In the Martian north polar region, layered deposits are an ice sheet, much like the Greenland ice sheet on the Earth.
Just as with the ice sheet in Greenland, this Martian ice sheet contains many layers that record variations in the Martian climate. Sometimes icy layers can be ablated away during warm climates. Later the ice sheet can be buried by new ice layers and grow in size again. It’s likely that many of these cycles have occurred over the ice sheet’s history.