I thought we have found bacteria or other kinds of life on Mars.
Now it is liquid water. Is there such a big difference between liquid water and iced water?
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We have not found life, bacterial or otherwise, anywhere other than Earth ... yet. I think you mean the difference between liquid water and water ice. This difference relates to the hospitality to life. Life of the type we are used to needs liquid water, even if this is just trapped moisture, unless the life is temporarily in suspended animation. If there was no liquid water on Mars, there would seem to be no possibility of ongoing life there.
It is important to distinguish hospitable conditions from evidence for life. While having a hospitable environment is necessary for life, it is far from proof of life. The big hurdle is starting life, or bringing it from somewhere else.
There are a variety of hospitable environments in the solar system and on exoplanets, such that if certain life from Earth (such as extremophile bacteria) were somehow placed there they could live. But that does not mean there is in fact life there.
Another important point, Mars was way more hospitable early in it's history, with bodies of liquid water. Which is important because even though starting life on Mars under current conditions is unimaginable, early Mars was rather Earthlike and could possibly start, or receive, life.
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1$\begingroup$ I like this answer. One point I'd like to add is that liquid water could have sustained life on Mars while in the frozen ice caps, life would likely be preserved/frozen, but no longer evolving. That makes the very salty water kind of interesting, as it could have extended the period for the possibility of life on Mars. Not saying it did, only that it might have, if there ever was life on Mars. $\endgroup$ – userLTK Sep 30 '15 at 5:39
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$\begingroup$ @Aabaakawad Is it possible that one day human beings may prove if a place is hospitable to life, there is/was life there? $\endgroup$ – questionhang Oct 14 '15 at 7:38
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$\begingroup$ @questionhang, we would prove that by exploring hospitable places and finding life. I do not think we can possibly prove that in a theoretical way. Personally, I would be very surprised if it were true. There is the set of ideas in "panspermia" to consider, however. en.wikipedia.org/wiki/Panspermia $\endgroup$ – Eubie Drew Oct 14 '15 at 9:20
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$\begingroup$ @Aabaakawad Why are you surpised? If extremophile can survive on the Mars, more people will believe there may be life on the Mars. We have evidence that extremophile can survive on the Mars? $\endgroup$ – questionhang Oct 14 '15 at 14:49
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$\begingroup$ @questionhang, an extremophile from Earth that was salt-tolerant, somewhat UV-tolerant, and able to tolerate being freeze dried much of the time, could survive on Mars. But how would it get there? It would be by one of two methods: Either 1) a result of the creation of life on Mars billions of years ago, but we have no solid idea how that happened on Earth, which would mean we have no particular reason to think it happened on Mars. Or that 2) life came to Mars from elsewhere, most likely Earth. Both (1) and (2) are long shots. I'd be surprised if we find life on Mars. But it's not impossible. $\endgroup$ – Eubie Drew Oct 15 '15 at 3:49
