If the planet Mars was able to sustain an Earth-like atmosphere, what kinds of temperatures and life could it support?

Colder, I’m sure—but let’s say it if it had (or once had) oceans and atmosphere (probably inferior to Earth’s but could sustain life)—what would the temperatures be, and what kind of plants, vegetation, and creatures could exist in, or adapt to that gravity level?

I know that life is more likely to be found in several of the moons of Jupiter and Saturn.

Any discussion is acceptable but try to keep answers consistent with Mars’ gravity, distance from the sun, and temperatures. We can also add the possibility of an ocean regardless as to whether the planet ever actually had one.