Chapters 5, 6, 13, 14, 21, 22

Section 4 for Hominid evolution

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Earth’s Interior Layers•Crust: • 5-90 km thick• Continental and

oceanic

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• 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 Layers3

• 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

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• (20-90 km thick) • density 2.7 g/cm3

• contains Si, Al• Oceanic • (5-10 km thick)• density 3.0 g/cm3 • composed of basalt

Plate Tectonic Theory

•Lithosphere is broken into individual pieces called plates

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• 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.

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Modern Plate Map7

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

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Plate Tectonic Theory•Types of plate boundaries

Transform

Divergent

Cont.-Cont.Convergent Cont.-Ocean

Convergent

Ocean-oceanConvergent

Ridge

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• There are convection cells (currents) in the mantle

The upper part of the mantle and the crust

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• There are currents in the mantleA Subduction Zone• When the currents in the mantle carry one plate down -• It melts and volcanoes are produced

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

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Continental Collision• When two plates carrying continents collide mountain chains

are built

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An Oceanic Ridge• If plates are being destroyed, new plate material must be being made somewhere

else - • At new plate margins

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Click on the image to launch ‘What Wegener Knew’ PowerPoint

What Wegener knew: an example of ‘how science works’

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Evidence for the structure of the Earth

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Launch of a depth charge

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Earthquake damage

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The lithosphere (!)

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Evidence for plate tectonics

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Convection in the lab

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Modelling the mantle

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Mid-Atlantic ridge

http://maps.grida.no/go/graphic/world-ocean-bathymetric-map(Hugo Ahlenius, UNEP/GRID-Arendal)

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Icelandic-type eruption

Reproduced with kind permission of U.S. Department of Interior, U.S. Geological Survey

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Black Smokers

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Pillow lavas

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Research ship used to tow magnetometer

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The equipment used

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Age of the sea floor

© Dale S. Sawyer http://zephyr.rice.edu/plateboundary/home.html

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Island arc volcanism: Zavadovski Island

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Ocean-continent convergence: Mount St Helens

Courtesy of USGS/Cascades Volcano Observatory

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Folds at Lhotse (Himalayas)

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Plate Tectonic Theoryinfluence 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

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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

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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

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