Transcript Lecture 2 - School of Earth and Environment

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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
• Mantle
• composed largely
of peridotite
• dark, dense
igneous rock
• rich in iron and
magnesium
• Core
• iron and a small
amount of nickel
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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
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Earth’s Crust
• Continental
• (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
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Plate Tectonic Theory
• Lithosphere is broken into individual pieces called
plates
• Plates move over the asthenosphere
– as a result of underlying convection cells
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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 Map
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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
Ridge
Transform
Divergent
Cont.-Cont.
Convergent
Cont.-Ocean
Convergent
Ocean-ocean
Convergent
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The upper part of the mantle and the crust
• There are convection cells (currents) in the mantle
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• There are currentsZone
in the mantle
A Subduction
• 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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What Wegener knew: an example of ‘how science
works’
Click on the
image to
launch ‘What
Wegener
Knew’
PowerPoint
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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 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
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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
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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