Ice Ages
اسلاید 1: Ice AgesPleistocene 3 M.y. Permian 250-220 M.y. Ordovician 450 M.y. Precambrian 900-650 M.y. (Snowball Earth)2300 M.y.
اسلاید 2: Time (1000 Years)North AmericaAlpsNorthern EuropePoland-Russia0-18Interglacial Interglacial Interglacial Interglacial 18-67WisconsinWurmVistulaVarsovian67-128SangamonUznachEemMasovian128-180IllinoisanRissWarthe/SaaleCracovian180-230YarmouthHoettingHolsteinSandomirian230-300KansanMindelElsterJaroslavian300-330AftonianCromer Likhvin330-470Nebraskan GunzMenapian470-540Waalian540-550Donau IIWeybourne550-585Tiglian585-600Donau I600-2000About 20 Glacial AdvancesAbout 20 Glacial AdvancesAbout 20 Glacial AdvancesAbout 20 Glacial Advances2000 (2 M.Y.)Beginning of PleistoceneBeginning of PleistoceneBeginning of PleistoceneBeginning of Pleistocene4000 (4 M.Y.)Dwarf forests still in AntarcticaDwarf forests still in AntarcticaDwarf forests still in AntarcticaDwarf forests still in Antarctica15 M.Y.First Glaciation in Antarctica First Glaciation in Antarctica First Glaciation in Antarctica First Glaciation in Antarctica
اسلاید 3: The Last 800,000 years
اسلاید 4: Beginning of the Ice Ages
اسلاید 5: Milankovich CyclesCool Summers More Important Than Cold WintersTilt of AxisShape of Orbit PrecessionCan’t be the whole story-have operated throughout earth history
اسلاید 6: Axis TiltSmall Axis Tilt: Mild winters but cool summers. Favors Ice Age Large Axis Tilt: Cold winters but hot summers. Favors Interglacial
اسلاید 7: Axis Tilt and the Incredible Shrinking TropicsEarth’s Axis Tilt is Shrinking24.2 degrees 9,500 years ago23.4 degrees now22.6 degrees 10,200 years from nowTropics are shrinking14.7 m/year = 4 cm/day = 1.7 mm/hourTemperate zones gain 1550 sq km/year1080 at the expense of tropics470 at the expense of Arctic and Antarctic
اسلاید 8: Precession: 26,000 year cycle
اسلاید 9: Shape of Orbit + PrecessionSummer at Perihelion (Eccentric Orbit) Cold winters but hot summers. Favors Interglacial Summer at Aphelion (Eccentric Orbit) Near-circular Orbit Mild winters but cool summers. Favors Ice Age
اسلاید 10: The Greenhouse EffectWithout a natural Greenhouse Effect, earth would be frozen90% due to Water VaporOther contributors: carbon dioxide, methane, nitrous oxides“A little Greenhouse Effect is a good thing”Carl SaganProblem: we are accelerating it with unknown final consequences
اسلاید 11: The Carbonate-Silicate CycleEarth has almost as much carbon dioxide as VenusVolcanoes add carbon dioxide to the atmosphereCarbon dioxide is removed from the air to make carbonate rocks“Icehouse” and “Greenhouse” episodes
اسلاید 12: The Carbonate-Silicate CycleMountain-building favors coolingUplift exposes rocks to weatheringCalcium silicates (plagioclase, amphiboles, pyroxenes) are chemically weatheredCalcium is carried to the sea where organisms bind it into carbonate mineralsCreation of carbonates removes carbon dioxide from the atmosphereWeathering of carbonates returns carbon dioxide to the atmosphere
اسلاید 13: The Carbonate-Silicate CyclePlate tectonics carries some carbonates into the earthHeat liberates carbon dioxideCarbon dioxide returns to the atmosphereThe cycle does not require life but does require liquid water.
اسلاید 14: The Snowball EarthBetween 900 and 600 m.y. ago, Earth froze completely (or almost) about four timesGlobal freezing alternated with extremely rapid sea-level rise and global warmingEvidence:Glacial deposits on all continents, even at low latitudesGlacial deposits immediately succeeded by thick deposits of carbonate rocks
اسلاید 15: The Snowball EarthPossible reasons: Fainter early sun Biological changesGlobal ice coverWeathering and erosion shut downVolcanoes continue to erupt CO2At 10% CO2, abrupt warming beginsGo from –50 C to +50 C in 10,000 years?Implications for life?
اسلاید 16: What Causes Ice Ages?Within Earth (Endogenic)Carbonate-Silicate Cycle Volcanic Eruptions - Sudden output of CO2 (warming) or particulates (cooling) Mountain Building - Changes in atmospheric circulation Continent-Ocean configuration Outside Earth (Exogenic)Changes in Sun (faint early sun) Variations in Earth Orbit (Milankovitch Cycles) Dont Really Know
اسلاید 17: Are We Headed For Another Ice Age?Heating & Cooling in Historic Times Smoke, Haze, CO2 May Alter Climate Dont Really KnowGlobal warming due to fossil fuels may be catastrophic in many ways, but will probably not much affect these longer-term cycles. We will have run out of fossil fuels long before the duration of a typical interglacial.
اسلاید 18: This powerpoint was kindly donated to www.worldofteaching.comhttp://www.worldofteaching.com is home to over a thousand powerpoints submitted by teachers. This is a completely free site and requires no registration. Please visit and I hope it will help in your teaching.
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