All planets and large moons have enough gravity to hold an atmosphere, so terraforming in theory is widely possible. But in terms of human life not all gravities are created equal. On Mars you weigh 0.38 your weight on Earth, and we're not entirely sure what this would do to human health. Mars's CO
2 atmosphere has about 1% the pressure of the Earth's at sea level. It is estimated that there is sufficient CO
2 ice in the regolith and the south polar cap to form a 30 to 60 kPa atmosphere if it is released by planetary warming.
In a nutshell: it is in theory that I can be terra formed but if it can be, forced mutations can happen due to gravity and environment, atmosphere will be cooled down if plants grow since the planet is "hot"