Current knowledge suggests there is plentiful water ice at the Martian poles. The same knowledge says it gets cold enough at the poles for carbon dioxide to freeze out of the air. If creating a habitat towards the equator of Mars (to have slightly warmer temperatures) we will need to get these gases somehow closer to the habitat.
Oxygen and hydrogen combine to form water. These are probably the most critical elements required in large quantities to sustain human life. Oxygen to breathe and hydrogen to combine with oxygen to make drinking water.
How much soil would need to be processed to extract a gallon of water?
How much soil would need to be processed to fill a 10' x 10' X 10' room with the same amount of oxygen in the same room on Earth?