1. Continental Drift

2. Early Observations Observations
The map shown in Figure 1 was one of the first maps made depicted in the entire earth. It was made in the 1500’s and was the result of the knowledge gained by Columbus, Magellan, and others throughout the Age of Exploration.
The importance of these maps to this discussion is that it appears that the continents on either side of the Atlantic appear to fit together like puzzle pieces, especially South America and Africa
Figure 1. World map made by the Flemish (Dutch) mapmaker Abraham Ortelius, creator of the first modern atlas.
Map From the 1500’s

3. Theory of Continental Drift
An American geologist named Frank Bursley Taylor first prosed an idea in 1908 that Africa and South America were once joined together and that the crunching together of continents created mountain chains. Although we now know this is correct, Taylor failed to provide sufficient evidence to support his hypothesis so very few people took him serious in America.
However, this idea was picked up in Germany by a meteorologist named Alfred Wegener (figure 2) who used rock, fossil, and climatic evidence to publish a book in 1912 that suggested that all of the landmasses were once joined together in a supercontinent that he named Pangaea.
Figure 2. German meteorologist Alfred Wegener who is developed the theory of Continental Drift.

4. Evidence – Rocks A
In the early 1800’s a Prussian scientist named Alexander von Humboldt traveled extensively throughout the world. He noted that some of the mountain ranges that appeared to stop along the Atlantic coast in South America started again along the coast of Africa. These rocks contained rocks of the same age and sequence of rocks (Figure 3).
Although several other scientists discovered evidence which suggested that the continents were once joined, Wegener compiled all of the evidence and used it to support the first comprehensive theory of continental drift.
He reasoned that just like images on a puzzle match up when the correct pieces are put back together, rocks and other forms of geological evidence should match up when the continental puzzle pieces are reconstructed. B
Figure 3. (A) shows how the same sequence of rocks appear on the coasts of South America and Africa. (B) shows how similar rocks on four different continents appear to all match up when Pangaea is reconstructed.

5. This diagram shows how when Pangaea is reconstructed a long mountain chain is created. The rocks that make up part of the Appalachians are very similar in age and structure to those found in Greenland, the United Kingdom, and the Scandinavian countries.

6. Evidence Fossils
Large amounts of paleontological (fossil) evidence was used to support the theory of continental drift.
Fossils of the same species were found on either side of the Atlantic. These animals clearly didn’t swim 3,000 miles to cross the Atlantic so how did the same species end up on different continents?
It was suggested that land bridges once connected the continents and later fell into the oceans. However, there was no evidence to support this hypothesis. Furthermore, land bridges couldn’t explain how an ancient species of bug-like creatures that lived on the seafloor called trilobites could be found in England and also at the same lived on one side of an island near Newfoundland, Canada but not on the other side. Apparently this animal could survive the 2,000 mile trip but could manage to migrate around a 200-mile island.
Fossils of the same plant, an ancient fern, were also found on South America, Africa, India, Antarctica, and Australia (Figure 4). After looking at the morphology of the seeds of this fern it is clear that these seeds don’t use the wind to spread around so how did they travel to continents that are currently thousands of miles apart from each other?
Wegener’s theory suggested that these species roamed across a vast supercontinent, died and became fossilized, and at a later point these fossils were separated as Pangaea broke apart into the continents we see today.
Figure 4. Map showing the distribution of fossils used to support the theory of continental drift.

7. Evidence – Ancient Climates
Glacial till, striations, and other forms of evidence have been found in lower elevations near the tropics. This evidence suggests that large ice sheets once covered India, southern Africa, Australia, and South America. Based on the striations, it also appeared that the ice came from the oceans and moved onto the land which is not possible.
As Figure 5 shows, when Pangaea is reconstructed it shows that these continents were once further south.
Figure 5. Diagram showing ancient glacial evidence used to support the theory of continental drift.

8. Evidence – Ancient Climates
The discovery of ancient ice sheets in locations that are now tropical and sub-tropical could indicate that global temperatures were once much lower. However, at the same that glaciers covered parts of Africa and India, coal deposits and other tropical fossils have been found in areas that are now far north. In fact, coal has been found in places that are now above the Arctic Circle. Because coal formed in tropical, swamps this supported the theory of continental drift.
Figure 6. Diagram showing distribution of coal deposits and ancient glacial evidence used to support the theory of continental drift.

9. Theory Rejected
Although Wegener supported this theory with a lot of strong empirical evidence, his theory was rejected by geological community.
There are several reasons that could have contributed to this ideas not being accepted. First of all he was a German meteorologist suggesting that primarily American and English geologists were wrong. Although science welcomes and embraces new ideas that are supported with evidence, the people who practice science don’t always do so. It is also important to consider the feelings many Americans and Western Europeans had towards Germans at this time (WWI).
However, the primary reason why the theory of Continental Drift was rejected was because Wegener’s theory didn’t adequately explain what force could be responsible for the movement of the continents. He proposed that the continents were plowing through the ocean floor, like a boat through water. However, there is no evidence to support this idea. As a result, this theory was abandoned and for the most part forgotten. However, in the 1960’s new evidence from the seafloor was discovered and this idea would be rescued from obscurity.