Although it is now generally accepted that water did exist on the surface of Mars, whether or not it was present long enough to foster the emersion of life is unknown. Now, with the help of a map of the minerals on the planet's surface brought back by the OMEGA instrument onboard the European Space Agency's Mars Express spacecraft, scientists suggest that Mars did have the conditions that would support life.
Based on the role water played in altering surface minerals, scientists are able to quantify how much water was present. In terms of water and geology, they concluded, Mars has three major eras. The oldest era, they say, was characterized by long-standing bodies of water and a dense atmosphere that warmed the planet enough to support life.
Following this first "warm and wet" period, the face of Mars began to change drastically as volcanoes belched out sulfur, oxidized, and formed corrosive acid rain. This conclusion stems from the spacecraft's discovery of sulfate minerals, whose formation requires a vast amount of surface water.
These conditions persisted until 3.8 billion years ago, the beginning of the third 'cold and arid' era, in which Mars still lingers, coated by a thin dust of iron-rich minerals.
One thing OMEGA did not detect were carbonate minerals – rocks suggesting the early existence of a carbon dioxide in a dense atmosphere. While the lack of carbonate discourages the "warm-and-wet" scenario, it doesn't necessarily kill the theory. If Mars experienced a massive impact or its magnetic field disappeared during the early era, the planet's atmosphere could have been swept away well before carbonate minerals could form.
Because this is in fact the dominant theory explaining the disappearance of Mars' atmosphere, scientists remain persistent in their search for evidence of life of Mars. In the future, rover-based explorations of the hydrate deposits and clay beds could reveal solid evidence for a red planet that once thrived with microbiotic life.