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Plate Tectonics Plate Tectonics Why Continents and Ocean Basins Exist Topics • Density Structure of Earth • Isostasy • Sea-Floor Spreading • Mechanical Structure of Earth • Driving Mechanism of Plate Tectonics • Lithospheric Plate Interactions • Plate Tectonics and the Depth of the sea floor Topics • Density Structure of Earth • Isostasy • Sea-Floor Spreading • Mechanical Structure of Earth • Driving Mechanism of Plate Tectonics • Lithospheric Plate Interactions • Plate Tectonics and the Depth of the sea floor Sea-Floor Spreading Sea-Floor Spreading T h e F o r m a t i o n o f o c e a n B a s i n s t h e Continental Drift In 1912, Alfred Wegener published a book which stated that continents move In 1912, Alfred Wegener published a book which stated that continents move The concept is called continental drift 200 million years ago, all of the world’s major landmass were joined in the supercontinent of Pangaea 200 million years ago, all of the world’s major landmass were joined in the supercontinent of Pangaea Since then, the continents have drifted apart EVIDENCE Geological Evidence Climatological Evidence Geographical Evidence Paleontological Evidence Problem With Hypothesis of Continental Drift Problem With Hypothesis of Continental Drift What is the driving mechanism? Problem With Hypothesis of Continental Drift What is the driving mechanism? What makes the continents move? Problem With Hypothesis of Continental Drift What is the driving mechanism? What makes the continents move? Wegener’s suggestions for possible driving mechanisms were not plausible Problem With Hypothesis of Continental Drift What is the driving mechanism? What makes the continents move? Wegener’s suggestions for possible driving mechanisms were not plausible And most geologists did not accept continental drift Questions What does the deep-sea floor look like? Is the bottom of the deep ocean a flat, monotonous muddy plain? Sonar Sonar The development of sonar enabled oceanographers to rapidly determine the bathymetry of the sea floor Sonar The development of sonar enabled oceanographers to rapidly determine the bathymetry of the sea floor Bathymetry - measurement of water depth Sonar The development of sonar enabled oceanographers to rapidly determine the bathymetry of the sea floor Bathymetry - measurement of water depth When oceanographers conducted sonar surveys of the Atlantic in 1925, they discovered the MOR Mid-Ocean Ridge Mid-Ocean Ridge MOR is the largest geological feature on Earth Mid-Ocean Ridge MOR is the largest geological feature on Earth MOR is a long, linear feature Mid-Ocean Ridge MOR is the largest geological feature on Earth MOR is a long, linear feature Summit of MOR averages 2 km below sea level Mid-Ocean Ridge MOR is the largest geological feature on Earth MOR is a long, linear feature Summit of MOR averages 2 km below sea level Summit of the MOR is a volcanic region MOR forms in all ocean MOR is 60,000 km long Deep-Ocean Trenches Deep-Ocean Trenches Deep-Ocean Trenches Trenches are long, linear features Deep-Ocean Trenches Trenches are long, linear features Trenches are the deepest part of the ocean Deep-Ocean Trenches Trenches are long, linear features Trenches are the deepest part of the ocean As deep as 11 km (11,000 m or 33,000 ft) Deep-Ocean Trenches Trenches are long, linear features Trenches are the deepest part of the ocean As deep as 11 km (11,000 m or 33,000 ft) Trenches primarily form near the continents Most deep-ocean trenches form in the Pacific Deep-Ocean Trenches Sea-Floor Spreading Sea-Floor Spreading A hypothesis proposed by Harry Hess Sea-Floor Spreading A hypothesis proposed by Harry Hess What if the sea floor moves too? Sea-Floor Spreading A hypothesis proposed by Harry Hess What if the sea floor moves too? What if the entire crust of Earth is mobile? Sea-Floor Spreading A hypothesis proposed by Harry Hess What if the sea floor moves too? What if the entire crust of Earth is mobile? The continents drift and the sea floor spreads The Hypothesis The Hypothesis The sea floor separates at the MOR and spreads away The Hypothesis The Hypothesis Magma erupts from volcanoes at the summit of the MOR and creates new sea floor An example of sea-floor spreading - Iceland Iceland is rifting Hypothesis Hypothesis Trenches form as the sea-floor subducts into the mantle The sea floor is destroyed during subduction Sea-Floor Spreading Sea-Floor Spreading 1.Hypothesis that the sea floor spreads Sea-Floor Spreading 1.Hypothesis that the sea floor spreads 2.Sea floor is created at the MOR Sea-Floor Spreading 1.Hypothesis that the sea floor spreads 2.Sea floor is created at the MOR 3.New sea floor spreads laterally in opposite directions Sea-Floor Spreading 1.Hypothesis that the sea floor spreads 2.Sea floor is created at the MOR 3.New sea floor spreads laterally in opposite directions 4.Trenches form as sea floor subducts Sea-Floor Spreading 1.Hypothesis that the sea floor spreads 2.Sea floor is created at the MOR 3.New sea floor spreads laterally in opposite directions 4.Trenches form as sea floor subducts 5.Sea floor is destroy during subduction Sea-Floor Spreading Question Question How would you test the hypothesis of sea-floor spreading? Question How would you test the hypothesis of sea-floor spreading? JOIDES Resolution Pangaea Next Mechanical Structure of Earth