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Alfred Wegener, a great SES scientist!
(1880-1930)
Thermodynamics of the Atmosphere (1911)
The Origin of Continents and Oceans
(1915,1929)
Climate and Geological Pre-history (1924)
quantitative fitting of the
shapes of W. Africa and E.
South America
The geology matches
very closely
Proterozoic
orogenic belts
>2000 Ma cratons
North
America,
Greenland, and
Africa can be
tied together
And the southern hemisphere continents
Africa
Madagascar
India
South America
Antarctica
Australia
Late Paleozoic
glaciation
Paleozoic and
Mesozoic mountain
belts
The evidence for continental drift was compelling and well
established during the first half of the 20th Centurybut it was not accepted by many geologists (almost all U.S.
geologists) until the advent of plate tectonics in the late 1960’searly 1970’s!
Why??
Why??
 Wegener was attacked because of his lack of geological
credentials and some of his geophysical theories for the
dynamics of continental drift. The dynamics were wrong, but
the kinematics - “continental drift” - was right.
Why??
 Wegener was attacked because of his lack of geological
credentials and some of his erroneous geophysical theories for the
causes of continental drift. The theories were wrong, but the basic
idea was right.
 The focus of geologists on complex continental geology at
local to regional scales
Why??
 Wegener was attacked because of his lack of geological
credentials and some of his erroneous geophysical theories for the
causes of continental drift. The theories were wrong, but the basic
idea was right.
 The focus of geologists on complex continental geology at local
to regional scales
 The obvious importance in continental geology of vertical
motions, leading to the "fixest" (versus "mobilist") synthesis
that was the reigning theory for much of the first half of the
last century.
Why??
 Wegener was attacked because of his lack of geological
credentials and some of his erroneous geophysical theories for the
causes of continental drift. The theories were wrong, but the basic
idea was right.
The focus of geologists on complex continental geology at local
to regional scales
The obvious importance in continental geology of vertical
motions, leading to the "fixest" (versus "mobilist") synthesis that
was the reigning theory for much of the first half of the last
century.
 the ocean basins: “terra incognita” before WWII
WWII-Cold War explosion of technology and observations
 Marine
exploration - opening the last geographic frontier (from
naval warfare, especially submarine warfare)
• mapping ocean bathymetry and crustal structure
• ocean ridge system
• ocean crust a very uniform in structure:
•a single, well defined geological entity
•contrasts with thickness, complexity, variability of continental
crustal structure
•very thin sedimentary cover: ocean floor is a relatively young
geological feature
• development of marine magnetometers: led to SEAFLOOR
SPREADING
WWII-Cold War explosion of technology and observations
 Isotope geochemistry (from development of atomic bomb)
WWII-Cold War explosion of technology and observations
 Global seismological networks : global earthquake locations
and focal mechanisms - (from nuclear test detection and verification for
Cold War and post-Cold War test ban treaties)
WWII-Cold War explosion of technology and observations
 Digital computers
• enabled realistic modeling of processes and observations
• ability to process, analyse and visualize dense, comprehensive
spatial data sets
WWII-Cold War explosion of
technology and observations
 Marine exploration
 Isotope geochemistry
 Global seismological networks
 Digital computers
Plate tectonics
Revolution
(1962 – 1972)
Simplified view of Earth’s tectonic plates
Plate boundary types
divergent
boundary
convergent
boundary
lithospheric
plate
asthenosphere
Plate boundary types
divergent
boundaries
Transform
fault boundary
lithospheric
plate
asthenosphere
Relative motions across modern plate boundaries (cm/year)
Continental
rifting:
formation of
an ocean
Continental
rifting in the
Middle East:
Red Sea and
Gulf of Aden
Convergent boundary: subduction zones
South American
Andes
island
arc
Age of ocean floor recorded by Seafloor Spreading
seafloor
age, Ma
The key breakthroughs:
• Paleomagnetism
• Seafloor Spreading
• Seismicity, plate
boundaries, and subduction
Plate tectonics
Revolution
Geomagnetism: major key
to Earth’s history
The key breakthroughs:
• Paleomagnetism
• Seafloor Spreading
• Seismicity of plate
boundaries
Plate tectonics
Revolution