Introduction
Each second the sun gives off an amount of energy equal to
200 billion hydrogen bombs (http://www.csi.ad.jp/ABOMB/data.html).
This energy reaches the earth in the form of electromagnetic
radiation. Electromagnetic radiation is energy that travels through
space in the form of waves. Very short wavelengths are gamma rays and
X-rays. Ultraviolet, visible light, and infrared are longer. The
longest are radio, television, and radar waves. Read more at:
http://imagine.gsfc.nasa.gov/docs/science/know_l1/emspectrum.html
The human eye sees a very small part of the electromagnetic spectrum
as visible light. Infrared waves are felt on the skin as heat.
Ultraviolet radiation can cause sunburn and tanning of the skin.
Prolonged exposure to ultraviolet radiation causes skin cancer,
blindness and a weakening of the immune system. Fortunately for all
living things on earth, not every kind of electromagnetic radiation
given off by the sun reaches the earth’s surface in large
amounts. The gases in the upper atmosphere absorb X-rays, gamma rays
and most of the ultraviolet rays. In the stratosphere ultraviolet
rays act upon oxygen molecules to form ozone. Ozone is one of the
gases in the stratosphere which has the ability to absorb ultraviolet
radiation. Ozone acts as a shield for the earth’s surface.
The Ozone Layer
In 1983 scientists observed that the amount of ozone in the upper
stratosphere was dropping at a dramatic rate especially over
Antarctica. At first scientists thought that this was the result of
increased sunspot activity, or the unusual weather system of the
Antarctic.
Today, scientists are convinced that the major culprit for the ozone
depletion is a group of man-made chemicals called chlorofluorocarbons
(CFCs) . These chemicals are used, among other things, as
coolants in refrigerators and air conditioners, for making plastic
foams, and a wide variety of other uses. These compounds, rising from
earth high into the stratosphere, set off chemical reactions that
rapidly destroy ozone.
Ozone (O3) in the stratosphere is created when oxygen molecules (O2 ) are bombarded with solar ultraviolet radiation. This radiation shatters the oxygen molecule O2 into two atoms of oxygen O + O ; some of the free oxygen atoms O recombine with molecular oxygen O2 to form ozone O3
The three-atom oxygen has properties that the two-atom oxygen
does not have: it can efficiently absorb ultraviolet light. In doing
so, ozone protects oxygen at lower altitudes from being broken up and
keeps most of these harmful rays from reaching the earth's
surface.
Chlorofluorocarbons
(CFCs) undergo a similar chemical reaction in the upper
stratosphere. They break up easily under the glare of ultraviolet
light. The result is free chlorine atoms (Cl) which attack
ozone (O3) to form chlorine monoxide (ClO)
and oxygen (O ) The ClO then combine with a free oxygen
atom O to form oxygen O2 and a
chlorine (Cl) atom. This is a chain reaction that repeats
itself:
Scientists found that for every chlorine atom released 100,000
molecules of ozone are removed from the atmosphere.
The danger posed by the depletion of the ozone layer to us humans, to
the earth's climates, and to life in general is such that 24
countries signed a treaty to limit and reduce the production of
CFCs.
Internet Challenge:
Grades 7 and 8
NYSLS 7: Students apply the knowledge and thinking skills of mathematics, science, and technology to address real-life problems and make informed decisions.
Objectives
Procedure
Point your browser to the following sites:
http://www.atm.ch.cam.ac.uk/tour/index.html
http://www.ec.gc.ca/ozone/
http://www.epa.gov/ozone/science/process.html
Answer the following questions
What is the ozone layer?
What is the chemistry of ozone formation and depletion?
When do CFCs become harmful?
Is the ozone layer being damaged over much of the Earth, or just over Antarctica?
How does the thinning ozone layer affect life on our planet?
Essay
After investigating the data and learning the facts, write a one page
persuasive essay to the people, businesses, and government officials
in your state explaining what we can do about ozone depletion.
Logo Simulations
Make a sketch of the chemistry of ozone formation and depletion. Use
MicroWorlds to create shapes representing atoms and molecules
involved in the ozone depletion reactions for a Logo simulation. Take
screen shots of the ozone hole over Antarctica, and any related
QTMovie to include in the program.
The following simulation was created by: Robert Jakubik, 7th grade Delta student.
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to his mother at the SchoolTech Expo |
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