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Class
6: Lithosphere
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Visit the following website to obtain both an overview and details
about plate tectonics. This site, "The Story of Plate Tectonics,"
plus the indicated pages in BP, provide very good information and
illustrations on all aspects of plate tectonics. We ask that you
look at the entire site now by pressing the links provided within
each graphic image:
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The
content can be found in the active external links. |
| HISTORICAL
PERSPECTIVE (USGS): The purpose of this website is to
introduce the student to the historical
perspective of how the earth formed. It provides the
multiple paradigms forwarded by geologist’s during the
past few centuries. |
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'Developing the Theory of Plate Tectonics': This excellent
site from the U. S. Geological Survey provides an historical perspective
on development
of the theory. You will also find more information on plate
motions, hotspots, unanswered questions, and people and plate tectonics.
Excellent illustrations and text.
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GEOLOGY- Plate
Tectonics: From the Museum of Paleontology at the University
of California provides animations of the continents changing positions
during geologic time. Go directly to the animations. The animations
showing motion of continents relative to one another are very good.
Also, there are links to concise information about sea floor spreading,
magnetic anomalies on the sea floor, and the historical development
of plate tectonics. From this site you will find animations for
divergent, convergent, and transformational plate tectonics.
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"The Story of Plate Tectonics." (USGS):
It shows divergent (spreading ridge or rift zone), convergent, and
transform plate boundaries as illustrated in the Earth. Press the
link button entitled “Understanding Plate Motions” to
read more information about these types of plate boundaries. Use
this lithospheric
plate motion site to view simple and effective animations
showing how plates move with respect to one-another. As illustrated
in the website, hands may be used to demonstrate the concepts of
plate movement. (please note: Visit the page below only if you
do not recall the different types of plate boundaries.)
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| Question:
What are the essential differences between divergent, convergent,
and transform plate boundaries?
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Do
we know that lithospheric plates are moving today?
Yes, we
now have convincing evidence that the plates are moving! By using
the Global Positioning System(GPS), it is possible to demonstrate
that lithospheric plates move relative to each other, and determine
how far they move each year. GPS consists of a network of 24 satellites,
each in circular orbit 20,200 kilometers above the Earth. These
satellites send signals to GPS receivers on Earth that enable
both the position of the satellite and the distance to the satellite
to be known precisely. By knowing our exact distance from a satellite,
we know we are somewhere on the surface of an imaginary sphere
that has a radius equal to the distance to the satellite. If we
know our exact distance to a second satellite, we then know that
we are located somewhere on a circle that marks the intersection
of two imaginary spheres of known size. With additional satellites
and measurements, it is possible to precisely determine our position
on Earth relative to all other positions. This makes it possible
to determine that the plates move. For example, by determining
the position of a point in North America relative to a point in
Europe, and then checking the positions a year later, it has been
found that the North American plate has moved relative to the
Eurasian plate. This determination is possible because distances
can be measured with a precision of 5 to 10 mm. Thus, it is possible
to detect the small changes in distance associated with the motions
of tectonic plates, displacements associated with earthquakes,
changes in sea level, movement and melting of ice sheets, etc.
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| If you
wish more information about use of GPS in studying Earth processes
and natural hazards, then we suggest that you visit this site (optional)
by pressing the links provided within the graphic image:
This site highlihgts some of the practical applications of GPS.
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| Question:
How is GPS used, or how could it be used, in routine or common activities? |
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