1. The Cycling of Energy
Key Concept: Various Heat-exchange systems work in the Earth system and affect phenomena on Earth’s surface.

2. 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.

3. 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.

4. 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.

5. 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.

6. 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.

7. 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.

8. 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.

9. 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.

10. 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.

11. 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.

12. In the ocean, convection causes deep currents.
Deep currents are streamlike movements of water far below the ocean surface.
Deep currents take more than a thousand years to travel around the entire ocean.

13. Convection currents in the atmosphere form when cold air sinks and forces warm air away from Earth’s surface.

14. 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.

15. 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.

16. 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.

17. 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.

18. 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.

19. 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.

20. 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.