(Submitted November 07, 1996)
Why is Earth the only planet that has a ozone layer?
How come Earth is the only planet with life and water?
First of all, keep in mind that ours may not be the only solar system out
there, so who knows if the Earth is the only planet with life (or an ozone
layer). Ozone is a molecule with just three Oxygen atoms. It is created when
UV light reacts with oxygen gas, which has two Oxygen atoms. UV light also
destroys ozone, so you need just the right mix of UV light and oxygen to get
an ozone layer. Again, maybe there are some planets in other solar systems
that have the right mix.
The Earth is not the only planet with water--Mars and Venus both have water
in their atmosphere (in fact, there is a lot of water in our solar system,
for example comets are basically dusty ice balls) but it has the most liquid
water because the temperature on Earth is mostly above freezing and below
water's boiling point. To get life, you need just the right mix of materials,
like carbon, oxygen, water, etc. You also need the right temperatures for
life... most other planets are too hot or too cold. Finally, you need an
atmosphere that would protect any life from radiation. In the case of the
Earth, the ozone layer protects us from the Sun's UV light. Life is pretty
improbable because all of these things have to come together.
Andy Ptak and the Ask an Astrophysicist team
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