Energy is not created nor destroyed. I am sure you have heard that plenty of times. What does it mean? We talk about using energy……if energy is used up, then how can we say that it is not destroyed?

The secret to understanding energy use is to understand that energy is used but not used up! Do you understand the difference? Energy does not change in amount but it changes form very easily. When we use energy, we do not use it up. Instead we change its form. For example, consider the energy coming from the sun. It is radiant energy. When the sun’s energy hits the desert soil in southern Utah it changes form to become heat energy. The amount of energy does not change but the type of energy changes.


The heat energy of the desert warms the surrounding air. The warm air rises which causes wind. Some of the energy dissipates out to space in the form of heat (it does NOT return to the sun) and some of the energy changes form to become energy of motion as the wind blows.

The electrical energy may be used in a light bulb, in which case it is changed to light energy.

Remember that energy flows from the sun, through the various Earth systems and eventually flows to space in the form of heat. When heat energy flows to space, it is lost to us. The energy is still there but it is not in a form that is useful to us. Because it is not useful to us, I call it lost. In reality, it is not lost. It is still there but it may as well be lost to us because we cannot use it again.


Radiation is the movement of energy in rays. The sun’s energy comes to Earth in the form of radiation. . So, how much radiation energy do we get from the sun? Every day, more energy falls on the U.S. than we use in an entire year. The total amount of solar energy per year falling on the continental 48 states is 1.37 * 1016 kW-h/year - or 46,700 ?/year - of solar energy. Compare this to 94.2 Quad/year, the rate of energy consumption in the 1997 ( Ref: Renewable Energy Annual 1998, DOE/IEA-0603(98), pg 1.) Every day more solar energy falls to the Earth than the total amount of energy the planet's 5.9 billion inhabitants would consume in 27 years (.) . That is a lot of energy! What happens to that energy?

About 30% of the sun’s energy is reflected or bounced back, immediately to outer space in the form of light. It never makes it to Earth. Clouds reflect back about 25% of the sun’s energy and snow, ice, and other reflective ground surfaces send back an additional 5%.

So, how much of the sunlight that comes toward Earth actually makes it to Earth? Do the math. Take the 30% that is reflected back and subtract it from the original 100% and you get……..70%. Good job. The remaining 70% of the sunlight that reaches Earth is absorbed, or taken in. This absorption occurs in many ways. The atmosphere absorbs twenty-five percent (25%). Forty-five percent (45 %) is absorbed by the Earth’s surfaces. Of that 45%, about 16% is immediately re-radiated as heat, 24% evaporates water, and 5% powers our winds.

Most of the sunlight that reaches the Earth is absorbed by water and solid materials and immediately converted to heat. Think of asphalt in the late afternoon of a sunny day. It has definitely absorbed some of the sun’s energy. HOT!! Or remember the warmth of the sun’s rays on your back. The energy in the sunlight was changed to heat energy which warmed you. Any material that is heated by the sun will then radiate that heat outwards. You do it, the asphalt does it, everything that is heated by the sun eventually loses that heat as it radiates back out. Eventually that heat radiates through the atmosphere and leaves the Earth to become “lost in space”.

A large amount of the solar energy that arrives on Earth powers the water cycle.

Plants capture a tiny but very important amount of the sun’s energy, about 0.08%.

There you have it. Energy is never created or destroyed. It does not increase or decrease in amount. It does, however, change from one form to another. Energy flows through the Earth’s systems. It changes form but it does NOT recycle. The solar energy absorbed by Earth eventually changes to heat energy that is “lost in space”.

Through the process called photosynthesis, plants convert the sun’s energy to chemical energy. The energy is stored in the chemical bonds of the sugars formed in plants. Those of us who eat plants change the chemical energy in the food to body heat. We lose body heat all the time. Guess where that heat goes? Eventually it leaves the atmosphere and is “lost in space.”


Water absorbs the sun’s energy and evaporates to become a gas in the atmosphere. When the water vapor condenses back into a liquid (rain) or solid (snow, sleet), the same amount of energy that was absorbed to evaporate the water is released as it condenses. The energy is released as heat that escapes the atmosphere and is “lost in space”.

> Or it may be used in a toaster, in which case it may be changed to heat energy. In all cases, the energy is not destroyed. It simply changes form. Eventually, the energy we receive from the sun is changed to heat energy and is lost to space.


We could go even further and pretend that the wind energy moves the blades of a windmill where there is a generator. The generator changes the wind’s energy of motion to electricity, another form of energy. Notice that in all of these steps, energy is not destroyed. It changes from one form to another but it is not destroyed or used up.


There are TWO parts to this assignment. You must do BOTH parts to receive credit for the assignment.

1. Create a diagram that illustrates the distribution of energy coming from the sun that is reflected, changed to heat, or stored in plants. Use the data in the preceding paragraphs to create your diagram.

· You may use whatever medium is best for you to create your diagram.

· You can create a diagram on your computer and email it to me.

· You can draw a diagram, scan it, and email it to me.

· You can create a poster or drawing and send it to me via regular mail. (My address is on the INFORMATION page for Earth Systems.)

2. Describe the pathway for converting radiant energy from the sun to the chemical energy that is stored in gasoline and used to transport you to school (or on a date or to a concert or wherever you want to go).

· Remember that gasoline comes from plant material that has been subjected to heat and pressure when it was buried deep in the Earth.

· Be sure to include the word photosynthesis in your description.

· All the information necessary to complete this assignment is available to you as you think about what is written in the paragraphs above and apply what you have learned to what you already know about energy pathways. You may submit your description in writing. Use proper punctuation, grammar, and spelling.

· Or you may submit your description as a diagram. If you create a diagram, you must label each energy conversion. (light to heat or light to chemical, etc…). Also, if you create a diagram, you may submit it to me in any of the forms mentioned in #1.

· The following website will help you understand the sun to gasoline process. ?


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