CONVECTION CURRENTS AND THE MANTLE

Heat Transfer

Earth’s molten outer core is nearly as hot as the surface of the sun.

Heat from the core of the Earth affects the mantle of the Earth.

The movement of energy from a warmer object to a cooler object is called heat transfer.

Heat is always transferred from a warmer substance to a cooler substance.

There are three types of heat transfer:

1. Radiation2. Conduction3. Convection

Radiation

The transfer of energy through empty space is called radiation.

Heat transfer by radiation takes place with no direct contact between a heat source and an object.

Radiation enables sunlight to warm Earth’s surface and the warmth you feel from an open fire or flame.

Conduction

Heat transfer by direct contact of particles of matter is called conduction.

Think about what happens when a metal spoon is left in a pot of boiling soup.

Heat is transferred from the hot soup and the pot to the particles that make up the spoon.

The particles near the bottom of the spoon vibrate faster as they are heated and bump into other particles heating them up as well.

Eventually the entire spoon heats up. When your hand touches the spoon,

conduction transfers heat from the spoon to your hand.

Convection

Heat transfer involving the movement of fluids (liquids and gases) is called convection.

Convection is heat transfer by the movement of a heated fluid.

During convection, heated particles of fluid begin to flow, transferring heat energy from one part of the fluid to another.

Heat transfer by convection is caused by differences of temperature and density within a fluid.

Density is the measure of how much mass there is in a volume of a substance.

When a liquid or a gas is heated, the particles move faster.

As the particles move faster, they spread apart and take up more space causing the density to decrease.

As a fluid cools, its particles move more slowly and settle together more closely causing the density to increase.

See Figure 9 on Page 26

A constant flow begins as the cooler substance continually sinks to the bottom and the wamer substance rises to the top.

A convection current is the flow that transfers heat within a fluid.

The heating and cooling of the fluid, the changes in the fluid’s density and the force of gravity combine to set convection currents in motion.

Convection currents continue as long as heat is added and will stop when heat is stopped and all of the materials have reached the same temperature.

Convection in Earth’s Mantle

Just like soup in a pot on the stove, Earth’s mantle responds to heat.

The heat source for the currents in Earth’s mantle is heat from Earth’s core and from the mantle itself.

Hot columns of mantle material rise slowly through the asthenosphere as it is heated.

At the top of the asthenosphere, the hot material spreads out and pushes the cooler material out of the way.

This cooler material sinks back into the asthenosphere where is heated again and the cycle is repeated.