# Lesson 3 Convection and Mantle

```Lesson 3
Convection and the Mantle
Vocabulary
• density-measure of how much
• convection-heat transferred
• convection current-the flow that
• conduction-heat transferred
• gravity-the force that pulls
energy that is carried in
rays like light
by the movement of fluids
between materials
mass there is in a given volume
of a substance
transfers heat within a fluid
objects toward each other and
toward Earth’s center
Introduction
Did you know that the solid rock in Earth’s
mantle can flow like a fluid? To learn this
concept look at a lava lamp. Heat from the
bulb causes solid globs of wax at the bottom
to expand. As they expand, the globs become
less dense and then rise through the more
dense fluid that surrounds them.
In Earth’s mantle, great heat and pressure
create regions of rock that are less dense
than the rock around them. Over millions of
years, the less dense rock slowly rises-like the
solid globs in the lava lamp.
How Is Heat Transferred?
• Heat is constantly transferred inside Earth and all around
Earth’s surface. For example, the warm sun heats the cooler
ground
• Heat always moves from a warmer object to a cooler object
• When an object is heated, the particles that make up the
object move faster, these faster-moving particles have more
energy
• The movement of energy from a warmer object to a cooler object is called
heat transfer
• There three types of heat transfer: radiation, conduction, and convection
• Radiation-the sun constantly transfers light and heat through the air,
warming your skin. The transfer of energy that is carried in rays like light
• Conduction-your feet can feel the warmth of hot sand, you will feel that
your feet are burning. The sand transfers its heat to your skin. Heat
transferred between materials that are touching is called conduction.
• Convection-the currents of warm air are created when warm air rises from
the ground, they will cool down as it rises to the air above that is cooler.
Heat transfer by the movement of a fluid is called convection.
Methods of Heat Transfer
Assess
• Work with a classmate to think of other examples of
heat transfer: conduction, convection, and radiation.
HINT: think about different ways to cook food.
format:
• Convection
• Conduction
How Does Convection Occur in Earth’s
Mantle?
• When you heat soup on a stove,
convection occurs in the soup
• The soup at the bottom of the pot
gets hot and expands
• As the soup expands, its density
decreases
• The warm, less dense soup above
the heat source moves upward and
floats over the cooler, denser soup
• Near the surface, the warm soup
cools, becoming denser
• Gravity then pulls the colder soup
back down to the bottom of the
pot
• Then, it is reheated and rises again
• A constant flow begins: cooler, denser soup sinks to the
bottom and at the same time, warmer, less dense soup rises
• The flow that transfers heat within a fluid is called
convection current
• Heating and cooling of a fluid, changes in the fluid’s density,
and the force of gravity combine to set convection currents
in motion
• Without heat, convection currents eventually stop
Video
Remember
• Remember that Earth’s mantle
and core are extremely hot
• Heat is transferred within
Earth by convection currents
• Remember that density is a
measure of how much mass
there is in a given volume of
a substance
• For example, most rock is
more dense than water
because a given volume of
rock has more mass than the
same volume of water
Apply It!
• Hot springs are common in Yellowstone Park.
Here, melted snow and rainwater seep to a depth
of 3,000 meters, where a shallow magma chamber
heats the rock of Earth’s crust. The rock heats
the water over 200C and keeps it under very high
pressure.
Compare and Contrast
• The heated water is more or less dense than
the melted snow and rainwater?
• What might cause convection currents in a hot
spring?
Convection Currents in Earth
• Inside Earth, heat from the core and the mantle act like
the stove that heats the pot of soup
• Large amounts of heat are transferred by convection
currents within the core and the mantle
• Heat from the core and the mantle itself causes
convection currents in the mantle
Convection
Currents
To understand
better, let’s take a
look at this figure
Temperature: colder
Density: more dense
The rock: sinks
Temperature: hotter
Density: less dense
The rock: rises
How is it possible for mantle rock to flow?
• Over millions of years, the great heat and pressure in the mantle
have caused solid mantle rock to warm and flow very slowly
• Many geologists think plumes of mantle rock rise slowly from he
bottom of the mantle toward the top
• The hot rock eventually cools and sinks back through the mantle
• Over and over, the cycle of rising and sinking takes place
• Convection currents like these have been moving inside Earth for
more than four billion years!
• There are also convection currents in the outer core. These
convection currents cause Earth’s magnetic field
Assess
• A convection current transfers _______ (heat/air/density)
within a fluid.
• In which part of Earth’s core do convection currents
occur?
• What would happen to the convection currents in the
mantle if Earth’s interior eventually cooled down? Why?
• Why is it colder near the floor than near the ceiling?
• How is heat transferred?
• What are the three types of heat transfer?
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What is gravity?
What effect does gravity have in convection currents?
What could cause rock to rise through Earth’s mantle?
Why might rock sink into Earth’s mantle?
How can solid rock flow?
Which Earth’s layers have convection currents?
Where is the hottest rock in the mantle?
Where is the coolest rock in the mantle?
How does the density of most substances change when the
substance is heated?
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