White veins of minerals coursing through rocks indicates that water once flowed through fissures in the rock, while large grains within the rocks themselves are rounded, suggesting that water might have dulled their sharp edges.
The area that Curiosity currently inhabits “is literally shot through with these fractures,” says John Grotzinger, the mission’s chief scientist. “Basically these rocks were saturated with water.”
Why care if water existed on Mars eons ago? For starters it could mean that some form of life was there, or possibly even still below the sub-surface in the form of fungi or other microorganisms.
Critters on Mars might even teach us how life began on Earth. If for no other reason it would be fun to watch anti-science creationists wrestle with that one.