(PT) Continental Drift Lesson

Continental Drift 

Alfred WegenerAlfred Wegener, born in 1880, was a meteorologist and explorer. In 1910, he noticed that South America and Africa appeared to fit together like puzzle pieces. He was certainly not the first person to notice this. But he was intrigued by the idea and thought a lot about it. He suggested that the two continents were once joined and then moved apart. He set out to find evidence to support or refute this idea.

View the following brief video clip. As you do so, take notes to assist you in the assessment for this lesson. It will be important to understand the progression from the continental drift theory to the theory of plate tectonics and what evidence exists to support each.

 

Wegener's Evidence

Here is the main evidence that Wegener and his supporters collected for his continental drift hypothesis:

Fit of the Continents

The continents appear to fit together, and not just South America and Africa. If the continental margins are included, the fit is even better.

The following figure shows the evolution of the continents, from the super-continent Pangaea to the way they look now.

Pangaea Transition

Distribution of Fossils

Wegener found fossil evidence that the continents were once joined (Figure below). The same type of plant and animal fossils are found on continents that are now widely separated. These organisms would not have been able to travel across the oceans. So how did the fossils get so far apart?

Fossils of the seed fern Glossopteris are found across all of the southern continents. These seeds are too heavy to be carried across the ocean by wind. Mesosaurus fossils are found in South America and South Africa. Mesosaurus could swim, but only in fresh water. Cynognathus and Lystrosaurus were reptiles that lived on land. Both of these animals were unable to swim at all. Their fossils have been found across South America, Africa, India, and Antarctica.

Wegener thought that all of these organisms must have lived side by side. The lands later moved apart so that the fossils are separated.

 

Wegener's Evidence

  • Fossil Evidence MapContinents seemed to fit together. For example, the west coast of Africa seemed to align with the east coast of South America.
  • Ancient fossils of the same species found in rocks of same age on separate continent.   It was impossible for the ancient animals to travel across oceans due to physical limitations such as weight and lack of ability to swim.
  • Identical rock types and ages found on both sides of the Atlantic ocean
  • Mountain ranges with identical rock type, age, and structure found on opposite sides of the Atlantic Ocean.
  • Grooves and rock deposits left by ancient glaciers are found today on different continents very close to the equator. Glaciers were originally massed together in the South Pole but dispersed as continents moved.
  • Coral reefs and coal-forming swamps are found in tropical and subtropical environments, but ancient coal seams and coral reefs are found in locations where it is much too cold today. So ancient creatures were in warm climate zones and their remains spread to different locations over time.
  • Mountains formed as continents ran into each other, which disproved the hypothesis that Earth was a molten ball and bulked up in spots because not all mountains were the same age.

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