Download Continental Drift - North Mac Schools

Chapter 4: Plate tectonics
The evidence for the theory of plate tectonics has been accumulating for 400 years.
It is only since the 1960’s that this theory has been generally accepted.
IT STARTED WITH MAPS
1920
1936
4.1
Continental Drift
1880-1930
Alfred Wegener’s observations:
1. The continents fit together
like puzzle pieces
1912
Fossils
2. Fossil specimens from South
America match fossil
specimens in Africa
Rocks & Minerals
3. Minerals, Rocks, and mountain
ranges match between continents
on either side of the Atlantic
Current hypothesis of the time was
“land bridges”.
Glacial debris
4. Glacial debris found in
South America and Africa
Fossils
5. Coal and other fossil evidence of tropical climate was
found in North America, Europe, and Siberia.
Continental Drift
In 1912, he proposed his hypothesis called
Continental Drift
Alfred Wegener named
his super continent
“Pangaea”
He named the
surrounding super ocean
“Panthalassa”
Alfred Wegener’s ideas were not accepted because
he did not have a geologic mechanism!
He died in Greenland, 1930.
30 years after his death, that mechanism was found!
https://www.youtube.com/watch?v=T1-cES1Ekto
Mechanism for Continental Drift
WWII in the Pacific, he tracked the sea bottom using “echo sounder”, a.k.a. sonar
1947 – Expedition to study the Mid-Atlantic Ridge
Evidence:
The rocks on the ocean floor were very young compared to
continental rocks!
• None of the rocks were more than 150 million years old
• Continental rocks are as old as 4 billion years
Hess proposed a hypothesis...
Mid-Atlantic Ridge valley is a rift in the Earth’s crust where
magma from the mantle comes through.
He reasoned the ocean floor was moving away from both
sides of the ridge, being replaced by rising magma.
Princeton
Seafloor Spreading
Harry Hess reasoned that that the ocean
floor moved away from the ridge, and was
replaced by magma.
Robert Dietz named this process
“Seafloor Spreading”
These ideas are both hypotheses.
Rock samples were very young compared to continental rocks!
None more than 150 million years old.
Continental rocks have been found that are 4 billion years old.
https://www.youtube.com/watch?v=GyMLlLxbfa4
https://www.youtube.com/watch?v=sgDM6m0lUGY
Paleomagnetism
Magnetic fields on the ocean bottom are mirror images
1965 – two groups of scientists, working
independently, discovered the reversal in rocks on
land, and the other on the ocean floor.
Here was the scientific evidence that Wegener
needed to verify his hypothesis of continental drift.
https://www.youtube.com/watch?v=WhiF6IqGACo
Continental Drift
100 million years ago:
http://www.youtube.com/watch?v=uGcDed4xVD4