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Convection and the mantle. After this lesson you will be able to describe how heat is transferred and explain how convection occurs in Earth’s mantle. Vocabulary . Radiation Convection Conduction Density Convection current. How is heat transferred?.
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Convection and the mantle After this lesson you will be able to describe how heat is transferred and explain how convection occurs in Earth’s mantle.
Vocabulary • Radiation • Convection • Conduction • Density • Convection current
How is heat transferred? • Heat is constantly being transferred inside Earth and all around Earth’s surface. For example, the warm sun heats the cooler ground. In fact, heat always moves from a warmer object to a cooler object. • When an object is heated, the particles that make up the objects move faster. The faster-moving particles have more energy. • The movement of energy from a warmer object to a cooler object is called heat transfer. There are three types of heat transfer: radiation, convection, and conduction.
Radiation, conduction and convection • The sun constantly transfers light and heat through the air, warming your skin. The transfer of energy that is carried in rays like light is called radiation. • Have you ever walked barefoot over hot sand? Your feet can feel as if they are burning! That is because the sand transfers its heat to your skin. Heat transfer between materials that are touching is called conduction. • Seagulls often soar on warm air currents. The currents are created as warm air rises from the ground. The warm air heats cooler air above it. Heat transfer by the movement of a fluid is called convection.
How does convection occur in Earth’s mantle? • Recall that Earth’s mantle and core are extremely hot. How is heat transferred within Earth? When you heat soup on a stove, convection occurs in the soup. That is, the soup at the bottom of the pot gets hot and expands. As the soup expands, its density decreases. • 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.
How does convection occur in Earth’s mantle? • A constant flow begins. Cooler, denser soup sinks to the bottom of the pot. At the same time, warmer, less dense soup rises. The flow that transfers heat within a fluid is called a 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.
Convection currents in Earth • Inside Earth, heat from the core and the mantle act like the stove that heats the pot of soup. That is, 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. 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.
Convection currents in Earth • Many geologists think 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. 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.
