Question

List some of the evidence used by Wegener to support his idea of moving continents.

Short answer

Some of the evidence used by Wegener to support his idea of moving continents includes: 1) the apparent fit of continents, like the west coast of Africa and the east coast of South America; 2) the distribution of similar fossils across different continents; 3) similarities in rock formations and geologic structures on different continents; 4) the presence of glacial deposits and striations across the globe; and 5) paleoclimatic evidence suggesting continents had experienced different climates in the past. This evidence contributed to the development of the modern theory of plate tectonics.

Step-by-step solution

1. Fit of continents

One of the most striking pieces of evidence supporting the idea of moving continents is the apparent fit of the continents with each other, such as the west coast of Africa and the east coast of South America. Wegener noticed that these continents seemed to fit together like puzzle pieces.

2. Fossil distribution

Wegener analyzed the distribution of similar fossils across different continents. He found that certain fossils were only found on specific continents, even though the climate and environmental conditions were similar in other areas. For example, the same plant and animal fossils were found on the east coast of South America and on the west coast of Africa, suggesting that these continents were once connected.

3. Similar rock formations

Wegener also noticed that there were similarities in the rock formations and geologic structures on different continents. For example, there are distinct mountain ranges on the east coast of North America and on the west coast of Europe with the same age and rock types, suggesting that these continents were once joined together.

4. Glacial deposits and striations

Glacial deposits and striations (scratches left by moving glaciers) were found on continents across the globe, even in areas that are currently warm and tropical. This indicated that the continents had once been in different positions, experiencing glacial periods or being closer to the poles.

5. Paleoclimatic evidence

Wegener also used paleoclimatic evidence to support his idea of moving continents. By comparing the evidence of past climates on different continents, he found that continents had experienced different climates in the past, which could only be explained if the continents had been in different positions on the Earth's surface. These pieces of evidence helped Wegener to formulate his theory of continental drift, which ultimately led to the development of the modern theory of plate tectonics.

Key concepts

Fossil Distribution

Fossil distribution plays a crucial role in understanding continental drift. When Alfred Wegener proposed his theory, he noticed an intriguing pattern in fossil records across separated continents. Identical fossils of plants and animals were discovered in distinct geographic locations, particularly in places like the eastern coast of South America and the western coast of Africa. This observation was perplexing because these regions are currently separated by a vast ocean.

The presence of similar fossils in such distant areas suggests that these continents were once joined, allowing for the distribution of identical species across them. For instance, the discovery of the fossilized remains of the reptile Mesosaurus in both South America and Africa supports the theory that these continents were once contiguous. The climates of these regions are now vastly different, strengthening the argument that the continents have drifted apart over time.

Paleoclimatic Evidence

Paleoclimatic evidence refers to the clues about past climates preserved in the geological record. Wegener utilized this type of evidence to support the idea of moving continents. He observed that certain regions on separate continents showed signs of having experienced similar climates in the past.

For example, coal deposits were found in parts of Antarctica that would not support such a lush, warm climate today. This indicates that Antarctica must have been situated closer to the equator in the past, allowing for the growth of dense, tropical vegetation. Such evidence shows that continents have shifted, changing their climate zones drastically over geological time spans. This shifting adds another layer of support to Wegener's hypothesis of continental drift.

Glacial Deposits

The study of glacial deposits offers interesting insights into the movement of continents. Scientists discovered glacial deposits in regions that are currently warm and unfitting for glacial activity, such as India and Africa. Wegener noticed that these deposits were similar across various continents, indicating a past connection and different climatic conditions.

Striations or scratches left by glaciers were also found in unusual locations, pointing towards a shared glacial past. These discoveries suggested that these continents, now far apart and in various climate zones, were once positioned closer to the poles and thus subjected to glaciation. This not only provides evidence for altered continental positions but also enhances the validity of the theory of continental drift.

Rock Formations

Rock formations provided strong evidence to support the concept of moving continents. Wegener observed that certain continents exhibited matching geological features. For example, the mountain ranges in eastern North America closely resemble those found in western Europe in terms of age, structure, and type of rock.

This similarity suggests that these continents were once part of the same landmass, allowing the formation of continuous mountain ranges. When the supercontinent broke apart, these ranges remained as counterparts on separate continents. Such geological similarities across distant lands underscore the past connectivity of continents and lend significant support to the idea of continental drift.

Fit of Continents

The fit of continents is often one of the initial visual indicators supporting Wegener's theory. The coastlines of continents such as Africa and South America appear to fit together like pieces of a jigsaw puzzle. This visual cue prompted further investigation into the possibility that these land masses were once a single, larger landmass.

This "fit" isn't perfect due to erosion and changes in sea level over millions of years, but it is striking enough to suggest a former unity of these continents. Recognizing the puzzling nature of continental outlines helps us understand how the Earth’s crust can shift significantly over time, changing the arrangement of land and seas.