It is thought that Mars could someday be terraformed to resemble Earth.
Scientists believe that Mars once resembled Earth with oceans, seas, and rivers.
For some reason the planet had a complete ecosystem collapse, leaving it a barren wasteland. It seems possible. If plants were able to grow on the surface of Mars, they could suck some of the carbon dioxide from the atmosphere replacing it with oxygen. As more vegetation is added, more oxygen would be introduced into the atmosphere. In order to keep vegetation growing, the mean temperature of the planet would need to be raised to make it more hospitable to plant life and to humans.