Mars Recent research has confirmed the observation that extensive areas of Mars are dominated by layered terrain.
Layers exist everywhere - even within craters.
This poses two main problems, depending on the interpretation of the origin of the layers. If the layers are sedimentary , then it implies an active early sedimentary history for Mars, involving a far stronger hydrological cycle than we have evidence for. If early Mars were this active, then all the early craters should have been wiped away, yet they are largely unaffected. In addition, layering exists within many unbroken craters, without sign of an entry or exit channel. It is as if the layers had fallen from the skies.