"You need so much water that we think these could be evidence of an ancient warmer and wetter climate where there was rain falling for millions of years."

Bleached Martian rocks offer fresh evidence of a wetter and warmer Mars: 'But where did they come from?

Source: space
Source Link: https://www.space.com/astronomy/mars/bleached-martian-rocks-offer-fresh-evidence-of-a-wetter-and-warmer-mars-but-where-did-they-come-from