Convection and the Mantle How is heat transferred?

What makes an object hot? Movement of particles Heat moves toward colder areas

3 Types of Heat Transfer Radiation Conduction Convection

Radiation Transfer of energy through space No direct contact between heat source and an object. Can you think of examples of Radiation? Sunlight warming us during the day Being warmed by a fire

Conduction Heat transfer within a material, or between materials that are touching. The particles heat up, move faster, and bump into other particles that do the same.

Conduction: Examples A spoon sitting in a boiling pot of soup. Hot sand at the beach. Cold hands after making a snow ball.

Convection Heat is transferred by the movement of fluids and gases. Heated particles begin to flow, and transfer heat from one particle to another. This is caused by differences in temperature and density* in a fluid. Density = a measure of how much mass there is in a substance. Example: Rock is much denser than water.

Convection Currents How does hot liquid move? Think of the boiling pot of soup: The soup on the very bottom of the pot is the hottest, and therefore, less dense. It begins to float towards the top. Once at the top, it cools, which increases its density. It becomes heavier, and due to gravity, falls back to the bottom of the pot.

Convection currents take on a circular motion. This is how the mantle rock moves inside the earth.

Changes in Density The heating and cooling of a fluid changes its density. What a fluid is heated, it’s particles move farther apart at a faster speed than when it was cold. As the particles spread out they take up more space. The particles of the fluid are now being stretched over a larger area, and therefore, the density of the fluid decreases.

Inside the Earth Heating and cooling of a fluid, changes in the fluid’s density, and the force of gravity combine to set convection currents in motion. Heat from the core and mantle causes these types of convection currents in the mantle.

The flowing mantle Plumes of mantle rock rise slowly from the bottom of the mantle toward the top. The hot rock eventually cools, and sinks back through the mantle. This cycle of rising and sinking is repeated over and over. This has been happening inside our earth for more than 4 billion years!

Convection Currents in Action: http://duedall.fit.edu/wholeearth/PHysical%20geology%20animations/0053.swf