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Plate Tectonics and Climate
陳奕穎
Chapter 5 of EARTH’S CLIMATE
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Plate tectonic process
Glaciation alternation
Climate modelChanges CO2
IcehouseGreenhouse
Ex: 200Myr ago
Two hypotheses
Polar Position Hypothesis
BLAG Spreading Rate Uplift Weathering
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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.
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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
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Tectonic plates
The outer rigid layer of Earth is broken into about dozen major segments called plates.
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Plate boundaries
Divergent margins Convergent margins Transform fault margins
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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.
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Magnetic lineations
Molten fluid record magnetic field.
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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 contin
ent. 500Myrs less reliable because of increasing likelihood t
hat their magnetic signatures have been rest to the magnetic field of a later time.
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Short Summery We can reconstruct the position of the continents wit
h good accuracy back to 300 Myrs ago. To measure rates of the seafloor spreading in ocean b
asin. 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.
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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.
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Moving continents
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Laurasia
Gondwana
Pengaea Laurasia: North-central Asia, Europe, North American Gondwana: Africa, Arabia, Antarctica, Australia, Sout
h America, and India.
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Gondwana and South Pole
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Glaciations and Continental Positions since 5
00 Myr Ago
Why ?
CO2
Icehouse Greenhouse
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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 ?
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Input to the Model Simulation of Pangaean Climate
Boundary condiction:Distribution of land and sea
Global sea level
Using simplified symmetrical
Comparable to today’s
200 Myr ago
Topography
1000 m
1.
2.
3.
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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.
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Output from the Model Simulation of Pangaean Climate
Dry continental 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
Uplift
Downward
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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
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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 Climate changeCO2
Change
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Age of the seafloor
Spreading rates are as much as ten times faster in the Pacific than in Atlantic.
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Earth’s Negative Feedback
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Tectonic-scale Carbon cycle
2323 SiOCaCOCOCaSiO
landonweathreingChemical
Silicate rock Atmosphere Plankton Plankton
2323 COSiCOSiOCaSiO
zonesubductionintiontransformaandMeltimg
Ocean sediment Silicate rock Atmosphere
Imbalance CO2
Climate changes
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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.
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The Uplift Weathering Hypothesis
Chemical weathering
Rock exposure
Fresh rock
Exposure time
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Fragmentation of Rock
Weathering and Exposure Time
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Three Hypotheses:
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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.
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