QUESTION:
If iron-oxide can be created by ultaviolet radiation penetrating water is
this evidence that mars lacked an ozone layer?  Is the ozone layer a product
of life?

ANSWER from Smart Filter on August 6, 1997:
I wonder if you are putting the "cart before the horse"?  Scientists
postulate that iron oxide could have been made on Mars by ultraviolet
penetrating water, BECAUSE Mars lacks an ozone layer.  Your question seems
to ask "Do we think there is no ozone layer because we see iron oxide being
made by UV penetrating water?"

For comparison we can use a planet we know more about:  On earth, up in the
stratosphere, a molecular oxygen molecule (O2)combines with atomic oxygen
(O) to make ozone (O3).  The O3 molecule absorbs an incoming UV photon from
sunlight which causes it to break back up into O2 and O.  This chemical
cycle of creation and destruction is constantly going on in the ozone layer,
absorbing ultraviolet and thus protecting the Earth's surface from excess UV
radiation.  So, the ozone layer has given the surface the protection that
has allowed life to develop.  Mars does not have the oxygen atmosphere to
generate an ozone layer (Mars' atmospheric pressure is only about 7
millibars, whereas Earth's sea level pressure is 1013 mb., and Mars'
atmosphere is mainly carbon dioxide.)

As for your second question "Is the ozone layer a product of life?", the
ozone layer requires oxygen in the forms O, O2, and O3, and it was plant
life on earth that is believed to have changed carbon dioxide into oxygen,
so there does seem to be a connection.  For comparison, Venus which has a
very thick carbon dioxide atmosphere, has no ozone layer (so it is not just
the thickness of the atmosphere that determines whether a planet has an
ozone layer, but the composition as well).