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The Cycling of Energy Key Concept: Various Heat-exchange systems work in the Earth’s system and affect phenomena on Earth’s surface. What You Will Learn • Heat flow is the transfer of energy from a warmer object to a cooler object. • Energy from the sun, the major source of energy for phenomena on Earth’s surface, is transmitted to Earth by radiation. • Heat from Earth’s interior reaches the surface mostly by convection. The Flow of Energy • Energy can be carried from one place to another by heat flow, waves, or by moving objects. • Heat flow is the transfer of energy from a warmer object to a cooler object. • Waves—such as water wave, light waves, and sound waves—transfer energy through vibrations. • Waves move energy, but they do not move matter. • Objects carry energy while they are moving. • As they move, the objects pass energy to objects that they touch. • The sun is the major source of energy for the Earth system. • Heat from Earth’s interior supplies a much smaller amount of energy. • Energy moves through the processes of radiation, convection, and conduction. Radiation • All energy from the sun travels to Earth in waves called electromagnetic radiation. • Electromagnetic radiation contains a wide range of wavelengths, collectively referred to as the electromagnetic spectrum. • Radio waves have the longest wavelengths, gamma rays have the shortest wavelengths. • All energy that Earth receives from the sun travels through space as electromagnetic radiation. • Wavelengths in or close to the visible light range make up most of the energy given off by the sun. • Some of this energy can pass through Earth’s atmosphere and reach Earth’s surface. • Energy from the sun drives the water cycle and makes life possible on Earth. • Energy from the sun is absorbed by Earth’s systems. • This energy is then converted to thermal energy and transferred by convection and conduction. Convection • Most energy is moved through Earth’s systems by convection. • Most convection occurs in fluids, such as water and air. • Some convection can occur in solids that flow like putty. • The uneven heating of matter drives convection. • Matter that is heated becomes less dense and rises. Cooler, denser matter sinks. • The movement of matter that results from difference in density is called a convection current. • In the ocean, differences in temperature and salinity cause differences in density. • Salinity is the amount of salt in salt water. • Cold, salty water has a higher density than warm, less-salty water. • In the ocean, convection causes deep currents. • Deep currents are stream like movements of water far below the ocean surface. • Deep currents take more than a thousand years to travel around the entire ocean. • Convection currents in the atmosphere form when cold air sinks and forces warm air away from Earth’s surface. Convection in the Geosphere • Convection also occurs in the geosphere. • Energy produced deep inside Earth heats rock in the mantle. • The heated rock is under high pressure, so it becomes plastic without melting. • The heated rock flows like putty. • As it becomes less dense, the heated rock rises toward Earth’s surface. • The cooler, denser rock surrounding the heated rock sinks. • In this way, heat inside Earth moves toward the cooler crust. • This movement of rock is a convection current. • Convection currents in the mantle cause the movement of tectonic plates. Conduction • When objects at different temperatures touch, their particles interact with each other. • Fast-moving particles in the warmer object transfer energy to slower moving particles in the cooler substance. • This causes the particles in the cooler substance to move faster and get warmer. • Energy can be transferred between the geosphere and the atmosphere by conduction. • When Earth’s surface is warmer than the atmosphere, the ground will transfer energy to the atmosphere. • When air comes into direct contact with the Earth, that energy is transferred by conduction. Earth’s Energy Budget • Energy on Earth moves through and between four spheres. • These four spheres are open systems, which means they constantly exchange energy with each other. • Energy is neither created nor destroyed. • It is simply transferred between spheres and converted into another form of energy. • You can think of this movement of energy as part of an energy budget. • An addition of energy in one sphere means a subtraction of energy in another.