Give me the reasons why humans cannot sustain their own life on mars

1) there is no oxygen
2) there is no atmosphere and so the pressure is too great (e.g.: our heads will explode without protective equipment)
3) there is no atmosphere so plants can't grow and if there are no plants then animals can't survive
4) plants and animals couldn't survive because there is no water apart from the water they think is there
5) no gravity- we wouldn't want water to float away and plants & animals couldn't survive if they were floating away

There is oxygen on mars. It may not be free oxygen, but it's there, and could be freed.

You'll have to do better in thinking rigorously. You can do it.

Holy cow -- Cosmo knows what he's talking about, but Charizar got all his answers wrong in one way or another.

the technical , economical and social/cultural(probable one way trip) problems of sending a person to mars are so great that we will not need to worry about it for 100 years or more

How Do You Know Colonies Don't Already Live There .
Mars Is Alive As Earth Is , My Friend.

And Life Is On Ceres , The Planet Between Mars & Jupiter .

Mars is too cold at night, there is no water there either.

It's colder than Antarctica and has much, much less air than the top of Mt. Everest.