Hi. So what'ya think? I've always been fascinated by this! The main problems are:
Very weak magnetosphere
The temperature and air-pressure problems are linked and could be solved by a heating up the planet. Any good ideas?
But, the main obstacle is Mars' very nasty air composition. Once the problem of heating up the planet has been solved, what to do next? The atmosphere would be made up of practically only carbondioxide. Even if plants and microbes are successfully introduced at some point, and the concentrations of oxygen significantly increased, the air would still be poisonous.
Also, what effect would the radiation due to Mars' weak magnetosphere actually have on living organisms? http://www.universetoday.com/14979/mars-radiation/
according to this, the radiation isn't so bad. Typically at 0.002 rads per day, and much of it are + charged ions so not as lethal as 0.002 rads of high-frequency electromagnetic radiation.
Would plants n organisms, assuming the air-pressure of Mars reaches acceptable levels and that there is ample supply of water, nitrogen and other stuff, be able to thrive on Mars?