吉林大学：《地球科学概论》课程PPT教学课件（英文版）Chapter 2：Global Tectonics Our Dynamic Planet

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Chapter 2: Global Tectonics Our Dynamic Planet

Plate tectonics From Hypothesis to Theory a Plate tectonics is a scientific theory that explains two centuries of often puzzling observations and hypotheses about our planet earth a The continents are drifting very slowly across the face of our planet a Continental drift is a concept with a long history

Plate Tectonics: From Hypothesis to Theory ◼ Plate tectonics is a scientific theory that explains two centuries of often puzzling observations and hypotheses about our planet Earth. ◼ The continents are drifting very slowly across the face of our planet. ◼ Continental drift is a concept with a long history

Plate tectonics From Hypothesis to Theory(2) a century ago geologists puzzled over the fit of the shorelines of africa and south america They noted that fossils of extinct land-bound plants and animals, glacial deposits, and ancient lava flows could be matched together along coastlines that today are thousands of kilometers apart Coal was found in antarctica Coal forms in tropical climates. implying that Antarctica has moved in the past

Plate Tectonics: From Hypothesis to Theory (2) ◼ A century ago geologists puzzled over the fit of the shorelines of Africa and South America. ◼ They noted that fossils of extinct land-bound plants and animals, glacial deposits, and ancient lava flows could be matched together along coastlines that today are thousands of kilometers apart. ◼ Coal was found in Antarctica. ◼ Coal forms in tropical climates, implying that Antarctica has moved in the past

Plate tectonics From Hypothesis to Theory 3) faced with puzzling data, scientist developed hypotheses to explain them Alfred Wegener proposed the most comprehensive early hypothesis for “ Continental drift”in1912

Plate Tectonics: From Hypothesis to Theory (3) ◼ Faced with puzzling data, scientist developed hypotheses to explain them. ◼ Alfred Wegener proposed the most comprehensive early hypothesis for “Continental Drift” in 1912

Plate tectonics From Hypothesis to Theory(4) His theory was widely rejected because: Ocean floor was too strong to be plowed aside Wegener had not proposed a plausible force that could induce the continents to drift ■ Attempts to test Wegener’ s hypothesis with observations had mixed success

Plate Tectonics: From Hypothesis to Theory (4) ◼ His theory was widely rejected because: ◼ Ocean floor was too strong to be plowed aside. ◼ Wegener had not proposed a plausible force that could induce the continents to drift. ◼ Attempts to test Wegener’s hypothesis with observations had mixed success

Plate tectonics From Hypothesis to Theory (5) The Theory of Plate Tectonics was born in 1960. Plate tectonics is the process by which Earth's hot interior loses heat We can measure the slow drift of plates worldwide using satellite navigation systems. The basic premises of plate theory are secure because they can be tested against a wide variety of observations

Plate Tectonics: From Hypothesis to Theory (5) ◼ The Theory of Plate Tectonics was born in 1960. ◼ Plate tectonics is the process by which Earth’s hot interior loses heat. ◼ We can measure the slow drift of plates worldwide using satellite navigation systems. ◼ The basic premises of plate theory are secure because they can be tested against a wide variety of observations

What Earth's Surface Features Tell Us The rocks beneath our feet are solid but they are not rigid. Topography: the relief and form of the land a bove sea level Bathymetry: topography on the ocean floor. Earth bulges around its equator and is slightl flattened at the poles. All evidence points to centrifugal force caused by Earth's rotational spin

What Earth’s Surface Features Tell Us ◼ The rocks beneath our feet are solid, but they are not rigid. ◼ Topography: the relief and form of the land above sea level. ◼ Bathymetry: topography on the ocean floor. ◼ Earth bulges around its equator and is slightly flattened at the poles. ◼ All evidence points to centrifugal force caused by Earth’s rotational spin

Isostasy: Why some rocks Float Higher Than Others a The continents average about 4.5 km elevation above the ocean floor They stand notably higher than the ocean basins because the thick continental crust is relatively light(average density 2.7 g/cm3) a The thin oceanic crust is relatively heavy (average density 3.0g/cm) he lithosphere floats on the asthenosphere

Isostasy: Why Some Rocks Float Higher Than Others ◼ The continents average about 4.5 km elevation above the ocean floor. ◼ They stand notably higher than the ocean basins because the thick continental crust is relatively light (average density 2.7 g/cm3 ). ◼ The thin oceanic crust is relatively heavy (average density 3.0g/cm3 ). ◼ The lithosphere floats on the asthenosphere

10 Highest mountain 5 Mainly Height continental crust Sea leve 5 Mainly oceanIc Depth crust 10 Deepest ocean 10 20 30 Earth's Topography is bimodal Percentage of the earth' s surface

Earth’s Topography is Bimodal

Why Earth's Topography is Bimodal? LIGHT HEAVY LIGHT HEAVYLIGHT Isostasy

Why Earth’s Topography is Bimodal? Isostasy