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Our Changing Atmosphere
The atmosphere of the
early Earth would have been unable to support life, due to its lack of
oxygen. In addition, it would have been toxic to us. It had a large
component of volcanic gases in it, including a huge amount of carbon
dioxide, as well as carbon monoxide, methane, sulfur dioxide,
hydrogen, water vapor, and many others. About the time plants expanded
their territories onto land, and became much more common on both land
and sea, the carbon dioxide levels began to drop and oxygen levels to
rise simultaneously, until they reached the levels they are today. Our
modern atmosphere, which has been 78% nitrogen, 21% oxygen, and only a
trace of water vapor, CO2, and other gases for some time now, is still
undergoing gradual change, largely due to human activity. As a
consequence of our industrialized societies and our consumption of
massive quantities of fossil fuels, we have more than a trace of water
vapor and CO2 in our atmosphere now, as well as CO, lead, and
particulate matter (ash, soot, and cinders, in spite of our attempts
to “scrub” the exhaust of our coal burners before releasing it into
the world,) and they are steadily growing. These gases contribute to
the Greenhouse Effect, as does the ozone we have released down here in
our troposphere. (The ozone up in our stratosphere does not contribute
to global warming, but it does protect us from ultraviolet radiation.)
We have passed more laws to clean up the air, including banning
chlorofluorocarbons (CFC’s) from aerosol cans, to prevent the further
destruction of the ozone layer in the stratosphere, and laws requiring
that the freon used in air conditioning and refrigeration systems to
be kept “closed,” and not released into the atmosphere. Unfortunately
the liberal use of styrofoam, whose production is devastating to air
quality, and the use of halons in firefighting are just two of the
many more ways we still pollute the sir with seemingly little regard
for the future.
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SAMPLE QUESTION |
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1. |
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According to this graph, during which year
was the earth’s temperature right about its average (its
“long term mean”)? |
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A. |
1890 |
C. |
1945 |
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B. |
1915 |
D. |
2000 |
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2. |
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During which 2 years was it well above average? |
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A. |
1890 |
C. |
1945 |
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B. |
1915 |
D. |
2000 |
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3. |
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What might account for it being so high those two
years? |
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