Lecture 5: Plate Tectonics and Climate Last 550 Myr (chapter 4)

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Presentation transcript:

Lecture 5: Plate Tectonics and Climate Last 550 Myr (chapter 4)

Atmospheric CO 2 Evolution

Plate Tectonics Alfred Wegener (1914, German Meteorologist) proposed continental drift 1-10 cm/yr ==>5000km/100myr 2.7g/cm 3 3.2g/cm 3 >3.7g/cm 3 Soft  acts as viscous fluid allows the tectonic plates above to move

Sea floor spreading  creation/destructoin of ocean crust since 175 myr Continental magnetic field  reconstruct continental positions (lat.) since 550 myr Formation of the continents

Paleomagnetic determination of past location of continents the position of basalt rocks on (older than 175 myr) compass pointing horizontal compass pointing vertical Forming compass Molten lavas cools extruding onto the earth’s surface cools, the iron rich component aligns with the earth’s magnetic field at that time Fossil compass Further cooling forms basalts and fixes the magnetic field compasses, forming fossil compass Dating Potassium is also locked in basalts, its slow decaying rate (half time 1.3 Byr) allows us to identify the time

Magnetic reversal (over land) and magnetic lineations (in ocean) Paleomagnetic dating of ocean crust

Moving Continents 200 Myr ago 100 Myr ago Cretaceous Pangaea and Supermonsoon Gondwana and S. P. Glaciation

The Polar Position Hypothesis for alternative icehouse and greenhouse climate Glaciation occurs near polar position, But polar postion does NOT guarantee glaciation ? ? ? ? polar postion is NOT the only mechanism for glaciation What else?

Atmospheric CO2 Evolution ?? CO2? Why no ice sheet at S. Pole between Ma, Ma?

Tectonic Control of CO2 Removal: Uplift-Weathering Hypothesis Marueen Raymo et al., 1980s Uplifting ==> create fresh rock and mineral surfaces ==>stronger weathering ==> reduce CO2

The magic of “breaking up”

Quantifying weathering rate with time Why fresh rocks has a much higher weathering rate (over 100 times…) 1)Fresh rocks has more weathering materials – fresh, unweathered silicates 2)Fragmentation increases surface area 1 100

Uplift and chemical weathering

Atmospheric CO2 Evolution ??

Tectonic control of CO2: BLAG spreading rate hypothesis (Robert Berner, Antonio Lasaga, Robert Garrels, 1983) sea floor spreading ==>volcanic activity==>CO2 input

Age of sea floor

100 ma now BLAG hypothesis: sea floor spreading ==>volcanic activity==>CO2 increase CO2 Change in the last 100 myr: Hypothesis 1

BLAG hypothesis: sea floor spreading ==>volcanic activity==>CO2 increase Further weathering effect stabilizes CO2 and climate Carbon cycle and stabilization of CO2

?? Atmospheric CO2 Evolution and Tectonic control of CO2 hypothesis

References for reading Indonesian seaway, East Africa climate, and human evolution Cane M. and P. Molnar, 2001: Closing of Indonesian seaway as a precursor to east African aridification around 3-4 million years ago. Nature, 411,

Supercontinent Pangaea and Supermonsoon

Evidence of strong monsoon reversal: red beds Extreme hotness may prevent glaciation Evidence of dry continents

End of Chapter 5

Experiments in South America: More weathering on the slopes of Andes