Update (12/23): Credited image (full of microscopic life) below.
Regardless of whether or not you believe that the red planet is the future of humanity, one thing is probably certain–whether it takes a decade or a millennium, humanity will probably settle upon that dusty crimson world.
If humanity ever does gain the necessary technology to terraform Mars into a habitable world (air pressure and temperature wise), we may discover that although the red planet makes an excellent habitat for terrestrial vegetation, it may make an extremely poor one for colonists and animals.
One of the key ingredients for animal life on our planet is oxygen. Without it, most creatures would experience a short (but painful) death, leaving the insects to rule the planet.
Thanks to the laws of photosynthesis, plants are able to produce a large enough volume of oxygen to enable animals, space geeks and people to thrive upon planet Earth.
Most of this oxygen however does not come from land plants, such as trees, grass, etc., but rather from a single celled organism called Phytoplankton which contributes between 70% and 90% of the worlds oxygen from the ocean.
Image Credit: Prof. Gordon T. Taylor, Stony Brook University, USA (via NOAA Photo Library)
While land plants do contribute their fare share of oxygen for our planetary survival, they may not be as effective on Mars which receives half the amount of sunlight as Earth (which could easily translate into less oxygen for our lungs).
Although Mars currently lacks large oceans like its bigger bluer brother, the red planet does contain an abundance of water that if melted could flood the planet.
While this may make it an ideal candidate to host Phytoplankton within Martian waters, it may not be a realistic scenario considering that the red planet could contain an abundance of perchlorate within its soil, which is deadly to most terrestrial life forms.
Image: Soil samples from “Snow White” trench, taken on July 8, 2008, were found to contain perchlorate after analysis in the Phoenix Mars Lander’s Wet Chemistry Laboratory. (Photo by NASA/JPL-Caltech/University of Arizona/Texas A&M University)
If Phytoplankton were to even survive within future Martian oceans, humanity would probably have to find some way to heavily filter out perchlorate from the soil in order to prevent it from contaminating the future “red” oceans of Mars.
Although these two dilemma’s may not be enough to discourage humanity from creating an eden out of this crimson world, the lack of a sizable moon may present a unique challenge for our rowdy species.
Image Credit: How Stuff Works.com
Without a strong gravitational pull future Martian oceans could eventually become stagnant overall, making it extremely difficult (if not impossible) for certain species to survive, which could limit which animals we could bring thanks to the circle of life.
Even though these three challenges may prevent humanity from turning Mars into a second Earth, it probably would not be enough to prevent the masses from settling this planet.
While large forests may be able to survive on the planet due to a (future) rich atmosphere of COs, humans may have to be content living within biospheres along with their animal friends (pets and pigs alike).