Bad Astronomy's Phil Plait reminded readers that the "Red Planet" Mars gets its color from iron oxide (rust). Yet on ancient Mars, water was abundant and white cloud cover was present, likely giving it a more Earthly appearance. This fact prompted software engineer Kevin Gill to create images of what Mars may have looked like, using information collected by NASA with their Mars Reconnaissance Orbiter.
Gill's rendering is indeed reminiscent of Earth. One side of the planet is a vast ocean. The peaks of massive volcanoes rise above the planet's atmosphere, which was far more dense than in its current state. Gills says of his images:
"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."