Download Plate Tectonics

Plate Tectonics
Alfred Wegener,
meteorologist,
noticed several things
1. Puzzle like fit of the continents
South
America and
Africa
2. Matching fossils
a. Glossopteris flora--seed fern found
in Africa, South America, plus
Antarctica, India, etc. These areas now
have widely different climates
b. Mesosaurus—found in Africa and
South America
These fossils allow for
correlation between the
carboniferous deposits of
southern Brazil and the
record in Argentina,
South Africa, India,
Australia and
Antarctica
3. Ice sheets left marks—
Glacial striations
Scratch marks in the rock that
indicate the direction of movement
of the glaciers

Wegener said that the
continents were once joined and
called the landmass Pangaea
Wegener was
laughed at
because he lacked
a convincing
mechanism for
how the
continents move
continental drift
 His
original
idea of
movement
was that the
continents
plowed
through the
oceans. It was
called
Then the war came
and
they started
mapping the
ocean floor
They found a
mountain chain
in the middle of
the ocean
sea floor spreading
 Herman
Hess came
up with the idea of
sea floor spreading
 Hess said mountains
are located above
upwelling convection
currents in the
mantle
Sea Floor Spreading
As new material oozes up, new
lithosphere is formed. New material takes
on the current orientation of the magnetic
field.
Glomar Challenger—mapped the
ocean floor
Mapping the ocean floor also found
alternating magnetic stripes
that parallel each other
So . . . is the Earth
getting bigger?
NO . . . . . . . .
subduction zones
 New
material is
made at spreading
centers (midoceanic ridges)
and is destroyed
at subduction
zones
The Earth isn’t getting bigger
the crust is being recycled
New crust is made at
spreading centers and old
crust is destroyed at
subduction zones
Accretionary Wedges
 When
crust is
destroyed at
trenches the built up
sediments riding on
the crust are dragged
along
 This stuff is called
an accretionary
wedge
Accretionary mountains
This evidence gave a mechanism for
movement to WEGENER’S IDEA that
the continents were once joined in a
continent called Pangaea!
Theory of
Plate Tectonics
This is BIG!!!
The lithosphere is divided into 8
major plates and several minor ones
that travel along atop the plastic
asthenosphere carried by
convection currents.
The plates ride on the convection
currents
Hot material is less dense
and rises
 As it rises it cools
 The cooled materials sink


CONVECTION
CURRENTS
You will be asked to list some plate names.
Continental
Drift
through time
More evidence
Rock type and structural similarities
Rocks in
northwestern Africa
match those of
eastern Brazil.
 The Appalachian
mountains match
mountains in
northern Europe just
as rock type and
structure on a recent
spreading center,
the Red Sea, match
perfectly on either
side
