A lot of energy goes into the bottom of the energy pyramid, and only a little is left at the top. What happens to it? Where does it go?
The First Law of Thermodynamics
This law says that energy changes form, but it cannot be created or destroyed.
For example, our planet receives solar radiation. This energy comes to us as electromagnetic radiation.
As the radiation comes down through the atmosphere, some of the energy is reflected by the earth's albedo and some is absorbed and scattered by the atmospheric molecules. It gets changed into heat, which warms the atmosphere and is eventually radiated back out into space. The remaining radiation goes on down and reaches the surface of our planet.
At the planet's surface, much of the sun's radiation falls onto earth, rocks, and water. It is absorbed and some of it is reradiated as heat. I am sure that you have felt rocks and pavements warmed by the sun, and that there have been times when the rays of the sun have warmed you directly! Energy is also used to evaporate water and cause wind by warming air.
When electromagnetic radiation falls on a leaf, some of it, especially the green light, just bounces off. However, the leaf absorbs some of the energy during photosynthesis, changing the electromagnetic radiation into chemical energy. Again, some of the energy is lost as heat.
Chemical energy is used to form the tissues of the plant and for metabolism (life processes). Some of this energy is lost as heat. Some of this chemical energy is also stored as starch (a carbohydrate) in bulbs and tubers for later use.
When animals eat plants, they use some of the chemical energy stored in the plant tissues. Chemical changes provide fuel for metabolism, cell division, movement (chemical energy is transformed into mechanical energy) and even electrical energy in animal and human nervous systems. Again, energy is lost as heat. When animals eat animals, energy use is the same. With every use of energy, some energy is lost as heat.
Energy is stored in the bodies of animals and in plant tissues. This energy is released when organic material is burned. Burning is really very fast oxidation (a chemical change), and we see fire because so much heat is being given off by the change. Fossil fuels are stored chemical energy in ancient plant tissues.
Chemical energy can also be changed into mechanical energy, which is what is happening when we turn on the engines of planes and cars. Car engines get hot because heat is, again, a by product of energy change.
As you can see from the diagram, using energy or changing its form results in a loss of some of it to heat. This heat is released into the atmosphere and radiated out into space. Without the constant input of energy from the sun, our planet would soon be very cold. The temperature of the earth is a balance between the heat received and the heat radiated out of the atmosphere.
The Second Law of Thermodynamics
The second law of thermodynamics says that energy always changes from a more concentrated, more useful form to a less concentrated, less useful form.
Some energy is potential energy. Potential energy is energy that is stored in some way and not causing anything to change. An example would be a ball balanced the top of a flight of stairs: a tiny nudge could start it bouncing down. It has the potential to
Some energy is kinetic energy. This is the energy of a speeding car, an approaching asteroid, or a pendulum.