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Chapter 5 of EARTH’S CLIMATE Plate Tectonics and Climate 陳奕穎 Institute of Hydrological Sciences 1 Plate tectonic process Glaciation alternation Climate model Changes CO2 Greenhouse BLAG Spreading Rate Polar Position Hypothesis Ex: 200Myr ago Icehouse Two hypotheses Uplift Weathering Institute of Hydrological Sciences 2 Plate tectonics: The scientific theory which describe Earth is called plate tectonics. Wegener[1914] find the margins of eastern South America and western Africa, could fit together. Institute of Hydrological Sciences 3 Structure and Composition of Tectonic Plates Earth Outer Layers chemical composition Continental crust (30-70 km) Granites (花崗岩) 2.7 g/cm3 Ocean crust (5-10 km) Basalts (玄武岩) 3.2 g/cm3 Mantle (Fe, Mg) to 2890 km >3.6 g/cm3 Physical behavior Lithosphere (100 km) hard, rigid unit that forms the tectonic plates Asthenosphere (100-250 km) softer unit capable of flowing Institute of Hydrological Sciences 4 Tectonic plates The outer rigid layer of Earth is broken into about dozen major segments called plates. Institute of Hydrological Sciences 5 Plate boundaries Divergent margins Convergent margins Transform fault margins Institute of Hydrological Sciences 6 Evidence of past plate motions Earth magnetic field evidence of Plate tectonics rearranging Earth’s geography Energy from the magnetic field which result from molten fluids circulating in Earth’s liquid iron core. Institute of Hydrological Sciences 7 Magnetic lineations Molten fluid record magnetic field. Institute of Hydrological Sciences 8 Paleomagnetic determination of past location of continents Basalt is the best rocks to use (rich in highly magnetic iron). No ocean crust older than 175 Myrs. For earlier interval, it must focus on basalts on the continent. 500Myrs less reliable because of increasing likelihood that their magnetic signatures have been rest to the magnetic field of a later time. Institute of Hydrological Sciences 9 Short Summery We can reconstruct the position of the continents with good accuracy back to 300 Myrs ago. To measure rates of the seafloor spreading in ocean basin. Even we can compile spreading rates over enough of the world’s ocean to estimate the global mean rate of creation and destruction of ocean crust. Institute of Hydrological Sciences 10 The Polar Position Hypothesis : ice sheets should appear on continents when they located at polar or near-polar latitude, but no ice should appear anywhere on Earth if no continent exist anywhere near poles. Institute of Hydrological Sciences 11 Moving continents Institute of Hydrological Sciences 12 Pengaea Laurasia: North-central Asia, Europe, North American Gondwana: Africa, Arabia, Antarctica, Australia, South America, and India. Laurasia Gondwana Institute of Hydrological Sciences 13 Gondwana and South Pole Institute of Hydrological Sciences 14 Glaciations and Continental Positions since 500 Myr Ago Why ? CO2 Icehouse Greenhouse Institute of Hydrological Sciences 15 Modeling Climate on the Supercontinent Pangaea Climate scientist use general circulation models (GCMs) to evaluate the impact of geography as well as several other factors. Questions: What level of atmospheric CO2 ? Dose it match geologic record ? Institute of Hydrological Sciences 16 Input to the Model Simulation of Pangaean Climate Boundary condiction: 1. Distribution of land and sea 2. Global sea level 3. Topography Using simplified symmetrical 1000 m Comparable to today’s 200 Myr ago Institute of Hydrological Sciences 17 Input to the Model Simulation of Pangaean Climate cont. 4.Climate modelers constrain the likely CO2 level in atmosphere. 5.Astrophysical modelers indicate Sun’s energy weaker 1% than today’s. Institute of Hydrological Sciences 18 Output from the Model Simulation of Pangaean Climate Dry continental Downward Uplift climate 1.the great expanses of land at subtropical latitudes beneath the dry. 2.trade wind lose most of their water vapor by the time they reached the continental interior Institute of Hydrological Sciences 19 Output from the Model Simulation of Pangaean Climate cont. Monsoon circulations Different rates of response of the land and sea to heating in summer and radiative heat loss in winter Institute of Hydrological Sciences 20 Tectonic Control of CO2 Input BLAG[1983] (the geochemists Robert Berner, Antonio Lasaga, Robert Garrels) Climate changes during the last several hundred million years have been driven mainly by changes in the rate of CO2 into the atmosphere by plate tectonic process.(spreading rate hypothesis) Spreading rates Change CO2 Climate change Institute of Hydrological Sciences 21 Age of the seafloor Spreading rates are as much as ten times faster in the Pacific than in Atlantic. Institute of Hydrological Sciences 22 Earth’s Negative Feedback Institute of Hydrological Sciences 23 Tectonic-scale Carbon cycle Chemical weathreing on land CaSiO3 CO2 CaCO3 SiO2 Silicate rock Atmosphere Plankton Plankton Meltimg and transforma tion in subduction zone CaSiO3 SiO2 SiCO3 CO2 Ocean sediment Silicate rock Atmosphere Imbalance CO2 Climate changes Institute of Hydrological Sciences 24 A Warmer Earth 100Myr Ago The global mean spreading rate was as much as 50% faster 100Myr ago than it is at present, so the rate of input of CO2 from the rocks to atmosphere must be higher than today. Institute of Hydrological Sciences 25 The Uplift Weathering Hypothesis Chemical weathering Rock exposure Fresh rock Exposure time Institute of Hydrological Sciences 26 Fragmentation of Rock Weathering and Exposure Time Institute of Hydrological Sciences 27 Three Hypotheses: Institute of Hydrological Sciences 28 Conclusions: Plate tectonic process largely explains alternations between icehouse intervals. Atmospheric CO2 changes in tectonic-scale in the last hundred million years needed to explain the climate variability. Both spreading rate & uplift hypotheses attempt to link the changes in CO2 and in plate tectonic. Institute of Hydrological Sciences 29