Transcript Continental Drift - Perry Local Schools

Continental Drift
Alfred L. Wegener
Untold tragedies of Continental Drift. .
Alfred L. Wegener Alfred Wegener (1880
1930)
Proposed the Theory of
Continental Drift - that
Earth's continents were
originally one land
mass. Pieces of the
land mass split off and
migrated to form the
continents.
• Since Alfred Wegener's initial theory in 1912,
this concept has now proven that the earth's
crust is composed of large and small sections
called plates.
• These plates are different sizes and shapes
(like pieces of a jigsaw puzzle); but they are
constantly moving. The continents are
separate blobs of rock that "float" on the backs
of some of the plates.
• The continents at one time (about 250 M.Y. ago)
were all part of one supercontinent called
Pangaea.... which has since split into 7 large pieces
that have drifted to their present locations.
• The continents are still drifting as the plates continue
to move.
• How these strange things came to be known and
how seemingly unrelated facts and events fit
together "hand-in-glove" to constitute what we call
plate tectonics this is what makes up the fascinating
history of the earth.
• The possibility that continents could move was
suggested long before anyone could hope to
understand or explain how such a thing might be
able to occur.
• In other words, human knowledge of the forces and
processes that govern Earth were virtually unknown.
It was simply not possible to prove that continents
drifted.
• Since the 1950's, enough information began to be
accumulate for some patterns to start emerging.
Some of these patterns, such as pole reversals and
magnetic stripes, now explain what is called sea
floor spreading.
Evidence for Continental Drift
It just seems to fit
Continental Drift
proposed that the continents were once
compressed into a single Supercontinent
 over time they have drifted apart into their
current distribution
 Wegener's hypothesis lacked a geological
mechanism to explain how the continents
could drift across the earth's surface as he
proposed.

Evidence for Continental Drift
 Fit
of the Continents
 Distribution of Fossils
 Similar sequence of rocks at numerous
locations
 Ancient Climates
 Glaciations
Continental Drift Video Clip
Continental Fit
The continents appear
to fit together like a
puzzle along their
coast lines
 The Supercontinent
was called Pangaea
(all lands)

Pangaea was a supercontinent which existed during the
Permian Period about 225 million years ago
Fossil Distribution



Fossils of the same species
were found on several
different continents
For example, Glossopteris,
a fern, was found on the
continents of South
America, Africa, India, and
Australia.
If the continents are
reassembled into Pangaea,
the distribution of
Glossopteris can be
accounted for over a much
smaller contiguous
geographic area
Rock Sequences/Mountains



Rock sequences in South
America, Africa, India,
Antarctica, and Australia
show remarkable similarities
Wegener proposed that the
rock layers were made when
all the continents were part
of Pangaea
they formed in a smaller
contiguous area that was
later broken and drifted
apart.
Glacier Grooves
Glacier Grooves – Kelly’s Island
Glaciations
•
Ancient Climates

Greenland and Antarctica both
contain fossils of tropical plants
found deep under their ice
covered land.

It is believed that these land
masses were once located closer
to the equator for the tropical
plants to have grown here.
Therefore, these lands must
have moved from the equator
area toward the poles.
Problems with Wegener's Model
of Continental Drift
Some thought that
Dispersion by winds or
ocean
Currents could explain the
Distribution of fossil species
 lack of an adequate
mechanism for moving the
continents.
 Wegener proposed that the
Earth's spin caused the
continents to move
 Wegener's work was largely
unaccepted in the northern
hemisphere

1950’s 1960’s Evidence That
Supports the Movement of the
Plates
 Seafloor
Spreading/Subduction
 Paleomagnetism
 Seismic
Data