(a)
The observations that led Alfred Wegner to develop his hypothesis of continental drift.
(a)
Answer to Problem 1GST
It was observed that the shorelines of South America and Africa along the Atlantic Ocean showed best fit as if in a jigsaw-puzzle. This led Alfred Wegner to frame the continental drift hypothesis.
Explanation of Solution
The theory of continental drift proposed by a German meteorologist and geophysicist in his book, “The origin of Continents and Oceans” dealt with the concept of mobility of continents.
According to Wegener, Earth consisted of a single huge landmass in the beginning, which he named as the supercontinent “Pangea”. It is in the Mesozoic Era that the continents started drifting and migration northwards.
The similarity existed between the coastlines on the opposite sides of Atlantic Ocean served as an initiation for the theory. Later the fossil distribution, lithology, climatic patterns added to the evidences to prove the theory.
(b)
The reason for the rejection of the continental drift hypothesis by most of the scientific community.
(b)
Answer to Problem 1GST
The continental drift theory proposed by Wegner faced objection from the other Earth scientists since he was unable to give a proper and satisfying mechanism to explain the movement of the continents and he incorrectly stated that the hard and huge continents could break through the thinner oceanic crust.
Explanation of Solution
According to Alfred Wegner, the continents were altogether a single landmass before (the Pangea) which broke and drifted away from each other gradually to occupy their current geographical positions. Though there were many evidences like the jigsaw-puzzle fit of continents, glacial evidence and fossil evidence to support his theory, it had limitations also for which it was rejected by the scientific community.
Wegner proposed in his theory that the continents drifted gradually as a result of the effect of tides generated on Earth from the gravitational forces of the Moon and Sun. This was not a justifiable and acceptable mechanism to support the movement of continents and thus was very much objected by the other scientists.
Another limitation of Wegner’s theory was that he suggested that the massive and stronger continents were capable of breaking through the thinner oceanic crust. This seemed to be impossible and hence was also rejected by the Earth scientists.
(c)
Whether Wegner followed the basic principles of scientific inquiry.
(c)
Answer to Problem 1GST
It’s true that Wegner followed the basic principles of scientific inquiry and he had evidences also in support of his proposed theory.
Explanation of Solution
According to Wegener, Earth consisted of a single huge landmass in the beginning which he named as the supercontinent “Pangea”. It is in the Mesozoic Era that the continents started drifting and migration northwards.
The similarity existed between the coastlines on the opposite sides of Atlantic Ocean served as an initiation for the theory. Later various other evidences were brought forward to strengthen the theory. One such evidence is the Mesosaurus fossils found from South America and Africa. Had there been no connection between the South America and Africa during the period of life of the Mesosaurus and also that the organism was capable of journeying through the vast South Atlantic, then their fossils would have been found in a number of landmasses.
Wegener offered ancient climates as one of the evidences for continental drift theory. He suspected that the paleoclimate might support the idea of continental drift theory. By this study, they observed that most of the Southern portion was covered by ice sheets around 300 million years ago whereas there occurred large tropical swamps in several locations of Northern Hemisphere.
According to Wegner, if the continents of South America, Africa, Australia, Antarctica and India are imagined as a single landmass as stated in his theory, they would occupy the Southern Hemisphere almost near the South Pole. This polar condition allows for the glaciation in these continents. Meanwhile, the North America, Europe and Asia takes the equatorial position which helps these continents to develop luxurious tropical swamps that were converted to extensive coal deposits on burial later.
Wegener also identified the presence of same rock types in the Brazil and Africa. He also observed the same age of Appalachian mountain belt and the mountains British Isles and Scandinavia. Hence, Wegener proposed that these mountain chains are nearly continuous belts, which later separated due to drifting.
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Chapter 2 Solutions
Essentials of Geology (13th Edition)
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