3 Things Curiosity Found About Mars That Make the Red Planet Habitable

Acidity: Boring into Mars rock, Curiosity discovered that the sedimentary rock under study had a relatively stable and moderate pH. Many microorganisms cannot survive in extremely acidic environments; one NASA scientist described the Mars rock thusly: "This rock looks like a typical rock you'd find on Earth."

Water Activity: Scientists discovered clear indications of large-scale water activity on Mars, enough to potentially prevent cellular osmosis (cell death from not enough water) from occurring. This indicates that Mars could potentially 

Mineral Content: Some of the sample was discovered to possess a negative charge with various oxidation states. A NASA scientist described this kind of rock as essentially similar to a battery; some microorganisms could derive energy from that kind of low-level electrical charge.

To paraphrase Carl Weathers in Arrested Development:

"Whoa, whoa, whoa. There's still plenty of water in that rock. Now you take this rock home, throw it in a pot, add some stable pH, a mineral charge. Baby, you've got a primordial stew going."