Only a small fraction of the energy released by the sun reaches the Earth’s atmosphere. The spectrum (range) of solar radiation is shown in the following figure. Visible light forms only a small part of the entire spectrum. Incoming solar radiation is selectively absorbed and reflected to warm the Earth and atmosphere and to maintain a temperature friendly to life.

meteorite Mass of stone or metal that has passed through the atmosphere and has struck the Earth’s surface.

meteoroid Mass of stone or metal traveling through space.

photosynthesis Process by which plants use chlorophyll and energy from sunlight to manufacture food from carbon dioxide.

pollution Waste substances added to the environment.

respiration The process by which oxygen combines with food to release energy and carbon dioxide.

scattering The bending of light rays in all directions by gas molecules.

spectrum A broad range of related waves.

Incoming radiation. Our atmosphere and clouds reflect about 40 percent of the incoming solar radiation back out into space. The remaining 60 percent is responsible for warming the Earth and atmosphere. About 20 percent of the total incoming radiation is absorbed directly by the atmosphere. The ozonosphere and ionosphere are responsible for most of this absorption of radiation. The remaining 40 percent of the total solar radiation reaches the surface of the Earth. As the solar radiation penetrates the lower layers where air is dense, some scattering occurs. Scattering is the bending of light rays in all directions by gas molecules. Some light rays are lost back to space. Since blue light is most affected by scattering, the sky appears blue.

Energy released by a very hot object like the sun is in the form of short-wave radiation. Land and water can absorb this form of radiation far better than can the atmosphere. As a result, the Earth’s surface is warmed. Since the Earth is a warm object, it too releases energy. Ground radiation is of the long-wave form because the Earth emits longer, infrared radiation. Figure 5 above shows the abrupt change of the incoming solar radiation to longer wave length heat when the sunlight strikes the ground. Figure 6 indicates that about one half of the sun’s energy is available to heat the surface of the Earth.

Greenhouse effect. Long-wave radiation given off by the warm Earth is absorbed by water vapor, clouds, and carbon dioxide in the atmosphere. The trapping of ground radiation (heat) by the Earth’s atmosphere is called the greenhouse effect. In a greenhouse, glass takes the place of the water vapor and carbon dioxide. The sun’s short-wave rays pass through the glass roof, but the glass will not permit the long waves to escape. As an example of the atmosphere’s greenhouse effect, the temperature does not drop as much on a cloudy night as it does on a clear night.

Radiation balance. Scientists have made many measurements of the radiation reaching the Earth’s surface. The exact amount of heat absorbed by the atmosphere and the Earth varies from place to place and from time to time. The data gathered over many years shows that the Earth as a whole is neither gaining nor losing heat. This means that the amount of radiation absorbed by the Earth and the amount of heat lost to space are equal. If the energy balance were not equal, the Earth would either become extremely hot like the inner planets or would cool off to frigid temperatures like the outer planets. Do you think that all the numerous factors producing an energy balance which are favorable to sustaining life have occurred by random accident, or by creative design? Loss of heat energy is greater at night than during the day. At the equator, more energy is gained than lost. In contrast, at the poles, more energy is lost than gained. Therefore, excess heat generated at the equatorial regions is transferred to the poles by global air circulation patterns.

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INFLUENCES ON LIFE

God created an atmosphere exactly suited for many forms of life. Our atmosphere is necessary to sustain life. The qualities of our atmosphere cannot be appreciated until changes take place that threaten life. The atmosphere plays a vital role in the processes of respiration and photosynthesis, in regulating temperature, and in protecting us from radiation and meteorites.

Respiration. All living things need energy to stay alive. Energy is obtained from food when it is combined chemically with oxygen. The oxygen necessary for this process is readily available in the atmosphere. A process in which living things obtain energy from food is called respiration. The waste products that result are carbon dioxide and water. Respiration can be represented by the following word equation:

Photosynthesis. Although carbon dioxide is a waste product of respiration, plants use it to make food. Plants take in carbon dioxide through their leaves and water through their roots. With the help of sunlight and a green substance called chlorophyll, plants convert carbon dioxide and water into food. This process by which plants make food is called photosynthesis. A by-product of photosynthesis is oxygen. Photosynthesis can be represented in this way:

Animal life is dependent upon plants for oxygen. Plants, in turn, need the carbon dioxide given off by animal life to produce food and oxygen. Both carbon dioxide and oxygen are available in the atmosphere.

Radiation. The atmosphere plays an important role in protecting the Earth from harmful radiation. Ultraviolet rays that penetrate the atmosphere cause the skin to be tanned. Exposure to ultraviolet rays for too long can cause skin cancer. People who must work in the sun often have thin, wrinkled skin. The ozonosphere absorbs ultraviolet radiation. This protective shield is another evidence that God designed and created our universe–it was not produced by chance.

