a new
shape, even though it seems like a solid
• The Earth’s mantle behaves in the same
way
• The speeds of flow in the mantle are only
a few centimeters per year OR as fast as
your fingernail grows
The Lithosphere and
Asthenosphere
The Lithosphere
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Outermost part of the Earth
Cooler temperature
Remains rigid
Does not convect
Made up of the crust & uppermost part of
the mantle
• Consists of several pieces called
lithospheric plates
The Asthenosphere
• Below the lithosphere
• Zone where mantle rocks are just hot
enough & under enough pressure to
deform & change shape
• Able to convect  moving the lithosphere
Mid-Ocean Ridges
• All the Earth’s oceans have a continuous
mountain range, called a mid-ocean ridge
• Located above rising currents in the
mantle convection cells
• Stand high because they are heated by
hot rising material which expands the
rocks
• As hot mantle rock rises, some melts
forming magma
• Magma is less dense than surrounding
rock, rises to form volcanoes along the
ridge
• As rock rises, temperature stays the same
but pressure decreases (less weight of
rock above)
• Melting temperature decreases as
pressure decreases, why some rising rock
forms magma
• Magma reaches surface, solidifies to form
basalt
New crust is formed, moves away
from the crest of the ridge
• Due to movement of the mantle
• Due to downhill slope of the ridge away
from the crest
• Movement of new oceanic crust in both
directions  sea floor spreading