Chapters 5, 6, 13, 14, 21, 22 Section 4 for Hominid evolution 1

Earth’s Interior Layers Crust: 5-90 km thick Continental and oceanic 2 Mantle composed largely of peridotite dark, dense igneous rock rich in iron and magnesium Core iron and a small amount of nickel

Earth’s Interior Layers 3 Lithosphere solid upper mantle and crust broken into plates that move over the asthenosphere Asthenosphere part of upper mantle behaves plastically and slowly flows

Earth’s Crust Continental 4 (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

Plate Tectonic Theory Lithosphere is broken into individual pieces called plates 5 Plates move over the asthenosphere –as a result of underlying convection cells

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. 6

Modern Plate Map 7

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 8

Plate Tectonic Theory Types of plate boundaries Transform Divergent Cont.-Cont. Convergent Cont.-Ocean Convergent Ocean-ocean Convergent Ridge 9

There are convection cells (currents) in the mantle The upper part of the mantle and the crust 10

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 11

A Subduction Zone Sometimes the molten rock cools down below the surface 12

Continental Collision When two plates carrying continents collide mountain chains are built 13

An Oceanic Ridge If plates are being destroyed, new plate material must be being made somewhere else - At new plate margins 14

Click on the image to launch ‘What Wegener Knew’ PowerPoint What Wegener knew: an example of ‘how science works’ 15

16

17

18

Evidence for the structure of the Earth 19

Launch of a depth charge 20

Earthquake damage 21

22

23

The lithosphere (!) 24

Evidence for plate tectonics 25

Convection in the lab 26

27

Modelling the mantle 28

Mid-Atlantic ridge (Hugo Ahlenius, UNEP/GRID-Arendal) 29

Icelandic-type eruption Reproduced with kind permission of U.S. Department of Interior, U.S. Geological Survey 30

Black Smokers 31

Pillow lavas 32

33

Research ship used to tow magnetometer 34

The equipment used 35

36

Age of the sea floor © Dale S. Sawyer 37

38

39

40

41

Island arc volcanism: Zavadovski Island 42

43

Ocean-continent convergence: Mount St Helens Courtesy of USGS/Cascades Volcano Observatory 44

45

Folds at Lhotse (Himalayas) 46

47

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 48

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 Solid Earth Atmosphere 49

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 Hydrosphere Biosphere 50