X-rays are more dangerous than ultraviolet rays. The amount of damage to the body is determined by the amount of exposure. Bone marrow, sex organs, digestive system, and blood vessels are some of the body parts affected most by radiation. Babies may be born with deformities if the mother is exposed to radiation. People who work with radiation might develop cancer. Very powerful forms of radiation or overexposure can ultimately cause death. The ionosphere absorbs all but a small amount of gamma radiation and X-ray radiation.

However small the amount of radiation, living things are affected in some way. Humans are usually exposed to only small amounts of radiation over their lifetime. This small amount may be responsible for shortening life.

The Bible provides man with a record of life spans for descendants of Adam and Eve. We can see that man lived to reach ages of about 900 years until Noah’s flood. After the flood, life spans dropped rapidly. This record, combined with other scientific evidence, appears to indicate that the pre-flood atmosphere provided more ideal temperatures worldwide. In addition, the chemical properties of the pre-flood atmosphere may have been somewhat different from our present atmosphere. It also appears that this atmosphere provided greater shielding from harmful solar radiation.

Temperature. The amount of atmosphere a planet possesses has a great effect on temperature range. The moon has no detectable atmosphere. Temperatures on the moon reach just above the boiling point of water on the side facing the sun. Mars, however, has a thin atmosphere. Temperatures near its equator range from 27°C (80°F) during the day to -70°C (-100°F) during the night. Although Mars receives less than half the energy that the moon receives, the temperatures on Mars are far less extreme. Any amount of atmosphere around a planet will moderate the temperature.

For life to exist the temperature range on Earth must be maintained within a narrow range. The current temperature balance is also linked directly to the water cycle which is presented in the following section. The water-ice-precipitation balance would be severely disturbed if the Earth’s average temperature rose or fell.

The world’s temperature is being maintained at an average of 15° C. This is caused by an exact balance between the incoming solar radiation and the heat given off by the Earth and its atmosphere to outer space. If the Earth radiated just slightly more energy to space than absorbed, it would slowly cool and eventually become a frozen lifeless mass. If the reverse condition occurred, all surface liquids would soon boil, leaving the Earth a barren desert, without life.

Meteoroids. Meteoroids are solid objects moving through space at very high speeds. These objects are made of metal or stone. Most are about the size of grains of sand, though some are as large as giant boulders.

Meteoroids that collide with the atmosphere are called meteors . They are heated by friction with air molecules. Usually at about 60 miles above the Earth (the lower thermosphere) they become white hot and burn up.

Large meteoroids that do not completely burn up may collide with the Earth. The part that reaches the Earth’s surface is called a meteorite. One meteorite that fell in a Kansas cornfield was estimated to weigh over one ton. At a few places on Earth, giant meteorites have blasted out large craters. Some craters are as large as several miles across. Meteorite craters have been found on nearly every continent.

Other than the occasional observance of meteoroids or “falling stars,” we are unaware of the protection our atmosphere gives. Scientists have estimated that over 25 million meteoroids enter the Earth’s atmosphere every day. Planets with little or no atmosphere give us a clue. Mars, Mercury, and numerous satellites of our solar system show the effects of continual bombardment by meteorites. The surfaces of these planets are pitted with craters. Although most meteorites are very small, the power they possess is many times that of a bullet fired from a rifle. Safety is possible only with a thick, protective atmosphere.

It is interesting to note that meteorites are only found on the Earth’s surface or in rocks just below the surface due to surface impact. Think about this–if the rocks covering the Earth accumulated slowly over millions of years, wouldn’t you expect meteorites to have been found in deep rock layers, just like we find them at the surface?

CHANGES

Man’s knowledge of the atmosphere is continually growing. Many changes occurring in the atmosphere go unnoticed with single measurements. Information gathered over many years reveals that small changes are taking place. The total amount of carbon dioxide in the atmosphere is estimated to have increased by 10 to 15 percent since 1900. This is probably caused by the increased burning of fossil fuels such as coal, petroleum, and natural gas. Another source of additional carbon dioxide is volcanoes and hot springs. Volcanoes and hot springs also produce large quantities of water vapor.

Activities of man seem to be causing some harm to our atmosphere. Pollution is very much a concern today. The full extent of the effect to the atmosphere is still unknown. Larger amounts of carbon dioxide in the atmosphere may cause a warming trend. Air pollution reflects radiation and could cause a cooling trend. Scientists have not come to an agreement on the long-term effect of pollution on the atmosphere. Air pollution may have greater effect on health than on the atmospheric temperature.