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Plate Tectonics
Evolution of the Theory of Continental Drift and the Movement
of Earth’s Plates
Historical Perspective of Plate
Tectonics
 The Theory of Continental Drift was first purposed by
German Scientist Alfred Wegener in 1912.
 This suggested that 250 million years ago the
continents were linked together in a super continent
that was called Pangaea.
Can you see how
these continents
might have fitted
together?
Historical Perspectives of
Plate Tectonics
 Wegener was not the first to suggest that the
continents had moved. As early as 1596 a Dutch
mapmaker Abraham Ortelius stated that he believed
that the Americas had torn away from Europe and
Africa!
 Abraham Ortelius’ World
map! Which was very accurate
for its time!
 1858 Geographer Antonio
Snider-Pellegrini noted and showed how well the
continents could fit together.
Historical Perspective of Plate
Tectonics
 Wegener also believed that the continents had
separated and shifted over time. He just was not sure
how they had done so.
 He suggested that the landmasses had plowed through
the oceans and into each other.
 He based his theory on several pieces of evidence
including the fit of the continents, the occurrences of
unusual geological structures, and the matching of
plant and animal fossils across continents.
Historical Perspective of Plate
Tectonics
 His theory was rejected by other scientists, for some it was
rejected because he could not provide an accurate method
for the movement of the continents.
 South African geologist Alexander Du Toit further
theorized that Pangaea divided into two supercontinents 205
million years ago. Du Toit called the northern supercontinent
Laurasia and the southern one Gondwanaland.
 It would take another roughly 50 years before his theory was
proven, and the method of plate movement was determined.
Super Continents
 As I mentioned earlier Wegner and others proposed
that all the continents today were once joined together
in a super continent called PANGAEA!
More Super Continents
 When Pangaea began to break up it separated into two
distinct continents named by Du Toit as Laurasia and
Gondwanaland.
Movement of Continents
 The continents continue to move to their present
locations.
The Evidence for Continental
Drift
 Wegener and Du Toit both mention the continents fitting together,
the matching of geological structures such as mountain ranges,
and plants and animal fossils. What is a Fossil?
 A Fossil is the evidence in rock of the presence of a plant or
animal from an earlier geological
period they are formed when
replace the materials in
tissues creating a
the stone.
minerals
the bones and
replica embedded in
What Were The Fossils?
 Mesosaurus, a freshwater crocodile-like reptile that lived
during the early Permian (between 286 and 258 million
years ago), are found solely in Southern Africa and Eastern
South America. It would have been physiologically
impossible for Mesosaurus to swim between the continents.
This suggests that South America and Africa were joined
during the Early Permian.
 Cynognathus is an extinct mammal-like reptile. The name
literally means ‘dog jaw’. Cynognathus was as large as a
modern wolf and lived during the early to mid Triassic period
(250 to 240 million years ago). It is found as fossils only in
South Africa and South America.
What Were The Fossils?
 Lystrosaurus, which literally means ‘shovel reptile,’
was dominant on land in the early Triassic, 250 million
years ago. It is thought to have been herbivorous and
grew to approximately one metre in length, with a
stocky build like a pig. Fossils of Lystrosaurus are only
found in Antarctica, India and South Africa.
What Were The Fossils?
 Glossopteris was a woody, seed-bearing shrub or
tree, named after the Greek description of ‘tongue’ – a
description of the shape of the leaves. Some reached
30m tall. It evolved during the Early Permian (299
million years ago) and went on to become the dominant
species throughout the period, not becoming extinct
until the end of the Permian. Fossils are found in
Australia, South Africa, South America, India and
Antarctica.
Recreate Pangaea
 We are going to cut up the continents and using the
fossil, and tectonic evidence, as well as what we can
see about how they might fit to try and recreate
Pangaea.
Discussion Questions
 Which two continents have the most obvious fit of the
coastlines?
 Were the fossil symbols and mountain belts helpful in
deciding where to move the continents?
 Why doesn’t the present shapes of the continents fit
perfectly in to a supercontinent?
 Which fossil occurs on the most landmasses? What
does this suggest about when these particular
continents broke up?
What is Evidence?
 Evidence is something that is presented in support of
an assertion or idea! It can be strong evidence or weak
evidence, depending on how well it proves the idea.
 Scientific evidence can be observations, or
experimental findings just saying something is true, or
not true, with no evidence to back it up is not proof!
 Evidence Worksheet!
2 cm a Year!
 Given the fact that we are still moving at 2 cm a year
how long will it take us to move 10cm?
 100cm?
 1 Km?
Current Theory of Plate
Tectonics
 Harry Hammond Hess published ‘The History of Ocean
Basins' in 1962, in which he outlined a theory that could
explain how the continents could actually drift. This theory
later became known as ‘Sea Floor Spreading'. Become
know as Divergent and Convergent Faults
 John Tuzo Wilson proposed that plates might move over
fixed hotspots in the mantle in 1965 he proposed a third type
of plate boundary that he called Transform faults or
Conservative Plate Boundaries. These faults move past
each other horizontally – San Andreas Fault between North
America and Pacific plates
Current Theory of Plate
Tectonics
 Dan McKenzie in mid 1960’s was working on
convection in the Earth’s mantle at Cambridge
University when he became interested in Continental
Drift Theory he used his knowledge of thermodynamics
to address the problem of how plates move. He
suggested there are two layers in the mantle, each of
which are in motion, controlling the movement and
behavior of the tectonic plates above. ‘The Viscosity of
the Lower Mantle’ was published in 1966.
What’s Your Super Continent?
 Create your own jigsaw puzzle of continents with fossil
evidence and tectonic evidence that will allow your
partner to piece it back together once you break it apart
 Be Creative!
 What would you call your Super Continent?