Mars' Third Order of Relief: Regions Differentiated by Age

• Regions not evenly distributed by age or surface coverage:

• Noachian regions oldest and by far the most common (~45%)
• despite not being the longest period (~700-900 million years)
• processes include intense cratering, a planetary magnetic field, denser atmosphere, surface waters of a neutral pH (oceans, fluvial networks), volcanism (including start of Tharsis) clay formation, maybe even life
• all Noachian regions are pretty large (terra-scale)
• going from type region generally west-ish:
• Noachis Terra, Aonia Terra, Terra Sirenum, Terra Cimmeria, Promethei Terra, Tyrrhena Terra, Terra Sabæa, Arabia Terra, Margaritifer Terra, Xanthe Terra, Tempe Terra