(upbeat piano music)
- [Narrator] 15 to 35 kilometers above Earth's surface
a gas called ozone surrounds the planet.
The ozone layer acts as a barrier
between Earth and ultraviolet radiation from the Sun.
However, pollution has caused the ozone layer to thin
exposing life on Earth to dangerous radiation.
(upbeat piano music)
Earth's atmosphere is made up of six layers.
The second layer, called the stratosphere,
contains the ozone layer.
The ozone layer is made up of a highly
reactive molecule called ozone
which contains three oxygen atoms.
Ozone is a trace gas in the atmosphere.
There are only about three molecules for every
10 million molecules of air
but it does a very important job.
The ozone layer acts as Earth's sunscreen,
absorbing about 98% of damaging ultraviolet or UV light.
But the ozone layer has gotten thinner.
Chemicals called chlorofluorocarbons or CFCs
are the primary culprits in ozone layer breakdown.
A CFC is a molecule that contains the elements
carbon, chlorine and fluorine.
CFCs are mostly found in refrigerants,
aerosols and plastic products.
When CFCs are exposed to ultraviolet rays
in the atmosphere, they break down
into substances that include chlorine.
The chlorine reacts with the oxygen atoms
in ozone and rips apart the ozone molecule.
Areas of damage in the ozone layer are often
called ozone holes but that name is misleading.
Ozone layer damage is more like a thin patch
with the thinnest areas near the poles.
The ozone layer above the Antarctic in particular
has been impacted by pollution since the mid-1980s.
There the region's low temperatures speed up
the conversion of CFCs to ozone-damaging chlorine.
About 90% of CFCs currently in the atmosphere
were emitted by industrialized countries
in the northern hemisphere.
In 1989 the Montreal Protocol banned the production
of ozone-depleting substances.
Since then the amount of chlorine
and other ozone-depleting elements
in the atmosphere have been falling.
Scientists estimate that chlorine levels will return
to their natural state in about 50 years.
By then the Antarctic ozone hole will shrink
to smaller than eight million square miles.
(slow piano music)
(upbeat synthetic pop music)