Layers as a Key to the Martian Past

Layers underlie Noachian and
Hesperian surfaces; may be 
predominantly Noachian

Valles Marineris stratigraphy
is key to understanding 
Noachian climate and 
processes

If predominantly lava, this provides a constraint on volatile release and supports the interpretation that bulk of the Tharsis bulge is Noachian (Phillips et al. 2002)

If these are predominantly aqueous sediments like the Grand Canyon, then a dramatically different geologic history is required