How did opponents of continental drift account

Written Assignment – Evolution of North America

Write a one page summary of the tectonic evolution of the region of the North American continent in which you live. Refer to your assigned reading.

Discussion – Future Accretion

Where are today's exotic terranes? What is their fate? Once East Africa has rifted from the African Plate, is it destined to become an accreted terrane? Will it become a new continent? Discuss these issues, based on this week's reading.

Chapter 2 – Reading

2.1 From Continental Drift to Plate Tectonics Summarize the view that most geologists held prior to the 1960s regarding the geographic positions of the ocean basins and continents. Prior to the late 1960s most geologists held the view that the ocean basins and continents had fixed geographic positions and were of great antiquity.

Scientists came to realize that Earth’s continents are not static; instead, they gradually migrate across the globe. These movements cause blocks of continental material to collide, deforming the intervening crust and thereby creating Earth’s great mountain chains (Figure 2.1).

Furthermore, landmasses occasionally split apart. As continental blocks separate, a new ocean basin emerges between them. Meanwhile, other portions of the seafloor plunge into the mantle. In short, a dramatically different model of Earth’s tectonic processes emerged. Tectonic processes def

This profound reversal in scientific thought has been appropriately called a scientific revolution. The revolution began early in the twentieth century as a relatively straightforward proposal termed continental drift. For more than 50 years, the scientific community categorically rejected the idea that continents are capable of

Figure 2.1

The Himalayan mountains where created when the subcontinent of India collided with southeastern Asia. (Photo by Hartmut Postges/Robert Harding) movement. North American geologists in particular had difficulty accepting continental drift, perhaps because much of the supporting evidence had been gathered from Africa, South America, and Australia, continents with which most North American geologists were unfamiliar.

After World War II, modern instruments replaced rock hammers as the tools of choice for many researchers. Armed with more advanced tools, geologists and a new breed of researchers, including geophysicists and geochemists, made several surprising discoveries that rekindled interest in the drift hypothesis. By 1968 these developments had led to the unfolding of a far more encompassing explanation known as the theory of plate tectonics.

In this chapter, we will examine the events that led to this dramatic reversal of scientific opinion. We will also briefly trace the development of the continental drift hypothesis, examine why it was initially rejected, and consider the evidence that finally led to the acceptance of its direct descendant—the theory of plate tectonics.

2.1 Concept Checks Briefly describe the view held by most geologists regarding the ocean basins and continents prior to the 1960s. What group of geologists were the least receptive to the continental drift hypothesis? Why?