The Dynamics of Scientific Knowledge - Mapping Scientific Frontiers: The Quest for Knowledge Visualization - page 13

2. Newtonian mechanics, synthesizing celestial and earth-bound physics, replacing
the cosmological views of Descartes
3. Lavoisier's oxygen theory replacing the phlogiston theory of Stahl
4. Darwin's theory of evolution by natural selection replacing the prevailing view
of divine creation of species
5. Einstein's theory of relativity replacing and absorbing Newtonian physics
6. Quantum theory replacing and absorbing Newtonian physics
7. The geological theory of plate tectonics that established the existence of conti-
nental drift
Thagard's central claim is that it is best to explain the growth of scientific
knowledge in terms of explanation coherence . The power of a new paradigm
must be assessed in terms of its strength in explaining phenomena coherently in
comparison with existing paradigms. He demonstrated how the theory of continental
drift gained its strength in terms of its explanation coherence.
A concept system represents part-of and kind-of relations between conceptual
components at various levels. The continental drift theory is a conceptual revolution
that involved structural changes. The German meteorologist and geophysicist Alfred
Lothar Wegener (1880-1930) was the first to give a complete statement of the
continental drift hypothesis. Early geographers making maps of the South Atlantic
Ocean were probably the first to notice the similarity of the coastlines of South
America and Africa. What would be the most convincing reason to explain the
similarity? Is it possible that the two continents used to be adjacent to each other?
Wegener was impressed with the similarity in the coastlines of eastern South
America and western Africa. He speculated that those lands had once been joined
together. It was not until the early twentieth century, however, that Wegener used the
geography of the Atlantic coastlines, along with geologic and paleontological data,
to suggest that all the continents were once connected in the Late Paleozoic era. He
searched for geological and paleontological evidence that could support his theory.
His search in the literature confirmed that there are indeed many closely related
fossil organisms and similar rock strata on widely separated continents, particularly
between the Americas and Africa. Wegener's continental drift theory won some
support in the following decade, but his explanation of the driving forces behind the
continents' movement was not convincing.
Wegener first presented his theory in 1912 and published it in full in 1915 in his
major work Die Entstehung der Kontinente und Ozeane ( The Origin of Continents
and Oceans ). He proposed that there was a single supercontinent, Pangaea ,some
286-320 million years ago and it was later broke up into the continents we see
today. Other scientists had proposed such a supercontinent but had explained the
appearance of isolated continents as the result of the sinking of large portions of
the supercontinent and the deeply sunken areas became today's Atlantic and Indian
oceans. In contrast, Wegener proposed that Pangaea broke up into pieces and these
pieces moved slowly over long periods of geologic time and that is why they are
now thousands of miles apart. He described this movement as die Verschiebung der
Kontinente , i.e. continental displacement, which is the core of the continental drift
theory.