In the rendering, a huge ocean fills one side of the planet, feeding one of the longest valleys in the solar system, Vallis Marineris. The peaks of Mars' huge volcanoes - Olympus Mons, Pavonis Mons, Ascraeus Mons and Arsia Mons - dominate the Tharsis Bulge with their peaks poking above the atmosphere. Gill imagined that the high-altitude equatorial volcanic region would likely be a desert where little vegetation would grow, whereas lower latitudes would support a wetter climate boosting the presence of greenery.
As we send more missions to Mars, it's becoming clear that the planet was once a wet world with features that were very Earth-like. For example, NASA's recently landed Mars Science Laboratory rover Curiosity touched down on an ancient riverbed inside Gale Crater where water, perhaps two feet deep, used to flow. Evidence of clays near Mars Exploration Rover Opportunity are also evidence that minerals have interacted with surface water some time in the past.
There's also evidence for huge gullies and river deltas that can be seen from orbit. Ancient coastlines have also been spotted, forming the outline of a vast ocean that likely filled the deep Vastitas Borealis basin in the northern hemisphere.
It is also known that the Martian atmosphere was a lot thicker than it is now. Over the eons, the solar wind has been eroding the upper atmosphere - as there's no global magnetic field to deflect the solar wind efficiently. So far, though, there is little evidence that the world used to support any alien flora or fauna, let alone an entire biosphere.
Although Gill is the first to admit that he made several assumptions as to what Mars might look like with an Earth-like biosphere, the image is striking.
"I am a software engineer by trade and certainly not a planetary scientist, so most of my assumptions were based on simply comparing the Mars terrain to similar features here on Earth (e.g. elevation, proximity to bodies of water, physical features, geographical position, etc) and then using the corresponding textures from the Blue Marble images," he added.
For those with a fascination for Mars, this is a wonderful alternative version of a planet that we are so used to seeing in different shades of lifeless red.