Transcript Continental Drift

Building a Theory of Plate Tectonics
• The Theory of Plate Tectonics says that the
Lithosphere is cracked and broken into pieces
called plates that move on top of the
convecting Asthenosphere.
• This motion creates mountains, volcanoes,
trenches and earthquakes on the surface of
the planet.
The Lithosphere is Broken into @ 20
Tectonic Plates
Lithospheric Tectonic Plates
• “Tecton” means “to build”
• Move and interact in three
ways to form 3 boundary
types:
– Convergent- Come together
– Divergent- Separate
– Transform- Slide past each
other
The Theory of Continental Drift
The Theory
of
Continental Drift (1912)
• Continents were together in one
large landmass called Pangea and
began drifting apart 250-300
million years ago (mya).
Alfred Wegener (1880-1930)
Geologic Time Line
Pangea – “All Land
(Early Permian (290 mya to Early Jurassic (200 mya))”
225 Million Years Ago (mya)
• During the Triassic
Period (248-209mya)
the continents were
still together in a large
landmass known as
Pangea and began to
drift apart about 200
(mya).
• The climate was
warm and dry for the
entire supercontinent.
Ginko- “living fossil”
Tree Fern
Horsetail
Conifer Forest
Ferns
Evidence
Supporting the
Continental Drift Theory
1. Jig Saw Puzzle Fit
• The apparent fit of
continental coast lines
was the first clue
Wegener used to
support his theory.
Observe a World Map. Which
continents look like they could
fit together?
2. Fossil Clues
Glossopteris Fossil (Tree Fern)
• Fern fossil found on 5
different continents:
Africa, South America,
Antarctica, Australia and
India.
What is the Significance of
this discovery?
The presence of this fern in
so many areas with widely
different climates led
Wegener to conclude that all
of these areas were one
together and shared a similar
climate.
Mesosaurus Fossil
• Small swimming reptile that
lived in freshwater and about
280 mya. Fossil remains are
found in South America
and Africa.
How could these fossils be found so
far apart?
They couldn’t swim in salt water and
could not swim the distance between
the continents, so Wegener
hypothesized that they lived on both
continents when they were together.
Lystrosaurus Fossil
• Fresh Water Reptile
fossil found in Africa
• and India
• Could not swim in
salt water and could
not swim the distance
between oceans
3. Climate Clues
Warm Weathered Plants
• Fossils of warm
weathered plants
found on island of
Spitzbergen in the
Arctic.
What does this fossil find suggest about
the past climate of Spitzbergen?
Wegener believed that the island drifted
from warm weathered areas.
Glacial Deposits and Glacial Grooving
• Glacial deposits and
grooved bedrock are
found in Southern
areas of South
America, Africa,
India, and Australia.
How could you explain why glacial deposits and grooving were found
in areas where no glaciers existed today?
Wegener thought that these continents were once together near Earth’s
south pole and covered with glaciers
4. Rock Clues
Mountain Ranges Match
• Parts of Appalachian
Mountains are found
in Greenland and
Western Europe.
If the continents were not
connected, then how could
mountain ranges match?
Similar Rock Structures
• Similar rock structures
were found on South
America and Africa.
How do these clues support
the idea that the continents
were once together?
Weakness of Theory
• Wegener could not
explain How or Why
the continents drifted
apart, so his theory
was rejected at the
time.
The Initial Break Up
• About 180 -200 million
years ago the
Supercontinent Pangea
began to break up.
• Laurasia was the Northern
most continent and consisted of
present day North America,
Asia and Europe
• Gondwanaland was the
Southernmost continent and
consisted of South America,
Africa, Antarctica, Australia
and India
• Panthalassa (“all Ocean”)was
the name of the ocean
surrounding Pangea.
Watch the Break up of Pangea.
Pangea Animation
http://educatoral.com/img/pangea_anim.gif
"Pangea Ultima"