Continental Drift Theory

1. Continental drift was a theory that explained how
continents shift position on Earth's surface.

2. Theory of Continental Drift
Proposed by Alfred Wegener in 1912, but not
widely accepted until seafloor spreading was
discovered in 1960.
Wegener
1880-1930

3. Continental drift was Wegener’s theory that all continents
had once been joined together in a single landmass and
have drifted apart since.
Wegener named this supercontinent Pangaea.
Wegener’s theory was rejected by scientists because he
could not explain what force pushes or pulls continents.

4. Evidence to support Continental Drift Theory:
Similar plant and animal fossils on the shores of distant continents
 All land on earth fits together like a jigsaw puzzle.
 Glacier deposits
 Mountain ranges from different continents align and are
composed of the same materials.

5. Wegeners structural evidence
•South America and Africa
fit together like a jigsaw
puzzle in both outline as
well as rock type and
geological structure.

6. Continental Drift: Rock Ages
Even before geochronology, the relative framework of rock
ages showed strong correlation across the Atlantic, as did
mountain ranges of similar age.

7. Wegeners paleontological evidence
Wegener was intrigued by the occurrences of geologic structuresand
of plant and animal fossils found on the matching coastlines of South
America and Africa, which are now separated by the Atlantic Ocean.

8. Animals that lived on Southern Hemisphere continents –but
cannot have crossed OceansCyanognatus
Cyanognatus
Lystrosaurus
Mesosaurus

9. Glossopteris...
The Glossopteridales are an
extinct group of seed
plantsthat arose during the
Permian, but went extinct by
the end of the Triassic Period
(~290-205 MY). The rapid
appearance, expansion, and
relatively quick extinction of
this group, as well as the large
number of species (>70), has
made the group very
important for under-standing
paleobiogeography

10. Wegeners evidence
from distribution of
glacial deposits
The distribution of
Paleozoic glacial deposits
in the southern
hemisphere on today’s
map makes it seem that
the glaciers flowed from
the sea to the land.

11. Other paleoclimatological evidence
Other paleoclimaticevidence includes deposits of coal,
desert sandstone, rock salt, wind-blown sand, gypsum,
and glacial deposits
Glacial deposit
evaporite
Coral reef
coal
Deserts
Ice
movements
desert
tropics
Glacial

12. Continental drift explains the distribution of
lungfishes
–Lungfishes evolved when Pangaea was intact

13. TheRejectionof Continental Drift:
•MostinfluentialearthscientistswerebasedintheNorthernHemisphere
, whereas most of the conclusive data came from the Southern
Hemisphere
•Therewereplausiblealternativeexplanationstothe distribution of fossils
and glacial deposits
•Thegeophysisistscouldnot thinkof a forcestrongenoughto make
continents able to plough through Oceanic crust
•WegenerassignedPangeaa far tooyoungage(Cenozoic)
andpaleontologistsfoundithard to believe that so much continental drift
could have occurred in so short time

14. Continental drift became widely accepted when Dr. Harry Hess
discovered seafloor spreading in 1960. Seafloor Spreading occurs at
divergent plate boundaries which subsequently create mid-ocean
ridges. New oceanic crust is formed through magma rising through the
gap and cooling. As plates move, the new crust gradually moves away
from the ridge. Seafloor spreading helps explain continental drift in the
theory of plate tectonics.
How does

15. How does continental drift work
• Plates collide = convergent boundary
• Plates separate = divergent boundary
• Plates slide past one another horizontally =
transform boundary
• Subduction zone = one plate slides under
another

16. Convergent Boundary/subduction zone
• When both are continental plates, the plates push against each other,
creating mountain ranges. Divergent Boundary
• Plates

17. Divergent Boundary
• Plates separate
New crust is formed at Divergent Boundaries.

18. Transform Boundary
Plates slide past one another horizontally

19. What happens when earthquakes happen in the
ocean?
TSUNAMI wave that brings lots of water to the
continents and causes major flooding!
Subduction Zone
• one plate slides under another
Oceanic trench forms at the subduction zone. Volcanoes may form
along this type of boundary.

20. Driving force of Plate tectonics:
CONVECTION CURRENTS

21. This is a model of sea floor spreading at a divergent
boundary called a mid ocean ridge.

22. Rock does two things when stress is placed on it. It can fold
or fault (break). When plates push against one another,
they form MOUNTAINS.
• Folded Mountains – made when rock is squeezed together
and pushed upward
Fault – broken rock layers resulting from stress

23. Volcanic Mountains form along broken rock layers at
convergent boundaries (continental and oceanic crust)
– molten rock erupts to form new material on earth’s
surface (Ring of Fire)
Nicholas Steno – Law of Superposition
Rock layers on the top layer of sedimentary rock are
younger than the rock layers on the bottoms. Fossils
on the bottom of sedimentary rock are older than
fossils on the top layer.
 James Hutton – Law of Crosscutting
geologic feature that cuts another is younger in age
than the surrounding rock.

24. Section D of rock would be younger than the surrounding
rock.

25. Plate: The Earth’s crust consists of a number of mobile
plates, masses of crust that move independently of
adjacent plates.

26. Tectonics: dealing with structural features of the Earth
(e.g., mountains, ocean basins).
Plate Tectonics: The process that involves the
interaction of moving crustal plates and results in major
structural features of the Earth.
A unifying theory in geology that explains a wide range
of geologic phenomena.

27. What did the modern theory replace?
Diastrophism: early term for all movement
of the Earth’s crust.
Thought to result in the formation of
mountains, ocean basins, etc.
Contracting Earth Theory
• Theory that the Earth contracted or shrank
over geologic time.

28. Shrinking
resulted in a
reduction in the
Earth’s diameter
while the
circumference
remained
unchanged due to
folding and
buckling of the
crust
(diastrophism).

29. How Plates Move

30. CONTINENTAL DRIFT