Chapter 1 Section 2:
Convection Currents and the Mantle
Remember from Section 1:
•The Earth’s molten outer core is
nearly as hot as the surface of the
sun.
•This heat affects the mantle
through heat transfer: The
movement of energy from a warmer
object to a cooler object.
Remember from Section 1:
•Heat is always transferred from a
warmer substance to a cooler.
Example: holding an ice cube.
•3 types of heat transfer: radiation,
conduction and convection.
Radiation, pg. 25
•Radiation is the transfer of energy
through empty space.
•Sunlight is radiation that warms Earth’s
surface.
•It takes place with no direct contact
between a heat source and an object.
•Other examples: Heat from a light bulb,
heat from an open fire.
Conduction, pg. 26
•Conduction: The heat transfer by direct
contact of particles of matter
•Examples: Pot of water on the stove,
thermometer.
Convection, pg. 26
•Convection is heat transfer by the
movement of a heated fluid (liquid or gas)
•Heated particles of fluid begin to flow,
transferring heat energy from one part
of the fluid to another.
•Convection occurs between differences
in temperature and density within a fluid.
•Remember: Density is the amount of
mass in a volume of a substance.
How Does Convection Work?
•As a liquid/gas heats up, particles move
faster and spread apart and occupy more
space. Density decreases
•As a fluid cools, particles move slower
and settle closer together and density
increases.
How Does Convection Work?
•Warm/less dense fluid moves upward and
floats over the cooler, denser fluid.
**Think of the air– where do we find
warm/cold air?**
•As it spreads out and cools it becomes
denser and gravity pulls it back down
where it is heated again.
How Does Convection Work?
•There is a constant flow where the
cooler liquid/gas continuously sinks to the
bottom as the warmer fluids rise.
Convection
•A convection current is the flow that
transfers heat within a fluid.
•This continues as long as heat is added.
•Without heat, convection currents will
stop as all material reaches the same
temperature.
Convection in Earth’s Mantle, Pg. 27
•Earth’s mantle responds to heat. The
heat source is the Earth’s core and the
mantle itself.
•Hot columns of mantle material rise
slowly through the asthenosphere.
Convection in Earth’s Mantle, Pg. 27
•At the top of the asthenosphere, the hot
material spreads out and pushes cooler
material back towards the lower
asthenosphere.
•This cycle of rising and sinking has
occurred inside the Earth for more than
4 Billion years!
Journal
• Describe what it’s like to be water that is
being boiled.
– Where are you moving fast or slow
– Are your particles close together or further
apart (where does that happen)
– How much space are you taking up.
– When are you less dense or more dense and
what happens? (Sink or rise)
– Relate this idea to how convection is
occurring in the mantle (asthenoshere)