Mars has an average temperature of -80F (-62C) - the same as the lowest temperature recorded in the Arctic revisit in 1933. And guess what? Things live in the Artic. Yes, the poles in winter can drop to -220F (-140C), but the martian lower latitudes in summer can reach +70F (21C)......
Crack out your sun lounger, factor 5000, and O2 tanks..........!
We keep basing our observations on our knowledge of the earth. Yes, not a lot will grow on earth at such extreme temperatures - but Mars is not earth and we have to think outside the box. If extremophiles (organisms that endure extreme conditions) can survive in space (in 2007, the ESA deliberately launched microorganisms on a Foton-M3 spacecraft and exposed them to the harsh vacuum of space - the lifeforms survived), which is about -455F (-270C), why not life on Mars, which is considerably warmer in comparison and actually has an atmosphere (albeit mainly carbon dioxide (95.32%), nitrogen (2.7%), argon (1.6%), oxygen (0.13%), and carbon monoxide (0.7%) along with some trace noble gasses)?
Mars formed at least 100 million years before the earth, giving any lifeforms (and we are not talking little green men or reptile-like creatures here) on the planet much longer to adapt to conditions on the planet once it started to die. It is known as 'natural evolution'. And Mars did not die suddenly. It is estimated, that through atmospheric bleeding following the loss of its magnetic field approximately 4.2 billion years ago, the planet took around 500 million years to die off.
Just because we have not found any conclusive answers yet, it does not mean that there is not the potential for life, even on a 'dead' planet like Mars.