How long has the Earth's ozone layer
been there?
Atmospheric scientists believe that Earth's protective ozone
layer has been around for about 600 million years. Ozone
in the atmosphere gradually built up as a result of photosynthetic
organisms (green plants, algae, and bacteria) putting oxygen
in the air.
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Besides protecting us from ultraviolet radiation, how
else has ozone affected life here on Earth?
Without a protective ozone layer, it would have been very
difficult for life forms to make the jump from the ocean
environment to the land. Early life forms stayed submerged
in the oceans because it was water's job to protect them
from the effects of UV radiation. Once the protective ozone
layer formed, animals and plants could venture out of the
water onto the land and rapidly evolve to fill all the new
ecological niches the terrestrial environment offered.
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When and how did scientists first discover the ozone
hole?
First using high-altitude weather balloons and then satellites
orbiting high above the Earth, scientists have had an idea
that ozone was being depleted in the stratosphere
(the upper atmosphere) since the mid-1960s. But the actual
ozone
hole over Antarctica wasn't reported until 1985.
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How do scientists monitor the
level of ozone in the stratosphere?
Ozone
concentration in the upper atmosphere
is monitored by a combination of high-altitude weather balloons
and satellite images.
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Doesn't ozone get destroyed naturally
by UV radiation in the stratosphere?
While it is true that ozone
molecules
are constantly being destroyed by incoming UV
radiation from the sun, once the molecules have been
split up, they also tend to naturally recombine with each
other to produce new ozone. For the most part, under natural
conditions, the amount of ozone destroyed by radiation is
balanced by the amount of new ozone forming, so scientists
consider the total amount of ozone to be in "equilibrium."
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People mostly talk about the
ozone hole over Antarctica. Is there one over the North
Pole, too?
Indeed there is. Stratospheric
ozone depletion is happening over both poles, although
the "hole" is not as well-defined in the northern hemisphere
as it is in the south.
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Why does most stratospheric ozone depletion happen over
the poles?
Studies have shown that the cold, still air over the poles
during the long, dark winter causes a buildup of ice crystals
high in the stratosphere.
These crystals then provide a place for chlorine atoms from
CFCs (chlorofluorocarbons)
to cling on to and build up. When the spring comes and the
area begins to heat up, the ice crystals melt and the chlorine
is then released into the air. That's when the chlorine
reacts with the ozone molecules. Although there is some
ozone loss over temperate
and tropical
regions, not as much reactive chlorine accumulates because
they don't get the same buildup of ice crystals in the stratosphere
during the winter months.
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Will the ozone hole recover if we stop using destructive
chemicals?
Absolutely! In fact, since the use of some CFCs
were banned by a number of industrialized countries, the
ozone hole over Antarctica has shown signs of closing. But
the problem took years to develop, so you can't expect the
solution to happen overnight. One of the problems is that
CFCs are really stable chemicals and, once they get into
the air, it may take 50 to 100 years for them to break down.
In addition, CFCs in the troposphere (the layer of the atmosphere
close to the Earth) take time to make it up to the stratosphere
(some atmospheric scientists estimate as much as 40 years).
This means that even if we were to stop using all destructive
chemicals today, it could be as much as a century before
there is a total recovery.
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Are CFCs the only human-made
chemicals responsible for destroying the ozone layer?
No, but they are by far the biggest problem. Other destructive
chemicals include halons and bromine
(which are found in fire extinguishers) and nitric acid,
which comes from the exhaust of high-flying, supersonic
transport planes such as the Concorde. There may in fact
be more "ozone eaters" out there that scientists have not
yet identified.
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Do people with darker skin have
less to worry about from UV radiation than light skinned
people do?
All people, regardless of the color of their skin, must
be concerned about exposure to UV
radiation. However, melanin (the pigment in the skin
that gives it its dark color) does keep darker-skinned people
from getting sunburned as quickly as fair-skinned individuals
and can protect them from cancer and some of the long term
damaging effects of UV radiation. Therefore, fair-skinned
individuals need to take more care in protecting themselves
from too much sun exposure.
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Do all sunglasses help protect
the eyes from UV exposure?
While all sunglasses cut down the amount of visible light
and glare, only sunglasses that are rated for UV protection
will safeguard your eyes against the dangerous ultraviolet
part of the spectrum.
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