The Structure of the Earth

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The Structure of the Earth
The planet Earth is comprised of a number of
concentric layers. At the center is the core (a
solid inner core and a liquid outer core).
Surrounding the core is the mantle (similar to
mafic minerals like olivine and the ultramafic
peridotite). The outer most layer is the crust
(comprised of the continental crust and oceanic
crust).
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The Lithosphere
Geologists use the term lithosphere to mean an
outer Earth zone, or shell, of rigid, brittle
rock. It includes not only the crust, but also
the cooler, upper part of the mantle that is
composed of brittle rock. The rigid, brittle
lithosphere rests on top of a soft, plastic
underlayer named the asthenosphere. The
lithospheric shell consists of large pieces
called lithospheric plates.
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The Lithosphere
(a) Idealized cross section of the Earth's crust
and upper mantle. (b) Details of the crust and
mantle at the edge of a continent, including the
types of rocks found there. Also shown are the
lithosphere and asthenosphere.
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Continents and Ocean Basins
The major relief features of the Earth are the
continents and ocean basins.The continental
masses consist of two basic subdivisions (1)
active belts of mountain-making and (2) inactive
regions of old, stable rock.
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Continents and Ocean Basins
Principal mountain arcs, island arcs, and
trenches of the world and the mid-oceanic ridge.
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The Ocean Basin
A typical ocean basin is characterized by a
central ridge structure that divides the basin in
about half. The midoceanic ridge consists of
submarine hills that rise gradually to a rugged
central zone. The continental margins are narrow
zones which separate ocean crust from continental
crust. From the ocean to the land it is comprised
of the continental rise, then the continental
slope, then the continental shelf.
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The Ocean Basin
This block diagram shows an inner wedge of
sediments beneath the continental shelf and an
outer wedge of deep-sea sediments beneath the
continental rise and abyssal plain.
This schematic block diagram shows the main
features of ocean basins. It applies particularly
well to the North and South Atlantic oceans.
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Plate Tectonics
The study of the motion of lithospheric plates
and their interactions at their boundaries is
plate tectonics. Tectonics refers to the breaking
and bending of the entire lithosphere, including
the crust. See movie on plate tectonics in the
geodiscoveries section of your texts website.
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Plate Tectonics
Diagram (a) is greatly exaggerated in vertical
scale, and emphasizes surface and crustal
features. Diagram (b) is drawn to true scale.
Here the actual relationships between
lithospheric plates can be examined, but surface
features are too small to be shown.
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The Lithospheric Plates
The rigid outer lithosphere is divided into a
number of lithospheric plates of various shapes
and sizes. The boundaries also differ according
to whether plates are coming together
(converging), moving apart (spreading) or moving
alongside each other (transform). To explore the
lithospheric plates further, visit the Animated
Globe by clicking the globe icon on the menu bar.
To return to this presentation, click "Previous".
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Tectonic Plate Boundary Relationships

• There are three major kinds of active plate
  boundaries
• Spreading boundaries - New lithosphere is being
  formed by accretion.
• Converging boundaries - Subduction is in
  progress, and lithosphere is being consumed.
• Transform boundaries - Plates are gliding past
  one another on a transform fault.

See movie on tectonic plate boundary
relationships in the geodiscoveries section of
your texts website.
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Continents of the Past
The distribution of continents was very different
in the past than it is today. A single
supercontinent, named Pangea, existed around 250
million years ago. It split up over time, and as
the continents drifted we arrived at todays
pattern of land and sea. See animation on
continental drift/change in the geodiscoveries
section of your texts website.
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