"Raven" ro.com wrote in
message ...
"Steen Eiler Jørgensen" skrev i en
meddelelse
. ..

Should human activity on Mars bio-contaminate the surface, it should be
no
problem for a trained biologist to spot the difference between
terrestrial
microbes and organisms never encountered before.

Not necessarily. If Terran microorganisms are introduced to Mars, and
some of them survive and actually grow, they will be subject to an
enormous
selection pressure. A few decades might change them beyond easy
recognition. Do microorganisms have enough junk DNA,

I wish people would stop calling the "non protein coding" part of DNA for
junk.
See e.g. Scientific American, nov 2003 for the latest on this.

which is not subject
to selection pressure, to establish kinship?

hmmm, again I think you are assuming junk here. As it is not (junk), it must
be fair to argue that there is selection pressure on these parts as well.

Also, there is the possibility that Earthlife has already been
introduced
to Mars, a very long time ago.

And hopefully more to come! Ok, lets scan Mars for life, but surely it
shouldn't hold back exploration of the planet.

-Simon