GED Science Practice Test: The Atmosphere Close to Earth

As previously mentioned, the air pressure and water vapor in the troposphere make the air in this layer suitable for life.  There are other aspects of these layers that also contribute to sustaining life.

The Ozone Layer: One feature of the stratosphere that contributes to sustaining life on earth is the ozone layer, shown on the following diagram:

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The ozone layer has a high concentration of ozone molecules, which consist of three oxygen atoms bonded together.  Ozone has the chemical formula O3Ozone has the unique property of being able to absorb harmful ultraviolet radiation from the sun.  If we did not have the ozone layer, the incidence of skin cancers, cataracts, and some crop damage would increase.   Some human activity contributes to breaking down the ozone layer, and indeed, the thickness of the ozone layer over industrialized countries, like the United States, is thinner than in some other places.

The Greenhouse Effect: The greenhouse effect is a feature within the atmosphere, rather than a layer.  The greenhouse effect is what keeps us warm on earth.  Heat from the sun penetrates the earth’s atmosphere to reach the surface of the earth.  Then that heat can be reflected back from the surface of the earth (or the clouds in the troposphere).  If that reflected heat all left the earth’s atmosphere, earth’s temperature would not only be lower, but we would experience greater extremes in temperature between day and night.  To demonstrate this point, we need only look at Mars, which is a planet that does not have an atmosphere.  During the day, an average temperature for Mars could be 70F.  However, nighttime on Mars can drop to -100F.

The Greenhouse effect is necessary and good…up to a point.  However, if we have too much heat being trapped, catastrophic increases in temperature could result.  These catastrophic changes are referred to as global warming.  Humans pump more greenhouse gases, gases capable of trapping heat, into our atmosphere through transportation and other industrial processes.

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