Why There is Almost Certainly No Life Currently on Mars

I think what a lot of people miss when they try to extrapolate extremophiles into the argument that life could exist on Mars or other seemingly hostile non-Earth planets is that the extremophiles did not originate in their current extreme environment.
Most paleobiologists agree that the reason life arose on Earth was that the "primordial soup" was perfectly suited for life. It was warm, wet, and complex organic molecules had become abundant. There was a high level of Hydrogen, Oxygen, Nitrogen, and Carbon in various forms. Hydrocarbons existed in plentiful but non-toxic supply.
There is no indication that Mars ever had this scenario. Though liquid water almost certainly existed on Mars in the distant past, it is most likely that it was highly sterile. So the problem isn't whether or not organisms exist that have the potential to survive somewhere on Mars, the problem is that Mars doesn't seem to have had a point in its history at which living organisms could arise.

"Life finds a way" Ian Malcolm mutters in the movie Jurassic Park. This may be true. But that is Life that is already here, not the genesis of Life itself.

My guess is, in the decades and centuries to come, as we discover more and more exoplanets that have terrestrial-like environments, or "Class M planets," we'll learn that only a tiny few had the necessary conditions for the arise of life. Most will be pleasant, but sterile. We will go there, or send our bacteria there, and we/they will thrive. But bacteria won't have ever arisen on those surprisingly habitable planets on their own. The conditions just weren't right.


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