4.1.2. Force for Drifting

Wegener suggested that the movement responsible for the drifting of the continents was caused by pole-fleeing force and tidal force. The polar-fleeing force relates to the rotation of the earth. You are aware of the fact that the earth is not a perfect sphere; it has a bulge at the equator. This bulge is due to the rotation of the earth. The second force that was suggested by Wegener — the tidal force — is due to the attraction of the moon and the sun that develops tides in oceanic waters. Wegener believed that these forces would become effective when applied over many million years. However, most scholars considered these forces to be totally inadequate.

Wegener introduced two main forces that he believed caused the continents to drift: the polar-fleeing force and the tidal force. The polar-fleeing force is a result of the Earth's rotation, which causes a slight bulge at the equator. This means that as the Earth spins, there is a tendency for objects at the equator, including the continents, to move outward. The tidal force, on the other hand, is caused by the gravitational pull of the moon and sun, which creates tides in the ocean. Wegener thought that over millions of years, these forces would be strong enough to push the continents apart. However, many scientists during Wegener’s time disagreed and believed that these forces were too weak to bring about such significant movement.

Think of the Earth as a spinning basketball. As it spins, the rubber surface bulges at the equator, similar to how we have the polar-fleeing force. Now, imagine if there were two people (the moon and sun) pulling on the basketball with strings. They can create small shifts, like tides in real water, but they don't have enough strength to move the entire basketball; similarly, during Wegener's time, scientists felt these forces were not sufficient to move continents.

It is interesting to note that for continental drift, most of the evidence was collected from the continental areas in the form of distribution of flora and fauna or deposits, like tillite. A number of discoveries during the post–World War II period added new information to geological literature. Particularly, the information collected from the ocean floor mapping provided new dimensions for the study of distribution of oceans and continents.

After Wegener proposed his theory of continental drift, most evidence relied on observations from land areas, such as the distribution of plants and fossils. However, following World War II, scientists discovered a wealth of new information through ocean floor mapping. This new evidence changed the way geologists understood how continents and oceans interact. They could now see the physical features of the ocean bed, which provided insights into how continents moved apart and formed over time.

Imagine trying to understand a story only by reading chapters from a book without looking at the illustrations. Now, if someone showed you a detailed map or graphic from the book, it would clarify a lot more about the storyline. Similarly, ocean floor mapping gave scientists a clearer picture of Earth's geological history, enabling them to understand the movement of continents in a more informed way.

Arthur Holmes in 1930s discussed the possibility of convection currents operating in the mantle portion. These currents are generated due to radioactive elements causing thermal differences in the mantle portion. Holmes argued that there exists a system of such currents in the entire mantle portion. This was an attempt to provide an explanation to the issue of force, on the basis of which contemporary scientists discarded the continental drift theory.

Arthur Holmes proposed the idea that convection currents within the Earth's mantle were responsible for the movement of continents. These currents are caused by heat generated from radioactive elements that create thermal differences within the mantle. Hot material rises toward the surface, while cooler material sinks down, creating a cycle known as convection. This theory offered a more dynamic explanation for continental movement than Wegener's original ideas, leading scientists to question the adequacy of the continental drift theory.

Think of a boiling pot of water on the stove. The heat from the burner warms the water at the bottom, causing it to rise. As the hot water reaches the top, it cools and then sinks again, creating a cycle. This behavior in the water is similar to the convection currents in the Earth's mantle, which can move the tectonic plates and, thus, the continents above.

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