In the beginning of 20th century scientist realized that they could not explain many of the earth structure and processes with in a single theory. Many hypotheses developed to try and support the confliction observation

1. Presented To:
7th semester (Morning)
Presented By:
Shah Naseer
Roll #57
Presentation topic:
Outline of various tectonic theories

2. Introduction :
In the beginning of 20th century scientist realized that they could not explain many of
the earth structure and processes with in a single theory. Many hypotheses
developed to try and support the confliction observation

3. Theory
 A theory is a set of accepted beliefs or
principles that explain and guide analysis and
one of the ways that theory is defined is that it
different from practice, when certain principles
are tested. This word is a noun and comes from
the Greek theoria, which means "contemplation
or speculation."

4. Tectonic Theories
 continental drift theory
 sea floor spreading
 plate tectonic theory
 tetrahedral theory

5.  Wegener’s hypothesis
 In 1915, Wegener thought that the
continents we know today had
once been part of an earlier
supercontinent. He called this
great landmass Pangaea (Greek
for “all land”). According to
continental drift, Pangaea broke
apart and the pieces moved to
their present places, becoming
today’s continents.

6.  Evidence for continental drift theory
 Jigsaw Puzzle
It looks like the continents should
 Fossil Record/Climate Shifts
 Coral reefs in the Himalayas
 Age/composition of rocks
 similar age/composition across continents
 Apparent Polar Wandering
 Magnetic anomalies suggest continents moved around

9. Continental drift was rejected
 Continental drift was a good hypothesis that was rejected by other
scientists. A key part of Wegener’s hypothesis was that some
unknown force had caused the continents to slide over, or push
through, the rocky bottoms of the oceans. Yet, neither he nor
anyone else could identify the source of the force needed to move
continents. Continental drift helped explain issues in geology—like
why South America and Africa seem to fit to gather. However,
continental drift could not be accepted by scientists because there
was no evidence to explain how continents could move.

10. The sea-floor spreading hypothesis
 A hypothesis is born
 Hess believed that at Wegener was partly right. The continents had separated from a
supercontinent, but not by flowing through the sea floor. Instead, continents moved along as
part of to growing sea floor! Hess called his hypothesis sea-floor spreading.
 Although his idea seemed to fit with existing observations, Hess realized that he didn’t have
enough supporting evidence for such a breath-taking idea.

11. evidence

12.  Evidence From Magnetic Stripes
 When scientists studied patterns in the rocks of the ocean floor, they found more
support for sea-floor spreading. You read earlier that Earth behaves like a giant
magnet, with a north pole and a south pole. Surprisingly, Earth’s magnetic poles
have reversed themselves many times during Earth’s history. The last reversal
happened 780,000 years ago..
FIGURE Magnetic Stripes Magnetic stripes in the rock of the
ocean floor show the direction of Earth’s magnetic field at the time
the rock hardened.

13.  Evidence From Drilling Samples
 The final proof of sea-floor spreading came from rock samples
obtained by drilling into the ocean floor. The Glomar Challenger, a
drilling ship built in 1968, gathered the samples. The Glomar
Challenger sent drilling pipes through water six kilometers deep to
drill holes in the ocean floor. This feat has been compared to using a
sharp-ended wire to dig a hole into a sidewalk from the top of the
Empire State Building.
FIGURE Sea-Floor Drilling The Glomar Challenger was the first research ship desi

14.  Evidence From Molten Material
 In the 1960s, scientists found evidence that new material is indeed erupting along
mid-ocean ridges. The scientists dived to the ocean floor in Alvin, a small
submarine built to withstand the crushing pressures four kilometers down in the
ocean. In a ridge’s central valley, Alvin’s crew found strange rocks shaped like
pillows or like toothpaste squeezed from a tube. Such rocks form only when
molten material hardens quickly after erupting under water. These rocks showed
that molten material has erupted again and again along the mid-ocean ridge.

15. Plate Tectonic Theory
Proposed by:
 The theory of plate tectonics--formulated by American,
Canadian, and British geophysicists--attributes
earthquakes, volcanoes, the mountain building process,
and related geophysical phenomena to movement and
interaction of the rigid plates forming the earth's crust.

16. According to plate tectonic theory
 , the earth's surface layer, or lithosphere, consists of seven large and 18 smaller plates that move
and interact in various ways. Along their boundaries, they converge, diverge, and slip past one
another, creating the earth's seismic and volcanic activities. These plates at top a layer of partly
molten rock called the asthenosphere. The plates can carry both continents and oceans, or
exclusively one or the other. The Pacific Plate, for example, is entirely oceanic

17. Plate Tectonics
Plate Tectonics – Lithosphere broken into plates move Boundaries
between plates are sites of geologic activity
As plates float on the deformable
asthenosphere, they interact among
each other. The result of these
interactions is the existence of 3
types of boundaries:
• Divergent: plates move away from each
other, examples:
* Divergent oceanic the Mid-Atlantic Ridge
* Divergent continental crust:
the Rift Valley of East Africa
(b) Convergent: plates move toward each
other.
Three possible combinations:
continent-ocean, ocean-ocean,
continent-continent
(c) Transform:
neither (a) nor (b), plates slide
past one another – transform faults.
* Example: San Andreas fault

18. Types of Collisions
 Continent-Continent Collision
When two continental plates collide neither plate can be sub ducted due to their high
buoyancy. With this type of collision there are no features such as a subduction
zone, trench or accretionary wedge. The collision of two continental plates occurs
when a sea becomes narrower until both plates collide. After collision the oceanic
lithosphere breaks off and sinks into the mantle

19.  Ocean-Ocean Collisions
 When two oceanic plates collide one oceanic plate is eventually sub
ducted under the other. Where one plate slides under the other is referred
to as the 'subduction zone'. As the sub ducting plate descends into the
mantle where it is being gradually heated a Benioff zone is formed. This
Benioff zone is a zone of shallow, intermediate and deep focused
earthquakes

20.  Ocean-Continent Collisions
 When an oceanic and a continental plate collide, eventually the oceanic plate is
sub ducted under the continental plate due to the high density of the oceanic
plate. Once again a Benioff zone forms where there are shallow intermediate and
deep focus earthquakes. As the oceanic plate is sub ducted sediment is scraped
off to form an accretionary wedge at the point of collision between the two plates

22. Tetrahedral theory
history
 The theory was first proposed by William Lowthian Green in 1875. It was still popular in 1917
when summarized as:

 According to Tetrahedral theory
 This is
suggesting that a cooling spherical Earth might have shrunk to form a tetrahedron, with its
vertices and edges forming the continents, and four oceans (Pacific Ocean Atlantic
Ocean Indian Ocean and Arctic Ocean) on its faces.
