A new study may solve a central mystery of the planet's 4.6-billion-year history.
While water was present on Mars, they suggest, the liquid could have trickled through certain rock types and set off a slow chain of reactions that progressively drew carbon dioxide out of the atmosphere and converted it into methane, a form of carbon that could be stored in the clay for eons. This schematic illustrates the progressive alteration of iron-rich rocks on Mars as the rocks interact with water…