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Unformatted text preview: This page last updated on 21-Apr-2011 EENS 1110 Physical Geology Tulane University Prof. Stephen A. Nelson Our Changing Planet We started this course by stating that the Earth is a complex system. Changes that take place in one part of the system have effects on other parts. The tectonic system is driven by the heat in the Earth. This drives the rock cycle, which is also affected by the atmosphere and biosphere. The atmosphere is in chemical equilibrium with the oceans and exchanges matter with the biosphere. All process act on a variety of time scales from hundreds of millions of years to microseconds. We as human beings are only now realizing that, as part of the biosphere, we have an effect on the Earth. What the effect is, we are only now beginning to understand. Here we try to put this in perspective. One of the reasons life exists on Earth is that the surface has a controlled temperature in the range between the freezing and boiling points of water. The Earth is the only planet in the solar system where this is true. Part of the reason for this results from the distance from the Sun. But, the reason that temperature remains fixed is controlled by the atmosphere. Solar Radiation and the Atmosphere Radiation reaching the Earth from the Sun is electromagnetic radiation. Electromagnetic radiation can be divided into different regions depending on wavelength. Note that visible light is the part of the electromagnetic spectrum to which human eyes are sensitive. The lowest wavelengths of the spectrum have the highest energy. Infrared & microwaves carry considerable amounts of heat energy. Earth receives all wavelengths of solar radiation. But certain gases and other contaminants in Global Change 4/21/2011 Page 1 of 10 the atmosphere have different effects on different wavelengths of radiation. Dry air is composed of about 78% Nitrogen, 21% oxygen, and 1% Argon. It also contains water, 4% at saturation, but saturation depends on temperature. In addition trace gases have an effect. Among the trace gases are: Ozone (O 3 ) Ozone is produced in the upper atmosphere (30 - 35 km above surface) by incoming ultraviolet radiation. Ultraviolet radiation causes O 2 to go to O + O. Some of the O then recombines with O 2 to make O 3 . This ozone then absorbs more ultraviolet radiation and breaks down to O 2 + O. This O can then can recombine with O 2 to make more Ozone. The process is self regulating and results in less ultraviolet radiation reaching the Earth's surface. Ultraviolet radiation is harmful to organisms because it is high energy radiation that damages cells. In humans, excessive exposure to ultraviolet light causes sunburns and skin cancer. Chlorofluorocarbons (CFCs) are produced to make refrigerants and styrofoam....
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This note was uploaded on 02/01/2012 for the course EENS 1110 taught by Professor Staff during the Fall '10 term at Tulane.
- Fall '10