1) Early scientists like Bacon and Snider-Pellegrini noticed similarities between continents like Africa and South America, but it was Wegener who first proposed the theory of continental drift in 1915. 2) Evidence for continental drift includes matching coastlines, similarities in fossils found on different continents, matching rock types along coastlines, and geological features lining up across continents. 3) In the mid-20th century, discoveries of seafloor spreading and plate tectonics provided the mechanism of plate tectonics to explain continental drift, with ocean floors being created at mid-ocean ridges and spreading outward over time.

3. Continental Drift
Theory

4. Formation of the Theory
Francis Bacon
•In the mid-1600s Bacon
noticed that there’s an odd
puzzle piece fit between
Africa and South America

6. Antonio Snider-Pellegrini
In 1858 Antonio enhanced
Bacon’s discovery by
comparing the coastlines of
Africa and South America
but it was still rejected by
most people
Formation of the Theory

8. Alfred Wegener
• In 1915 he suggested that the fit
between Africa and South America
was due to Continental Drift.

9. Continental Drift
- proposed that continents were once joined together in a single land mass called
Pangaea or the supercontinent

13. Evidences of Continental

14. 1. Fit Of The Continents
•Shelf Break- edge of each
continent
•Coastlines of South
America and Africa and
North America and Europe

17. 2. Similarity of fossils in
different continents
•Fossils- traces and remains
of organisms that lived in
prehistoric times

18. Similarity of fossils in different
continents
•Mesosaurus
-found along the coastlines
of Africa and South
America. The distribution
species were limited to
those places only.
of

19. of

22. •Fossil remains of the
half meter-long fresh or
brackish water (reptile)
Mesosaurus.

23. •Mesosaurs flourished
in the early Mesozoic
Era, about 240 million
years ago.

24. •Mesosaurs had limbs for
swimming, but could also
walk on land. Other fossil
evidence found in rocks
along with Mesosaurs
indicate that they lived in
lakes and coastal bays or
estuaries

25. •Glossopteris
- a fernlike
plant which
thrives in
subpolar
climate

27. Lystrosaurus
EuropeanFlora
Mesosaurus
Glossopteris
Cynognathus

28. •By about 300 million years
ago, a unique community
of plants had evolved
known as the European
flora. Fossils of these
plants are found in Europe
and other areas

29. •3. Similarity of rock type &
age along the matching
coastlines Close match
between rocks in
northwestern coast of
Africa and Eastern Brazil,
South America

30. 4. The continuity of
geologic features from
continent to continent
•Mountain ranges line up
along the matching
coastlines.

32. 5. Presence of coal seams in
Antarctica
•Coal- formed from
organic matter such as
dead plants and
animals.

37. 5. Presence of coal seams in
Antarctica
•Antarctica was once
inhabited by a lot of
organisms.
•Antarctica was once
closer to the equator.

41. 6. Tillites
- deposits of rock debris left
by glaciers
Tillites of the same age
were found in Africa, South
America, India, & Australia

47. If continents drift is
true, what is
making them move

48. Theory was Rejected
•Wegener could not present/
explain the mechanism of
continental drift.

49. Sea Floor Discoveries
WW II: Military Spending

50. U.S. Navy mapped seafloor
with sonar in order to help
ships and submarines
navigate. They expected to
find that the ocean floor
was a vast, flat plain. What
they found was shocking.

51. Sea Floor Discoveries
Instead of miles and miles
of flat surface, they found
that the ocean floor had:

52. oceanic ridges -
submerged mountain
ranges fracture zones -
cracks perpendicular to

53. ridge trenches - narrow,
deep gashes
seamounts - drowned
undersea islands

54. oceanic ridges -
submerged mountain

55. oceanic ridges -
submerged mountain

56. In addition, they
discovered that the rocks
of the seafloor included
only basalt, gabbro, and
serpentinite - no
continental materials.

57. This suggested that the
sea floor was not simply
“covered up” continental
crust, but was made of
different materials and at a
different time

59. The sea floor’s youngest
rocks were located right at
the ocean ridge – and as
you moved away from the
ridge in either direction, the
rocks got progressively
older.

60. The youngest rocks were
created from magma
rising to the surface,
hardening & pushing aside
the older rock. Scientists
called this process “sea
floor spreading.”

61. So now we know:
sea floor is being created
at the mid-ocean ridges
sea floor is spreading
the oldest ocean floor
occurs at the coastlines
of continents…

62. Sea Floor Discoveries
•The ocean floor is pushed
against the continental
crust – and because it is
denser, it dives under the
crust.

63. Sea Floor Discoveries
•The ocean floor is pushed
against the continental
crust – and because it is
denser, it dives under the
crust.

64. Sea Floor
Discoveries
•This process is called
subduction

65. The Rise of Plate Tectonics

66. The Rise of Plate Tectonics

67. •The discovery of these
bands led scientists to
understand that the earth’s
outer shell is broken into
thin, curved plates that
move laterally atop a
weaker underlying layer.

68. Types of Plate Boundaries
•The interaction of the
plate edges with each
other can be classified as
one of three main types
of boundaries:

69. Types of Plate Boundaries
•Convergent boundaries
•Divergent boundaries
•Transform boundaries

70. Types of Plate Boundaries
•Convergent: areas of
plates that are moving
toward each other

71. Oceanic/Oceanic
Convergent Boundaries

73. Oceanic/Continental
Convergent Boundaries

75. Continental /Continental
Convergent Boundaries

77. Types of Plate Boundaries
•Divergent: areas of plates
that are moving away from
each other

79. Types of Plate Boundaries
•Transform: areas of
plates that are sliding
past each other

80. Types of Plate Boundaries

81. Types of Plate Boundaries