Transcript Plate Tectonics

Chapter 10:
Plate Tectonics
Section 1: Continental Drift
http://education.sdsc.edu/optiputer/flash/pangea_4.htm
Theory of Continental Drift
• A Dutch cartographer, Ortelius, noted the fit of the
coastlines of Africa and S. America.
• In 1912, Alfred Wegener thought that the shape of the
continents was no coincidence.
• He proposed his idea of continental drift to scientists,
but couldn’t tell them why they formed puzzle-like
pieces.
– He proposed that perhaps the continents were
plowing through the ocean floor, and the movement
was caused by Earth’s spinning on its axis.
• He called the land mass of all lands “Pangaea.”
• It was a very controversial idea at the time.
A Variety of
Animations
http://www.nature.nps.gov/geology/u
sgsnps/animate/pltecan.html
India Slamming into the
Eurasian Continent
http://education.sdsc.edu/optiputer/fla
sh/indiaMove.htm
1. The continents fit
together like
puzzle pieces.
– If you look at the
continental shelves
of continents, they
fit even better.
Evidence
Evidence
2. Fossil clues
– Like fossils
were found
along
continental
boundaries,
supporting
that they had
once been
together.
Evidence—Fossils (continued)
• The fossil of the Glossopteris plant was
found on many continents, even
Antarctica, which gives evidence that
Antarctica had once been at a warmer
latitude than it is now.
• The Mesosaurus reptile fossil was found
in S. America and Africa, supporting the
theory that these two continents were once
connected.
– The Mesosaurus was likely a freshwater reptile.
– It did not have the capability to swim
long distances.
MESOSAURUS
GLOSSOPTERIS
Fossil of extinct Glossopteris tree
Glossopteris as it looked on Pangaea
3. Climate evidence
on various
continents.
– Glacial scratches
and deposits
matched across
continents.
– Evidence of past
glaciers is found in
tropical areas where
no glaciers could
be.
– Fossils of warmweather plants were
found in Arctic and
Antarctic regions.
Evidence
CLIMATE CLUES: Glacial Features
4. Matching rocks and
mountain ranges.
– Rocks types match up on
different continents,
supporting that continents
were together.
– Mountain ranges such as
the Appalachian Mountains
of the eastern U.S. are
similar to those found in
Greenland and western
Europe.
– S. American rocks on the
eastern side match up with
rocks on the western edge
of Africa.
Evidence
Matching
Mountain
Ranges
How could continents drift?
• After Wegener’s death, more clues were
found.
– Modern technology helped with this.
• Google Earth
– Sea floor spreading supports the idea, as
well.
Quick Review
• Wegener’s theory of Continental Drift is
supported today by four main parts:
1. The observation that the continents fit together
like puzzle pieces.
2. The fossils Glossopteris and Mesosaurus are
two fossils that are found on different
continents.
3. Climate clues like glacier tracks and fossils of
plants in Arctic regions support that continents
have moved.
4. Rocks and mountain ranges on different
continents match.
Section 2: Seafloor Spreading
Mapping the Ocean Floor
• Before WWI, the
seafloor was
mapped by sailors
lowering a rope
with a weight until
it hit bottom. The
rope was raised
and measured, and
this was repeated.
Mapping the Ocean Floor
• During WWI, sound
waves were used to
detect submarines.
• This technology was
then transferred to
mapping the ocean
floor
• This is called
SONAR
– Stands for “SOund
NAvigation and
Ranging”
Support for
Wegener, at Last!
• In the early 1960s, American scientist
Harry Hess looked at evidence from
SONAR and suggested that the seafloor
is spreading.
– He said that hot, less dense material below
Earth’s crust rises to the surface at the
mid-ocean ridges, leaks out, cools and
causes the seafloor to spread in both
directions.
How Seafloor Spreading Happens
•
http://www.wwnorton.com/college/geo/egeo/animations/ch2.htm#3
http://www.wwnorton.com/college/geo/egeo/flash/2_5.swf
More on Seafloor Spreading
Clues on the Sea Floor
• In 1968, the research ship Glomar
Challenger gathered rock samples and
determined that the youngest rock was
near the mid ocean ridges and got older
farther away from the ridges.
• Magnetism in these rocks also showed
that the north and south poles switch
places over time.
•
•
http://www.indiana.edu/~g103/plate/magstrip.swf
http://www.youtube.com/watch?v=GyMLlLxbfa4&feature=results_video&playnext=1&
list=PL8319D7A4F1ACA3CE
The Glomar Challenger
Magnetic Time Scale
• Iron particles in magma align to the poles
when it leaks out.
• When the magma cools, the particles are
locked in place, leaving a record of pole
reversals on the ocean floor.
• As new magma leaks out, it pushes the old
magma to the side.
• When the poles switch, the particles do, too.
Magnetic Reversals
•
http://earthguide.ucsd.edu/eoc/teachers/t_tectonics/p_paleomag.html
Recorded on the Ocean Floor
Hydrothermal
Vents
•
•
•
http://www.divediscover.whoi
.edu/vents/video.html
http://videos.howstuffworks.c
om/science-channel/29268100-greatest-discoveries-seafloor-spreading-video.htm
http://www.youtube.com/watc
h?v=f9o5BV1aotM&feature=
fvsr
Earth’s Magnetic Field
Protecting Earth
Section 3:
Theory of Plate Tectonics
• Plate tectonics is a theory that
explains how Earth’s crust and part of
the upper mantle are broken into
sections that move.
• These sections are called plates.
Earth’s
Layers
What’s Earth Made
Of?
http://education.sdsc.edu/optiputer/fla
sh/insideEarth.htm
http://education.sdsc.edu/optiputer/fla
sh/outerLayers.htm
http://education.sdsc.edu/optiputer/fla
sh/generalLayers.htm
What Are Earth’s
Plates Made Of?
• The crust and part of the upper mantle
make up the lithosphere.
• These, together float as plates—or
broken sections of lithosphere—upon
the flexible layer called the
asthenosphere.
Plate Boundaries
• Where plates meet and interact are
plate boundaries.
– Divergent boundaries
– Convergent boundaries
– Transform boundaries
Divergent Boundaries
Major Plate
Boundaries
http://education.sdsc.edu/optiputer/fla
sh/plates2.htm
http://education.sdsc.edu/optiputer/fla
sh/plates3.htm
Different Types of
Boundaries
http://education.sdsc.edu/optiputer/tea
chers/platemovement.html
Convection in the
Earth
http://www.classzone.com/books/eart
h_science/terc/content/visualizations/
es0805/es0805page01.cfm?chapter_n
o=visualization
How Fast Do the Plates Move?