Lecture #4: From the Hypothesis of Continental Drift
to the Development of the Theory of Plate Tectonics
(Abbott, pp. 28-32, 51-61)
Birth of the Continental Drift Hypothesis
For years, geographers, explorers and others have noticed the similarity in the shapes of
the continents on maps, in particular how Africa and South America seem to fit into each
other like a puzzle (p. 51; Figure 7.21, p. 176).
proposed the concept of
, where the continents slowly move with
respect to each other over time (Figure 3.14, p. 60). In particular, Wegener reconstructed
(Figure 3.13, p. 59), the 220 million year old supercontinent. The
supercontinent was surrounded by a super ocean,
(p. 58; Figure 3.13, p. 59).
Wegener correctly concluded that Europe, North America, South America, Asia, Africa,
Australia, and Antarctica were once together as Pangaea and that, over the past 220
million years, the supercontinent broke up and formed the Atlantic Ocean (Figure 3.14, p.
Wegener used several pieces of evidence to argue for the existence of Pangaea (p.
Shapes of the continents fitting together.
Mountains in eastern North America (Appalachians), Scotland and northwestern
Africa seemingly being part of the same chain.
Same types of rocks occurring along the coasts of Brazil and western Africa, but
not in the Atlantic.
Fossil distributions (for example, the ancient freshwater reptile
lived in eastern South America and western Africa, but not in North America)
Glacial deposits in India and Brazil suggest that these regions were once farther
away from the equator.
Grooves, similar to those in Figure 11.13 (p. 296) left
from the movement of ancient glaciers also radiate from an ancient South Pole.
Figure 11.25 (p. 297) shows how the continents of southern Pangaea