Transcript Plate Tectonics PPT #1

E.S. Plate
Tectonic Notes

Continental Drift
 Alfred Wegener, in 1912 noticed that the
continental shorelines on either side of
the Atlantic looked like they would fit
together.
 Wegener did not believe this was a
coincidence and developed a hypothesis
called Continental Drift.
Continental Drift


Hypothesis stated that
the continents were
once a part of a single
land mass which he
named Pangaea.
The northern
hemisphere is called
Laurasia and the
southern called
Gondwanaland.
Continental Drift



The large ocean is
called Panthalassa.
Wegener believed that
200 million years ago
Pangaea began to
break apart.
He believed that the
continents drifted to
their present positions
creating mountains.
Evidence supporting
Continental Drift--fossil

Fossils of mesosaurus
had been found in
eastern South America
and western Africa.
Evidence supporting
Continental Drift--Rock


The type of rocks in
western Africa and
eastern Brazil were the
same.
The Caledonian
and Appalachian
Mountains line up
when North America
and Europe are placed
next to each other.
Evidence supporting
Continental Drift--paleoclimate


There is evidence that
there were glaciers in
southern Africa.
Today southern Africa
has tropical climates.
Despite all of this evidence,
continental drift was the laughing
stock in the scientific community
because Wegener could not
describe what would cause the
continents to drift over solid
rock.
New Evidence

Seafloor SpreadingIn 1947 scientists
mapped out the MidAtlantic Ridge --an
undersea mountain
range.
New Evidence


These scientists
discovered that the
ocean floor is
relatively young
compared to the age of
the continental rocks.
The mountain ranges
were found to be
volcanic.
Seafloor Spreading

Harry Hess
hypothesized that
there might be magma
welling up from
beneath this ridge.
This would push rocks
away from the ridge,
making the rocks older
farther away from the
ridge.
Seafloor Spreading


These scientists
needed proof for their
hypothesis to be
accepted.
These ocean rocks
were radiometrically
dated and found to get
older away from the
ridge.
Plate Tectonics


Later, information
about the interior of
the earth was
discovered by
studying earthquake
waves.
We now have a theory
called Plate
Tectonics. (see part 2
for more…)