Suppose the solid dot to the right represents Earth. If I were to ask you to draw a circle around that black dot which would be the upper limit Earth's atmosphere called the troposphere (The part we breathe, fly airplanes in, and which contains over 90% of our oxygen), where would you draw it? When I do this in my earth science classes at the beginning of the year, I find some students who think our air extends all the way to the moon. I find other students who might draw the circle at what we have labeled A or B? or C and many who want to barely keep the circle on the paper. The fact of the matter is that, if you drew the circle accurately on the drawing, it would be so close to the dot you would he unable to see it as distinct from the dot. Earth's diameter is about 8,000 miles and the thickness of the atmosphere is much less than eight miles, making it 1/1,000th the diameter of Earth. Our air is like an onion skin around our planet.

You might wonder if the thin nature atmosphere is not a risk to us, but the fact of the matter is that our atmosphere is a uniquely designed structure and that, if it were any different than it is, would not allow life to exist. Think of all the things that allow us to live that are directly dependent upon the makeup of our atmosphere--a few are:

• The air has to be thin enough to allow enough light in for the photosynthetic processes of plants, but thick enough to burn up hunks of rock from space as they are pulled into the earth.
• The air has to be thick enough to provide oxygen to breathe, but not so thick as to create pressures that would cause oxygen toxemia.
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• The air has to be thick enough to trap enough of the sun's heat to keep us warm, but thin enough to not overheat us.
• The air has to be thick enough to refract and scatter dangerous radiation away from us, but thin enough to allow critical wavelengths to reach the earth for biological purposes.
• The air has to be thick enough to allow water to exist as a liquid, but not so thick that other gases liquefy or dissolve in water to kill all life.

These are just a sampling of the critical elements involved in the design of the troposphere, and there are many other layers above the troposphere that do other things that support life on this planet

Over the past 40 years, science has had the opportunity to examine the atmospheres of other planets within our solar system The comet strike on Jupiter in July, 1994, gave us a wealth of information about how the atmosphere is designed and what it does. We have seen Venus with our landers and probes and understand the acid in the air there and the greenhouse effect that has turned Venus into a hellish environment

Each day as the sun sets and we watch twilight come, we should he reminded of the incredible wisdom built into the way our atmosphere is structured. We do not have the ultraviolet light that bathes and sterilizes Mars because of our ozone layer which filters out that sunburning component of the light in the solar system. As the sky turns from blue to a brief green, to yellow, to orange, to red, we are seeing the longer wavelengths--which are never seen individually because they are mixed in our atmosphere. Our air keeps X-rays away from our planet. Its density allows flight and keeps the lakes and oceans from evaporating. Its low density allows it to move, carrying warmth and moisture from one area of our planet to another so that life can exist from the equator to the poles.

Earth's twilight is a constant reminder of the care and design built into our planet, but it also parallels how short life is. As an astronaut soars around the earth, watching multiple sunrises and sunsets, the beauty of the earth seems to never fall to bring comments of awe and appreciation. We need to appreciate the gift of life and the responsibility we have to make our lives count. Before your life enters its twilight, make it count. Use all God has given you to encourage, support, nurture, and uplift all to whom you have access.

                            John N. Clayton