Chapter 5, Problem 1GST

a)

To determine

The observation that led Alfred Wegener to develop the continental drift hypothesis.

Answer to Problem 1GST

The continental drift hypothesis is developed based on the observation about fit of South America and Africa shorelines along the Atlantic Ocean.

Explanation of Solution

A German meteorologist and geophysicist named Alfred Wegener (1880-1930), in his book called “The origin of Continents and Oceans”, have outlined the theory called the continental drift theory. This theory mainly states that the continents are not stable and they are continuously moving slowly.

According to Wegener, the continents were once joined together as a single supercontinent called Pangaea at the beginning. Later, at about 200 million years ago, which is known as the Mesozoic era in the geological time scale, the supercontinent began to drift apart into small continents.

The similarity that exists between the coastlines on the opposite sides of Atlantic Ocean is the primary evidence for this theory. Later, many evidences, such as distribution of fossils, rock types, and climate patterns proved this theory.

To determine

The reason for the rejection of continental drift hypothesis by majority of the scientific community.

Answer to Problem 1GST

The reasons for the rejection of continental drift hypothesis by majority of the scientific community include the assumption that the gravitational forces of the Moon and Sun are responsible for the movement of continents and the assumption that the larger continents broke through the thinner oceanic crust.

Explanation of Solution

A German meteorologist and geophysicist named Alfred Wegener (1880-1930), in his book called “The origin of Continents and Oceans”, have outlined the theory called the continental drift theory. This theory mainly states that the continents are mobile.

When Wegener’s book was published worldwide, it encountered great criticism. Wegner could not provide the suitable driving force for the movement of continents.

Wegener stated that the gravitational forces of the Moon and Sun which produce the Earth’s tides were also capable of moving the continents. However, the famous physicist, Harold Jeffreys argued that if they were so strong to move continents, they would have stopped the rotation of the planet.

Wegener suggested that the larger continents broke through the thinner oceanic crust, as ice breakers cut through ice. However, there is no standard evidence that such ocean floor is so weak that it could allow the passage of the continents without being deformed.

c)

To determine

Whether Wegener followed the basic principles of scientific inquiry.

Answer to Problem 1GST

Wegener followed the basic principles of scientific inquiry and proposed evidences supporting his theory.

Explanation of Solution

According to Wegener, the continents were once grouped together into a single supercontinent called Pangaea at the beginning. Later, at about 200 million years ago, which is known as the Mesozoic era in the geological time scale, the supercontinent began to drift apart into small continents.

The similarity between the coastlines on the opposite sides of Atlantic Ocean is the initial evidence for this theory. Later, he searched for various evidences that supported his theory. One of the evidences is the distribution of same fossil organisms along the coast of South America and Africa. Mesosaurus is one among the fossils that Wegener had identified.

Wegener offered ancient climates as one of the evidences for the continental drift theory. He suspected that the paleoclimate might support the idea of continental drift theory. By this study, he observed that most of the Southern portion was covered by ice sheets around 300 million years ago where large tropical swamps occurred in several locations of Northern Hemisphere.

Wegner concluded that the southern continents in the supercontinent Pangaea are located near the South Pole. This would have created the polar glacial climate and the northern continents might have been present near the equator, which resulted in the formation of large vegetation. Later, the drift of continents occurred.

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.