1 Chapters 5, 6, 13, 14, 21, 22 Section 4 for Hominid evolution
2 Earth’s Interior Layers • Crust: • 5 -90 km thick • Continental and oceanic • Mantle • composed largely of peridotite • dark, dense igneous rock • rich in iron and magnesium • Core • iron and a small amount of nickel
3 Earth’s Interior Layers • Lithosphere • solid upper mantle and crust • broken into plates that move over the asthenosphere • Asthenosphere • part of upper mantle • behaves plastically and slowly flows
4 Earth’s Crust • Continental • (20 -90 km thick) • density 2. 7 g/cm 3 • contains Si, Al • Oceanic • (5 -10 km thick) • density 3. 0 g/cm 3 • composed of basalt
5 Plate Tectonic Theory • Lithosphere is broken into individual pieces called plates • Plates move over the asthenosphere – as a result of underlying convection cells
6 Geology and the formulation of theories • What is a theory? • It is arrived at through the scientific method, which involves: • • gathering and analyzing facts formulating hypotheses to explain the phenomenon testing the hypotheses and finally proposing a theory. • The hypotheses is a tentative explanation. • A scientific theory is a testable explanation for some natural phenomenon, that is supported by a large body of evidence.
7 Modern Plate Map
8 Plate Tectonic Theory • At plate boundaries • Volcanic activity occurs • Earthquakes occur • Movement at plate boundaries • Plates diverge • Plates converge • Plates slide sideways past each other
9 Plate Tectonic Theory • Types of plate boundaries Ridge Transform Divergent Cont. -Cont. Convergent Cont. -Ocean Convergent Ocean-ocean Convergent
10 The upper part of the mantle and the crust • There are convection cells (currents) in the mantle
11 • There are currents in the mantle A Subduction Zone • When the currents in the mantle carry one plate down • It melts and volcanoes are produced
12 A Subduction Zone • Sometimes the molten rock cools down below the surface
13 Continental Collision • When two plates carrying continents collide mountain chains are built
14 An Oceanic Ridge • If plates are being destroyed, new plate material must be being made somewhere else • At new plate margins
15 What Wegener knew: an example of ‘how science works’ Click on the image to launch ‘What Wegener Knew’ Power. Point
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19 Evidence for the structure of the Earth
20 Launch of a depth charge
21 Earthquake damage
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24 The lithosphere (!)
25 Evidence for plate tectonics
26 Convection in the lab
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28 Modelling the mantle
29 Mid-Atlantic ridge http: //maps. grida. no/go/graphic/world-ocean-bathymetric-map (Hugo Ahlenius, UNEP/GRID-Arendal)
30 Icelandic-type eruption Reproduced with kind permission of U. S. Department of Interior, U. S. Geological Survey
31 Black Smokers
32 Pillow lavas
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34 Research ship used to tow magnetometer
35 The equipment used
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37 Age of the sea floor © Dale S. Sawyer http: //zephyr. rice. edu/plateboundary/home. html
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42 Island arc volcanism: Zavadovski Island
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44 Ocean-continent convergence: Mount St Helens Courtesy of USGS/Cascades Volcano Observatory
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46 Folds at Lhotse (Himalayas)
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48 Plate Tectonic Theory influence on geological sciences: • Revolutionary concept • comparable to evolution • Provides a framework for • interpreting many aspects of Earth on a global scale • relating many seemingly unrelated phenomena • interpreting Earth history
49 Atmosphere Solid Earth Plate Tectonics and Earth Systems • plate tectonics is driven by convection in the mantle and in turn drives mountain building • and associated igneous and metamorphic activity • arrangement of continents affects: • solar heating and cooling, • and thus winds and weather systems • rapid plate spreading and hot-spot activity may release volcanic carbon dioxide and affect global climate
50 Biosphere Hydrosphere Plate Tectonics and Earth Systems • continental arrangement affects ocean currents • rate of spreading affects volume of mid-oceanic ridges and hence sea level • placement of continents contributes to the onset of ice ages • movement of continents creates corridors or barriers to migration, the creation of ecological niches, and transport of habitats into more or less favorable climates