continental+drift

I. Continental Drift 

A.In Idea Before its Time  Alfred Wegener

a.Evidences

1)The Continental Puzzle



2)Matching Fossils



3)Rock Types and Structures



4)Ancient Climates



B.Rejecting a Hypothesis 

Resistance to Wegener's Hypothesis
Resistance to the hypothesis of continental drift came from two main sources--geophysicists and American geologists. Geophysicists were able to demonstrate that tidal force is far too weak to move continents through a viscous mantle. To accomplish this would require tidal forces so great that the Earth would be torn apart. Without a plausible physical mechanism for continental drift, many people considered the whole idea ridiculous. In 1926, the American Association of Petroleum Geologists (AAPG) held a special symposium on the hypothesis of continental drift. AAPG was and still is one the largest and most influential geological organizations in the world. Nearly every aspect of continental drift was criticized. American geology was held in high regard in the early 20th century, and such overwhelming rejection of continental drift put an end to serious scientific discussion of the idea for the next four decades. It could be argued that AAPG was not an appropriate body to render a decision on Wegener's ideas. Consider the state of petroleum geology at the time. Oil and gas were produced only from land areas; no offshore oil wells were drilled until after World War II. Petroleum geologists were land-based continental geologists; they had no experience, interest, or appreciation for marine geology of the ocean basins. Furthermore, petroleum geology was (and still is) an applied aspect of the profession. The goal is to find oil and gas, not to understand basic principles of earth history and tectonics. AAPG had no economic incentive to consider the possible implications of continental drift. Aside from the apparent bias of the AAPG, several other factors may have contributed to the rejection of Wegener's ideas. These factors often come into play whenever a radical new theory is introduced into a mature scientific discipline. With the view of historical analysis, it seems clear that Wegener and continental drift fit a pattern that has been repeated many times in geology as well as other scientific disciplines. As a discipline matures through time, complacency and authority develop, such that new ideas become increasingly difficult to accept. Those who are trained in the discipline "learn" a body of data, facts, methods, and theories which are taken to be literally true. To suggest otherwise may not be in the best interest of a person's reputation and career. Most practitioners of a discipline, thus, have "closed minds" to anything outside the normal dimensions of their work. This was the situation into which Wegener ventured with his hypothesis of continental drift.  1.A New Theory Emerges
 * 1) **Before his time** -- Wegener's hypothesis moved ahead of confirming evidence too fast. Many previously unrelated observations were combined into a large theoretical jump. This is contrary to the normal progressive, step-by-step development of science.
 * 2) **Youthful outsider** -- Wegener was a man of many talents, but he had no formal training in geology. Thus, he had no credentials. At the same time, he had no preconceived position to defend or prove. At the beginning of the 20th century, no scientist was recognized until at least age 40; Wegener was in his early thirties when he first proposed continental drift.
 * 3) **Scientific inertia** -- Geology could not remake itself overnight. There was a natural resistance to change, to accepting radical new ideas. Geologists had vested interests in their work and were reluctant to admit past misinterpretations of fundamental significance.

Magnetic field helped to prove Wegener's theory. Seafloor Spreading Mid Ocean Ridge Convergent Boundary