Terraforming: making an Earth of Mars

As we understand more about life on Earth and about the chemical and biological potential of other planets and objects in our solar system, it's not too much of a leap to consider creating a habitable environment on another planet. Scientists have begun to ponder the possibility of transforming Mars, the most Earthlike of the nearby planets. Various scenarios have been proposed, and in many ways these scenarios duplicate the processes that transformed the early Earth. Here we look at some of the possibilities.