Ch 9.1Continental DriftLecture Outline
More than 300 years ago, mapmakers produced world maps that accurately showed the shapes of continents fit together.
A German scientist, Alfred Wegener, also noticed the similarity between the coastlines on opposite sides of the South Atlantic Ocean.
In 1925, Wegener proposed his radical hypothesis of continental drift.
Wegener’s hypothesis suggested that the continents had once been joined
together.
He called this supercontinent Pangaea, meaning all land.
Wegener also hypothesized that about 200 million years ago Pangaea began
breaking into smaller continents. The continents then drifted slowly to
their present positions.
Evidence for Continental Drift
Matching Fossils
Fossil evidence for continental drift includes several organisms on different landmasses.
- Mesosaurus: Freshwater alligator found on Africa and South American
- Glossopteris: Extinct firm plant found on South America, Southern Africa
and India.
- Lystrosaurus: Land repile found on South America, Southern Africa and India.
- Matching Mountain Ranges: North America, British Isles and Scandinavia.
- Matching Rocks Correlate between Africa and South America.
- Ancient Climates: Glacial Deposits showing between 220 million and 300 million years, ice sheets covered large areas of the southern hemisphere.
Rejection of Wegener’s Hypothesis
The main objection to Wegener’s hypothesis was that he could not describe a mechanism capable of moving the continents.
Wegener proposed that the tidal influence of the Moon was strong enough to give the continents a westward motion.
However, physicists quickly responded that tidal friction great enough to move
The continents would stop the Earth’s rotation.
He also proposed, that the larger and sturdier continents broke through the
Oceanic crust…like ice-breakers.
There is no evidence to support this.
Ch 9.1 Continental DriftLecture Outlinep. 2
It would be years before technology and more research would suggest the Theory of Plate Tectonics in 1967.
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Supplimental: Plate TectonicsLecture
The Theory of Continental Drift
1910, a young German scientist named Alfred Wegener became curious about the relationship of the continents. He formed a hypothesis that Earth’s continents had moved.
Wegener’s hypothesis was that all the continents had once been joined together
In a single landmass and have since drifted apart.
- Wegener named this supercontinent Pangaea, meaning “all lands.”
- Pangaea existed about 300 million years ago.
- This was the time when reptiles and winged insects appeared.
- Great tropical forests, which later formed coal deposits, covered large parts
of the Earth’s surface.
- Over millions of years, Pangaea began to break apart.
- The pieces of Pangaea slowly moved toward their present day locations.
Wegener’s idea that the continents slowly moved over Earth’s became known as continental drift.
Wegener gathered evidence from to support his ideas about continental drift.
He published all his evidence from continental drift in a book called The Origin of Continentsand Oceans, first published in 1915.
- All of the Earth’s land was connected 280 million years ago.
- Atlantic Ocean was formed when the land broke apart
- Ocean floors are made up of very young rock.
- Pangaea—name of the large land mass.
- Fossils—preserved remains or evidence of plants or animal life, usually found in
sedimentary rocks.
Ch 9.1Continental DriftLecture Outlinep.3
** Scientists use evidence from fossils to support Wegener’s Theory **
- Glossopteris – extinct fern seeds were found in South America, Australia, and India
- Fossil remains of two small freshwater reptiles, (Mesosaurus – alligator like) similar to animals were found in both South America and Africa.
- Evidence from rocks – folded mountains in South Africa and South Americamatch up or correlate.
- Glacial Deposits -- on South America, Africa, India, Australia, and Antarctica are similar, may have been deposited by the same large glacier.
- Land Bridges – narrow strips of land or string of islands connecting land masses.
- Deposits of salt, coal and limestone derived from coral reefs have provided further rock evidence of continental drift.
*** In spite of all the evidence from fossils and rocks, some scientists still refused to accept
the theory of continental drift. They were waiting for the answer to the a very important
question: How could the continents plow through hard, solid ocean floor??? ***
Past Drifting
- Pangaea broke into two great continents
Gondwanaland
Laurasia
- Gondwanaland splint into South America, Africa, Australia, India and Antarctica
- Laurasia splits into North America, Europe and Asia.
- India drifted North to Asia.
- Australia drifted from Antarctica.
Future Drifting
- The continents appear to be drifting at a rate of about 1 to 5 centimeters per year.
- In 50 million years????
- South Atlantic and IndianOceanswill get larger, and the Pacific Oceanwill get smaller.
- Africa will drift north causing the Mediterranean Sea to disappear.
- Australia will drift north and may collide with Asia.