12/3/09 1 Chapter 20 ?? Evolu4on of Earth?s Atmosphere: ??The ?rst atmosphere at planet forma4on (4.57 Ga): ?? Hydrogen and helium, Quickly stripped o? by the solar wind. ??A secondary atmosphere developed via volcanism. ?? Volcanic gases dominated (mostly Water (H 2 O) and Sulfur dioxide (SO 2 )), but also ??Carbon dioxide (CO 2 ). ??Nitrogen (N 2 ). ??Ammonia (NH 3 ). ?? Free oxygen (O 2 ) was absent . ?? Condensed water fell as rain to form the oceans. ?? Atmospheric CO 2 decreased by dissolving in ocean water. ?? CO 2 removal permiXed atmospheric cooling. ?? The rela4ve abundance of stable N 2 increased. Chapter 20 ?? Evolu4on of Earth?s Atmosphere (cont): ?? By 3.5 Ga, photosynthe4c cyanobacteria added free O 2 . ?? Atmospheric O 2 accumulated. ?? By 2 Ga, O 2 reached 1% of present value. ?? Eukaryo4c green algae (1.6 Ga) accelerated O 2 produc4on. ?? By 600 Ma, O 2 arrived at 10% of present concentra4ons. ?? Peaked during the late Paleozoic and declined sharply in the early Mesozoic. ?? Present O 2 concentra4on (20.9%) by 400 to 250 Ma. ?? O 2 buildup permiXed diversi?ca4on of life. ?? Aerobic (oxygenated) respira4on is more energy?e?cient. ?? Aerobic respira4on fueled mul4cellular life. ?? O 2 opened the possibility of land?dwelling biota. ?? O 2 made forma4on of the ozone layer possible. »? Ozone absorbs deadly ultraviolet (UV) radia4on. »? Prior to the ozone layer, exposed land was bathed in UV Chapter 20 ?? The present atmosphere: ??Nitrogen (78%), Oxygen (21%), Other gases (1%) ??Aerosols (Liquid droplets. Solid dusts.) ??Pollutants ?? Created by Fossil fuel combus4on & Industrial processes ?? Acid rain ?? Greenhouse gases ? CO 2 and CH 4 trap atmospheric heat. ??Atmospheric color ?? Light is scaXered as it passes through the atmosphere. ?? Some light returns to space. ?? Why is the sky blue?: sun overhead = gases scaXer blue light. ?? Why is the sky red? sejng Sun passes through thicker atmosphere, Blue is scaXered to space. Chapter 20 ?? Adiaba4c Hea4ng/Cooling ?? Air up = expansion and cooling, Air down = contrac4on and warming ?? Rela4ve Humidity ?? Saturated versus unsaturated ?? Dew point ?? Cloud forma4on ?? Latent Heat ?? Evapora4on takes heat, Condensa4on releases heat ?? Atmospheric Layers ?? Thermal: troposphere> stratosphere>mesosphere>thermosphere ?? Boundaries are ?pauses? ?? Mixing: Homosphere/Heterosphere ?? Ionosphere (mesosphere/thermosphere) 12/3/09 2 Chapter 20 ?? Atmospheric Circula4on ?? Air movement in troposphere (wind) caused by varia4ons in pressure (high to low) ?? Pressure varia4ons driven by solar energy input (insola4on) ?? Seasonal energy varia4ons, Earth?s 4lt ?? Coriolis E?ect: Right hand rule ?? Convec4on Cells ?? Air?ow from hot to cold plus coriolis ?? Hadley, Ferrel and Polar Cells ?? Convergence zones ?? Sinking versus liqing, deserts versus tropics ?? Prevailing surface winds ?? Trades, westerlies, polar high ?? Jet streams Chapter 20 ?? Weather ?? Convergence of moving air masses = fronts ?? Cold front, warm front, occluded front ?? Rota4onal ?ow (spiral down = high pressure, spiral up = low) ?? Ver4cal mo4on up (liqing) causes clouds ?? Convec4on, frontal, convergence, orographic ?? Storms ?? Strong low pressure, cold fronts ?? Lightening and tornadoes ?? forma4on ?? Hurricanes ?? Structure and cause (the ocean heat engine) ?? The di?erence between weather and climate ?? Major controls on climate (la4tude, topography, circula4on (ocean and atmospheric) Chapter 22 ?? Theory of Glacia4on ?? Louis Aggassiz ?? Geomorphologic evidence ?? Ice Ages ?? Cold and warm periods have occurred since the Earth formed ?? Current ?warmer? period (interglacial) started about 10K ybp (ie. the Holocene) ?? Glaciers and ice sheets ?? Cover 10% of Earth?s land area ?? Mountain glaciers ?? Con4nental Glaciers (ice sheets) ?? Coverage a whole con4nental or large island ?? Today only Greenland and Antarc4c Ice Sheets are leq ?? Thermal categories ?? Temperate versus polar Chapter 22 ?? Forma4on of glaciers ?? Equilibrium (snow) line al4tude ?? Snow> ?rn> ice ?? Glacier ?ow ?? Gravity driven ?? BriXle at top (crevasses), duc4le below ?? Behaves like a viscous ?uid ? Think of pouring honey on a table ?? Deforma4on plus basal sliding ?? Glacier Mass Balance ?? Accumula4on and abla4on ?? Advance and retreat ?? Floa4ng Ice ?? Ice shelves, ice tongues ?? Icebergs ?? Sea Ice 12/3/09 3 Chapter 22 ?? Glacial Landscapes ?? Erosion mechanisms ?? Entrainment ?? Plucking & Quarrying ?? Abrasion ?? Erosional Features ?? Cirques, Tarn Lakes, Aretes, Horns, U?shaped valleys, Hanging valleys, uords ?? Transport ?? Ice surface = medial and lateral moraines ?? Interal and basal load ?? Deposi4on ?? Till ?? Moraines (ground and end) ?? Erra4cs ?? Glacial marine ?? Glacial outwash ?? Stra4?ed and sorted sand and gravel ?? Glacial lacustrine ?? loess ?? Glacial landforms ?? Moraines, drumlins, keXle lakes, eskers Chapter 22 ?? Glacial Istostacy ?? Sea Level Rise ?? Drainage Diversion ?? Pro?glacial lake forma4on and drainage ?? Clima4c changes ?? Periglacial environments ?? The Pleistocene Glacia4on ?? Loca4on of major ice sheets ?? Northern hemisphere more ice expansion because of more con4nent area ?? Impact on North America ?? Southern limit of advance (end moraine loca4ons) ?? Periglacial environmrnts ?? South western climate ? weXer, pluvial lakes. Chapter 22 ??Cause of Glacia4ons ??Milankovitch cycles ??Eccentricity, obliquity, precession ??Varia4ons in albedo, ocean thermohaline circula4on, CO2 varia4ons ??Plate Tectonics = Cenozoic Cooling ??Closing of the Mediterranean ??Separa4on of Antarc4ca and South America ??Upliq of Himalayas ??Connec4on of North and South America Ian Howat chapters20&22.pptx
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