Plate Tectonics
Plate Tectonics is a unifying theory that states that the Earth is composed of lithospheric
crustal plates that move slowly, change size, and interact with one another.
This theory was amalgamated from a variety of studies that began in the early 20th
century and culminated in the 1960s.
Early Players:
Richard Oldham (1858-1936): discovered P Wave Shadow Zones
Inge Lehmann (1888-1993): discovered the S Wave Shadow Zone, including the fact that
the outer core is liquid
Eduard Suess (1831-1914): published internal structure of the Earth, utilizing some of
Oldham’s data
Andrija Mohorovicic (1857-1936): discovered the seismic discontinuity between the
crust and the mantle
Beno Gutenberg (1889-1960): found the CMB to be at 2900 km
The Great Synthesizer: Alfred Wagener (1880-1930)
Book: The Origin of Continents and Oceans (1915)
Found six major pieces of evidence the continents move, hence his theory is known as
Continental Drift. (Figures 19.2-1911)
1) The shape of the continents: they fit together
2) Paleontological Evidence: found matching fossils on several continents
a) Glossopteris: found in rocks of the same age on South America, South Africa,
Australia, India and Antarctica
b) Lystrosaurus: found in rocks of the same age on Africa, India,
also some in Asia and Antarctica
c) Mesosaurus: found in rocks of the same age on South America, South Africa
d) Cynognathus: found in rocks of the same age on South America, South Africa
3) Glacial Evidence: the glaciers appear to originate from the modern-day oceans (which
is impossible)
4) Structure and Rock Type: geologic features end on one continent and reappear on the
other (South America and Africa)
5) Paleoclimate Zones: like today, the old Earth had climate zones.
6) Polar Wandering: ancient poles were in different positions than the present poles.
This can only be explained by:
1) Continents remained still and the poles moved
2) Poles were still and the continents moved
(Reality: they both move)
Wagener’s theory was not accepted. Why?
