Geography on Mars Third Order of Relief Los

Geography on Mars: Third Order of Relief Los Angeles Geographical Society 6 March 2015 Dr. Christine M. Rodrigue Geography California State University, Long Beach

Geography on Mars • Third order of relief and deep time on Mars – Geological periods (actually eons in Earth terms) _ Noachian period: formation of planet 4. 6 Ga to tapering off of the Late Heavy Bombardment of the solar system ~3. 75 Ga _ dense cratering of a wide variety of sizes _ planetary magnetic field starts and collapses _ denser atmosphere, possibly warmer _ above water's triple point _ ground and surface water: • ocean, seas, and lakes • valley networks _ neutral or alkaline hydrochemistry (phyllosilicate clays) _ volcanic activity starts and then concentrates spatially _ only period potentially friendly to life "as we know it, Jim"

Geography on Mars • Third order of relief and deep time on Mars – Geological periods (actually eons in Earth terms) _ Hesperian period: until ~3. 5 to 1. 8 Ga; most commonly thought to fade out around 3. 0 Ga _ impacts fewer and smaller _ loss of atmosphere with loss of magnetic field _ surface waters lost to space, permafrost, ice caps _ volcanism (and sulfur dioxide) _ volcanic activity focusses on Tharsis and Elysium _ sulfate hydrochemistry (very acid, hostile to life) _ different mineralogy: sulfates, evaporites _ outwash floods as magma interacts with permafrost

Geography on Mars • Third order of relief and deep time on Mars – Geological periods (actually eons in Earth terms) _ Amazonian period: "young" Mars, from ~3. 0 Ga to today _ Cratering low level, low size _ May be dampening of slopes by groundwater seeps _ There is evidence of recent volcanic eruptions but not at Noachian or Hesperian levels _ Giant outflows may occasionally occur _ Ice ages may occur due to axial and orbital changes _ Wind is the dominant agent, however • Dust devils are very common • Occasionally, planet-covering dust storms _ Geochemistry is dominated by oxidation of iron into anhydrous oxides, creating reddish dust

Geography on Mars • Third order of relief and deep time on Mars – Geochemical periods (just to stir the pot) _ Phyllosian period: time of the phyllosilicate clays • Up to late Noachian, when volcanism took off and pumped out so much sulfuric acid into the atmosphere • These clays form in neutral or alkaline surface or subsurface waters _ Theiikian period: time of the sulfates • Late Noachian/much of the Hesperian • Sulfate minerals and evaporites form from a lot of water • Acidic conditions (related to volcanism) • Hydrated sulfates (gypsum, magnesium sulfate) _ Siderikian: time of iron oxidation • Late Hesperian and the Amazonian • Oxidation of iron-rich rocks

Third Order: Deep Time on Mars

Third Order: Varying Crater Densities • Noachian Hesperian Amazonian

Third Order: Noachian Regions

Third Order: Hesperian Regions

Third Order: Amazonian Regions