|Miles, Vaden W. College Physical Science. New York: Harper & Row, 1969.||"The atmosphere, or air, extends upward from the surface of land and water for perhaps 600 miles."||965 km|
|Lide, David R. Handbook of Chemistry and Physics. 77th Edition. New York: CRC, 1996.||"The Earth's atmosphere from the surface to 1000 km, as it is assumed to exist in a period of moderate solar activity."||1000 km|
|Gillmor, C. S. Twentieth Century Physics. Philadelphia: American Institute of Physics, 1995.||"The ionosphere, extending from about 50 to 1000 km above the Earth's surface."||1000 km|
|Gresswell, R. Kay. Physical Geography. New York: Praeger, 1967.||"Fig. 24. Layers of the atmosphere 300 miles"||482 km|
|Gwinn, Robert P. Encyclopedia Britannica. Chicago: Encyclopedia Britannica, 1986.||"The depth of this mantle of air may be some what arbitrarily placed at about 1000 km."||1000 km|
The Earth's atmosphere is made up of many gases, primarily nitrogen, oxygen, argon and carbon dioxide. The Earth's atmosphere consists of four layers. The first layer is the troposphere where the temperature decreases with increasing height. The next layer is the stratosphere, where the temperature remains approximately the same throughout. Above this layer is the mesosphere, where at first temperatutes increases with increasing height, but then again decreases. The last layer, the ionosphere, has increasing temperature with increasing height.
The thickness of the Earth's atmosphere is not a definite number, but is estimated to be about 1000 km. The reason that there is no definite number is because there is no set boundary where the atmosphere ends. As the altitude of air increases there is a decrease in atmospheric gases in the air, but there are still some traces of it. So it is difficult to pinpoint a definite boundary. The thickness of the atmosphere was found in five sources, one of which is not consistent with the rest. I decided that the value of 1000 km is about right.
The Physical Geography book showed that the thickness of the atmosphere was 480 km. I think the reason that this book's value was different from the four other sources is partly due to the fact that it was written so long ago (1967). The procedures and methods used to find the thickness of the atmosphere could have been different. Also the person who researched information for this book might have done little research on the thickness of the atmosphere and the related topics. The reason for my assumtion comes from the type of information found in this book.
Other regions of the atmosphere could also be identified according to parameters other than temperature gradient. The ionosphere is a region characterized by the presence of large numbers of ions (quoted information from the Encyclopedia). This shows that the other books had more information about the atmosphere and thus I think that the other books were more accurate in determining the measurement.
Andrea Park -- 1997[an error occurred while processing this directive]