Mars' Third Order of Relief: Regions Differentiated by Age

• Regions not evenly distributed by age or surface coverage:

• Hesperian regions, middle ages, cover about 30% of the planet
• about length of Noachian, ~700-900 million years
• processes include slowdown in impacts, loss of atmosphere with collapse of magnetic field, drying up of standing water but also HUGE but brief outflows of water from magma contacting permafrost, chaos terrain, intense volcanism, acidification of groundwater, sulfate minerals
• regions fewer and smaller than Noachian ones (mostly planum/planitia-scale)
• Hesperia Planum, Malea Planum, Sisyphi Planum, Argentea Planum, Thaumasia block plana, Lunæ Planum, Chryse Planitia, Vastitas Borealis