Frozen in time: Rock fossils hint at Mars's ancient climate

Long ago, flowing wind and water shaped Mars's malleable sand and sediment into dunes, ripples and other landscape patterns, called bedforms. Over billions of years, some of these landforms hardened into rock—scientists then call them paleo-bedforms. Frozen in time, change only comes in the form of the slow erosion by dusty winds, burial by ancient lava flows or the occasional meteorite impact.