NASA's latest findings from its MSL Curiosity Rover expedition on Mars shows that the planet once was suited for microbial life. A sample analysis of rock powder in the Yellowknife Bay area revealed traces of sulfer, nitrogen, hydrogen, oxygen, phosphorus, and carbon, as confirmed by Curiosity's numerous data instruments. These chemical ingredients, essential to life as we know it on Earth, were situated in an ancient stream bed flush with clay minerals--a product of flowing water that dried up in Mars' ancient past. Scientists at the MSL laboratory have concluded that these conditions would have been favorable for life. The sample analysis "indicate a habitable environment characterized by neutral pH, chemical gradients that would have created energy for microbes, and a distinctly low salinity, which would have helped metabolism if microorganisms had ever been present."
In the photo above, NASA compares rocks seen by Curiosity (on the right) with those studied by the Opportunity rover on another part of Mars (photo taken in 2004). With both show sulfate-rich sandstone and particles formed int eh presence of water, the rocks observed by Opportunity are thought to be in an inhabitable environment because of high water acidity and "extreme salinity that would have impeded microbial metabolism."