4. The idea that the continents are slowly
drifting apart is known as continental
drift.
He published his evidence in a
book called Origin of
Continents and Oceans in 1915.
6. European coal mines matched up
with coal mines in North America.
Original Pangaean Coal Deposits in the "Gray Band"
7. Evidence From Fossils
•A fossil is a trace of an organism
that has been preserved in rock.
• Fossils for Mesosaurus and
Lystrosaurus were found in places
now separated by oceans.
9. Evidence From Fossils
• Another example was
Glossopteris which is a fernlike
plant that lived 250 million
years ago. It was found in rocks
in Africa, Australia, India and Antarctica.
• The seeds of this plant could not have been
carried by the wind and are too fragile to
survive an ocean trip.
10. Evidence From Fossils
• Wegener concluded that fossils of the
reptiles separated by an ocean that they
could not have swum and the widespread
occurrence of the fern’s fossils supported
his hypothesis of continental drift.
11. Evidence From Climate
• Spitsbergen is an island in the
Artic Ocean north of Norway.
• The island is ice-covered with
harsh polar climates.
• Fossils of tropical plants were
found on this island. When these
plants lived 300 million years
ago, the island must have had a
warm and mild climate.
•Wegener concluded that the
island must have been located
near the equator.
12. Evidence From Climate
• Geologists also found evidence
that at the same time it was warmer
in Spitsbergen, it was much colder
in South Africa.
• There is evidence that continental
glaciers once covered South Africa.
•Continental Glaciers are thick
layers of ice that covered
hundreds of thousands of
square kilometers.
•The climate of South Africa today
is too mild to have sustained
continental glaciers.
13. Explanations
• Wegener also attempted to explain how
the drift took place and offer a new
explanation for how mountains form.
• He thought that when the drifting
continents collide, their edges fold or
crumble.
•The folding continents slowly push up
huge chunks of rock to form mountains.
14. Scientists Reject Wegener’s Hypothesis
What forced or pulled the continents
apart?
Wegener thought there were centrifugal
and tidal forces moving the continents, but
had no mechanism to prove it. Other
scientists calculated that these forces could
never be strong enough to move land
masses.
15. Scientists Reject Wegener’s Hypothesis
Geologists would have to reject their own theories of how
mountains form.
The fact that his work crossed disciplines exposed him to the
territoriality of those disciplines. The authorities in the various areas
attacked him as an interloper that did not fully grasp their own
subject. More importantly however, was that even the possibility of
Continental Drift was a huge threat to the established authorities in
each of the disciplines.
One of Alfred Wegener's critics, the geologist R. Thomas
Chamberlain, could not have summarized this threat any better :
"If we are to believe in Wegener's hypothesis we must forget
everything which has been learned in the past 70 years and start all
over again."
16. Scientists Reject Wegener’s Hypothesis
Geologists in the early 1900 thought that the
Earth was cooling and shrinking.
It suggested that the Earth had been in a molten state, and
features such as mountains formed as it cooled and
shrank. As the interior of the Earth cooled and shrank, the
rigid crust would have to shrink and crumple. The
crumpling could produce features such as mountain
ranges.
True geologists were unwilling to believe that the evidence
already collected about mountain formation could be
explained away by an unqualified scientist (Wegener was a
trained astronomer and meteorologist, not geologist).
17. Scientists Reject Wegener’s Hypothesis
• According to this idea, Wegener said the
crust would wrinkle all over the Earth.
• Wegener noted that mountains are formed
in narrow bands along the edges of the
continents.
• Wegener’s theory was rejected until the
1950s when new evidence about the Earth’s
structure caused scientists to reconsider the
hypothesis.
