posted from rec.org.mensa

(me)

We flatter ourselves that extraterrestrials would be interested in
> > humans,
> > other mammals or any of the vertebrates.
> > Perhaps they are more interested in some of the invertebrates. Ants
> > perhaps,
> > or the intelligent octopus?
> > If they are looking for the Ammonites, they have taken much too long on
> > the
> > journey from wherever.
>
> > Or even Earth's bacteria and viruses. The extraterrestrials themselves
> > could
> > be some of those, hitching rides on comets and floating down through our
> > atmosphere.
--------------------------
Aren't aliens just people from other planets?
>
> Mitch Raemsch
> ---------------------------------------
(me)
> Life might have started on other planets (outside our Solar System) as
> viruses or simple bacteria-like organisms. But there is little chance that
> it would evolve into anything resembling life on earth. Conditions would
> be
> different.
> The Octopus has copper-based rather than iron-based blood, hemocyanin
> rather
> than haemoglobin.
> An alien being might have some other form of biology, perhaps with
> elements
> that don't exist on Earth.
>
> Water is necessary for life here. Stromatolites, a very early form of
> life,
> evolved in Shark Bay, Australia. (They are still there).
> Unless there are oceans, advanced life would not go through a fish stage.
> Reproduction too would probably be very different. Fluid of some kind,
> internal or external, is necessary.
> Offspring might be budded off or some similar system.
>
> The chance of human-like aliens existing elsewhere, and being able to
> cover
> the incredible distances measured in light years from distant planetary
> systems, is probably nil.
>
> And when we humans become extinct it may take millions of years, if ever,
> for any
> other creature to evolve as we did
------------------------------------
I think it is just the reverse. Life has universal form; like a
dolphin. Evolution tends to do the same thing.

Mitch Raemsch

__________________
(me)
That happens on Earth, with our conditions. Dolphins and penguins have much
in common.
And placental mammals and marsupials can be much alike in form and habits.
Even ocean dwellers with gills and land creatures with lungs have much of
their DNA in common, and need oxygen.

But creatures evolving on a planet outside the solar system would be adapted
to different conditions.

Here, we are worrying about an increase in CO2, methane etc. On Mt Everest
the oxygen level is so low that climbers need oxygen supplied.
If a small difference in our planet's atmosphere can cause problems, what
would an alien atmosphere be like?
Advanced creatures which evolved on Mars (if any existed) would be unable to
exist
in our world without some form of space suit, as we could not exist there.
(There might just be a possibility for viruses or simple anaerobic bacteria
to
exist on both worlds.)

How much different would it be for creatures from a methane or helium
atmosphere, or from planets with extreme heat, cold or radioactivity?

And they would have to travel through light years in space. Gravitational
fields, radioactivity, meteorites and other space junk would be likely to
damage whatever vehicle they were travelling in.
Suspended animation could prevent the need for many generations of
reproducing organisms during a journey of millennia. But would that be
possible? And the mechanisms for "waking" the travellers might not work
after so long.

Science fiction solves the problems with space warps and drives, and we
accept that convention for the sake of the stories.
But reality would be very different.

(added)
Time travel has the same problems, apart from the paradoxes involved.

If we went back to any time before about three thousand years ago we wouldn't be
able to communicate with the ancient peoples, as the languages have changed
so much. How would we get on in Ur or Troy?
And even back is Shakespeare's time, we would probably be considered in league with the Devil and killed.