On January 6, 1912, the German Meteorologist Alfred Wegener presented to the public, in a lecture entitled, “Die Heraushebung der Großformen der Erdrinde (Kontinente und Ozeane) auf geophysikalischer Grundlage“, his hypothesis on continental drift in relation to the former super continent Pangaea.
Wegener didn’t propose something completely new; as he based his idea on earlier observations and suggestions, but in his work he had collected a broad array of evidence and his lectures initiated a fierce discussion in the scientific community.
Who, When and What
Who: Roberto Mantovani
When: 1889 and 1909
What: Italian violinist and Scientist
Theory
- Published a hypothesis based on his observations on the volcanic island of Réunion.
- Cracks forming during volcanic eruptions could separate even large parts of an island, could it then be possible that entire continents split apart?
- Mantovani collected various evidence and published maps to show the shape of the hypothetical former continents.
Why it Failed
He explained the driving force behind the breakup of former large continents by the slow expansion of the earth.
Who: Frank B. Taylor
When: 1908
What: Self-educated geologist
- Proposed that the crust of earth was influenced by tidal forces of the moon and the continents were pulled apart in some regions and pushed together in other regions, forming folds like a carpet.
The involved forces were to weak and his explanation wasn’t deemed plausible
Who: Otto Ampferer
When: 1906
What: Austrian Geologist
- He speculated the Alps were formed by folding of the upper crust, as driving force he proposed magma sinking into the mantle and pulling pieces of crust downwards.
his “Unterströmungstheorie (also Subfluenztheorie)” lacked however a convincing source of energy and couldn’t explain all aspects of the genesis of the Alps, as it implied only pulling and not compressive forces needed to form folds and overthrust faults.
Wegener became interested in the idea of a single continent in 1910, while observing an atlas and noting the coasts of the Africa and South America. Some time later he read a paleontological paper discussing the similarities of terrestrial fossil life forms between separated continents.
Pangaea to Present Day
Wegener collected various published evidence to support his theory of a single continent:
– Like a puzzle also the outlines of continents (especially the continental shelves) seem to fit together.
– There are various geomorphologic and geological similarities along the coasts of South America-Africa and Europe-North America.
– Fossil of land vertebrates and plants can be found on different continents, separated today by large oceans.
– Fossil evidence of ancient climates, today without a recognizable pattern, will form climate zones when the continents are put together.
Wegner considered the prevailing explanation for the patterns in the fossil record as impossible: ancient land bridges that connected continents and habitats (like the Isthmus of Panama today) were composed of light continental granitic crust, such pieces of less dense rocks couldn’t simply sink into the much denser oceanic basalts and disappear without trace.
Wegener hypothesised a continental drift (a catchy phrase adopted mainly by the critics, as Wegener talks more general of “displacement theory“) which was received with mixed feelings. Most geologists regarded it as cherry-picking of anecdotes from literature. However some geologist with field experience, especially in Africa and South-America, became soon convinced of this possibility.
Like Taylor, even Wegener could not explain the forces necessary to move the continents trough the crust. Wegener imagined the continents like gigantic ice floes swimming on and surrounded by the much denser oceanic crust. He proposed gravitational pull, tidal and centrifugal forces, but the English geophysicist Harold Jeffreys demonstrated that these forces are much too weak or if strong enough, had to stop earth’s rotation.
Wegner himself reacted to the critics and tried to respond to them in various editions of his books, however with moderate success. The greatest problem remained the lack of direct evidence for the movements of continents and the needed explanation for the mechanism and the immense energy supply. Most importantly Wegener considered his work as starting point and stimulus for other or even future scientists, a message that wasn’t fully understand at his time.
Wegener died in 1930. His continental drift hypothesis was in many aspects erroneous: not the single continents moving but entire plates of the crust and the driving force apparently coming from within the planet, not from outside. However his most important legacy is to have introduced the idea of moving continents to the scientific community and the public, while decades later this legacy will influence a new kind of theory: Plate Tectonics.
On This Day: Trapped in History 