Download Chapter 12-1 Earth`s Drifting Continents

Chapter 12-1 Earth’s Drifting Continents.
AKA “The proper way to answer these questions.”
1. Why is the theory of a “land bridge” unlikely?
The theory of a land bridge between South America and Africa is not possible because I know that
continental crust is less dense than oceanic crust, but more dense than water. I also know that things can only
sink when they are denser than the material they are on top of. Therefore, if there was a land bridge between
the two continents, there is no way it could have floated on water or sunk into the oceanic crust beneath it.
2. What is the “Theory of Continental Drift?”
The theory proposed by Alfred Wegner that the continents were once joined together and have since
drifted apart.
3. Why didn’t anyone like Wegner?
People did not like Wegner or his idea of continental drift because:
A. It contradicted many of the existing widely accepted ideas about the evolution of Earth.
B. At that time scientists thought the crust could not move horizontally-continents were fixed in their
positions.
C. Older scientists did not like being told what they thought was wrong, especially by a young scientist,
who was not even a geologist. (He was a meteorologist or “weather scientist.”)
4. Give three reasons why Glossopteris provides good evidence for continental drift. [See (1), (2), & (3).]
Glossopteris provides solid evidence for the theory of Continental Drift. “250 million year old fossils of
the species were found in South Africa, Australia, India, and Antarctica.” However, the seeds of this species
were “too large (1) to have been carried by wind” to these distant lands and “too fragile” (2) to have survived
the oceanic journey. Therefore this suggests that all of these locations must at one time have been closer
together. In addition, the presence of a tropical plant such as Glossopteris in the frozen wastelands of
Antarctica, suggests that Antarctica’s climate must have been much warmer millions of years ago. From what
we know, a change in climate must have resulted from a change in position of the continent.
5. Identify & explain 3 pieces of evidence from “rocks” for continental drift.
A. “An ancient folded mountain chain that stretches across South Africa links up with an equally ancient folded
mountain chain in Argentina.” Therefore, this mountain range must have formed when they were connected.
B. “Coal fields in Brazil line up with coal fields with identical layers in Africa.” Therefore, these coal deposits
must have been continuous layers that formed when they were connected.
C. There is great similarity found between glacial deposits in S. America, Africa, India, Australia, and
Antarctica. Because these deposits have been found in very warm climates, this suggests that these landmasses
were part of a larger landmass near the poles.****
D. Other kinds of deposits- salts, coal, and limestone- also provide evidence for continental drift.
i. Most salt deposits occur between 10 and 35 degrees north and south of the equator, but have been
found as far north as Michigan. Which means Michigan at one point must have been much closer
to the equator
ii. Coal usually forms in warm, swampy climates, yet large deposits have been found in Antarctica
Therefore, Antarctica must have been in a warmer location millions of years ago.
iii. Limestone usually forms in tropical climates, but have been found in western Texas and the
northern, central U.S. Therefore, these regions must have been closer to the equator millions of
years ago.