Continental drift is the slow movement of continents across the Earth's surface due to tectonic plate motions. Evidence for continental drift includes: the matching coastlines of separated continents; matching fossil, rock, and glacial deposits in separated areas; and paleomagnetic data showing continents were once joined. Alfred Wegener first proposed the continental drift theory in 1915, though it was not widely accepted until the 1960s when seafloor spreading was discovered, providing evidence of plate tectonics and explaining the driving force behind continental drift.

1. Continental Drift

2. Definition
 The very slow movement of the continental plates on the
surface of the Earth due to tectonic activity through
geological time.

3. What is the evidence of Continental Drift?
 Continental Fit
 Some continents such as the Western seaboard of Africa and the
Eastern seaboard of South America seem to fit together as if placed
beside each other.

4. What is the evidence of Continental Drift?
 Geological evidence
 Rocks of the same age and type and displaying
the same formations are found in south-east
Brazil and South Africa.
 The trends of the mountains in the eastern
USA and north-west Europe are similar when
placed in their old positions.
 Similar glacial deposits are found in
Antarctica, South America and India, now
thousands of km apart.
 Striations showing the same orientation when
the continents are reunited, are found in Brazil
and West Africa.
 Striations means a series of ridges, furrows
or linear marks, and is used in several ways

5. What is the evidence of Continental Drift?
 Climatic evidence
 Parts of Antarctica, North America and
the UK all contain coal deposits of
similar age that were formed in
tropical conditions.
 These areas are no longer in tropical
climates which suggests that they have
drifted apart since the Carboniferous
period.
• Glacial Striations (scratches in the
rocks) can be found that match in
Brazil and West Africa
• Glacial deposits are also very similar
in India, South America and in the
Vaal Valley in South Africa
• These landmarks suggest that
although these areas are very far apart
now they once had a very similar
climate

6. What is the evidence of Continental
Drift?
 Biological evidence
 Similar fossil formations are found on either side of the Atlantic.
For example, a reptile called Mesosaurus, is found only in South
America and Southern African sediments.
 These are dated from the Permian age (aprox. 280million years ago).
 Plant remains from the humid swamps that later formed coal
deposits have been found in India and Antarctica.
 Marsupials are found only in Australia because it
drifted away from the main supercontinent before
the predators that wiped them out elsewhere had
migrated there.

8. What is the evidence of Continental
Drift?
 Paleomagnetism
 This is when hot magma rises to the earth's surface and cools, the minerals themselves
become magnetized.
 Rocks formed in different places on the planet are magnetized differently.
 When rock layers were discovered with different magnetism than the original rock, it
points to continental drift.
 The Mid Atlantic Ridge was the first piece of evidence to support Wegener’s Theory.
 2 British Geologists, Vine and Matthews, discovered magnetic stripes or banding
running parallel to the ridge in the 1960s.
 These stripes corresponded to times when the Earth’s magnetic field reversed from
North to South and so on, and iron particles in the erupting magma either side of the
ridge cooled and aligned themselves with the Earth’s polarity at that time.
 These symmetric stripes supported a theory by Hess on sea floor spreading, which we
now know exists at the Ridge. In addition, by studying the stripes rates of spreading
could be calculated.
 This has been further supported by studies of the ages of rocks either side of the ridge.
Rocks closest to the ridge are youngest (up to 10 million years old) and those furthest
away are oldest (over 156 million years old) on both sides of the ridge.

11. Theory of Continental drift
 In 1915, the German geologist and meteorologist Alfred Wegener first proposed
the theory of continental drift, which states that parts of the Earth's crust slowly
drift atop a liquid core. The fossil record supports and gives credence to the
theories of continental drift and plate tectonics.
 Wegener hypothesized that there was a gigantic supercontinent 200 million years
ago, which he named Pangaea, meaning "All-earth".
 Pangaea started to break up into two smaller supercontinents, called Laurasia
and Gondwanaland, during the Jurassic period. By the end of the Cretaceous
period, the continents were separating into land masses that look like our
modern-day continents.
 The theory of continental drift was not accepted for many years. One problem
was that a plausible driving force was missing. And it did not help that Wegener
was not a geologist.
 Other geologists also believed that the evidence that Wegener had provided was
not sufficient.
 It is now accepted that the plates carrying the continents do move across the
Earth's surface; ironically one of the chief outstanding questions is the one
Wegener failed to resolve: what is the nature of the forces propelling the plates?

12. Jigsaw Evidence
 Francis Bacon was one of the first people to note that the
West coast of Africa and Europe seem to have a “jigsaw fit”
with the Eastern seaboard of North and South America.
 Wegner provided more evidence stating that the shape of the
east coast of South America fits the west coast of Africa, like
pieces in a jigsaw puzzle.
 Alfred described how the continents would of fit together
forming a super continent which he named Pangea.
 However Wegener was trained as an astronomer and a
meteorologist therefore many geologists did not think that he
had the right background to judge or make geological
theories. For this reason they dismissed much of his evidence.

13. Fossil Evidence in Support of the Theory
 Eduard Suess was an Austrian geologist who first realized that there had
once been a land bridge connecting South America, Africa, India,
Australia, and Antarctica. He named this large land mass Gondwanaland
(named after a district in India where the fossil plant Glossopteris was
found).
 This was the southern supercontinent formed after Pangaea broke up
during the Jurassic period. Suess based his deductions on the fossil plant
Glossopteris, which is found throughout India, South America, southern
Africa, Australia, and Antarctica.
 Fossils of Mesosaurus (one of the first marine reptiles, even older than
the dinosaurs) were found in both South America and South Africa.
 These finds, plus the study of sedimentation and the fossil plant
Glossopteris in these southern continents led Alexander duToit, a South
African scientist, to bolster the idea of the past existence of a
supercontinent in the southern hemisphere, Eduard Suess's
Gondwanaland.
 This lent further support to A. Wegener's Continental Drift Theory

14. Ocean floor spreading theory
 In the 1960s a Scientist called Harry Hess said that not only were the continents
moving but also the sea floor was moving.
 The conveyer belt motion of the sea floor meant that youngest rocks were found
on the mid-ocean ridges and then get older, further away from the mid-ocean
ridge. This shows that the sea floor is spreading and ultimately moving the
continents to cause the continental drift.
 Hess said that the movement of the sea floor
was to do with the convection currents in the
mantle because the hot magma that rises is
less dense than the cooler magma; this magma
cools are forms new rocks when it reaches the
seas surface and consequently other magma
that rises pulls the sea floor apart moving the continents around. Then at the
plate boundaries the cool rocks sinks and melts from the mantles heat.

15. 2 new supercontinent
 South African geologist Alexander du Toit maps out a
northern super-continent, "Laurasia," to explain coal
deposits, which presumably indicate the remains of
equatorial plants, in the Northern Hemisphere.
 Laurasia formed when Pangea broke up to form 2 smaller
supercontinents.
 The other supercontinent was located
in the southern hemisphere and was
known as Gondwanaland.