Download Development of Plate Tectonics

Continental Drift
By about 1900, advances in geology, biology and geochemistry (primarily
radioactivity)
 Earth is billions of years old.
 Earth is dynamic - The rocks and landforms that we see today evolved over
a very long history, including:
• mountain building
• erosion
• sedimentation
• metamorphism
• etc.
However, until the second half of the 20th century, most models of the
evolution of the Earth involved:
Vertical Tectonics
Very few geologists believed that large scale horizontal motions could occur.
It was thought that the physical properties of Earth materials could not
permit such motions.
Alfred Wegener and Continental Drift
Although several people had proposed continental drift as far back as the
1600’s, such an hypothesis was not generally accepted.
In 1912, a German climatologist named Afred Wegener published a book
entitled Origin of Continents and Oceans in which he proposed an hypothesis
of continental and listed supporting evidence for it.
Wegener’s evidence came from:
Reconstruction of ancient climates
Similar fossils on widely separated continents
Matching rock structures across ocean basins
Geometrical fit of continental margins
Stages in the Development of Plate Tectonics
1912-1915: Continental drift proposed by Alfred Wegener
1915-1930: Continental drift debated
1930-1950: Stalemate
1950-1960: Revival of interest in continental drift
• Paleomagnetism
• Ocean Floor Exploration (Mid-ocean ridges and young age of oceanic crust)
1962: High heat flow over mid-ocean ridges/convection (H. Hess)
1963: Magnetic anomalies parallel to mid-ocean ridges (F. Vine and D. Matthews)
1965: Transform faults and earthquake locations in ocean basins (J.T. Wilson)
1968: Earthquake locations and direction of ground motion associated with earthquakes
consistent with plate motion (J. Oliver, B. Isacks and L. Sykes)
1970-?: Plate tectonics accepted by most geoscientists
Geology and Geophysics
Geology is the science that deals with the
history of the earth as recorded in rocks.
Geophysics is the science that employs methods
of physics and mathematics to explore the
structure and dynamics of the Earth.
“Academic Wannabes”
“Academic
Wannabes”
Great Academic Chain of Being:
Engineers want to be experimental physicists.
Experimental physicists want to be theoretical physicists.
Theoretical physicists want to be mathematicians.
Mathematicians want to be philosophers.
Geophysicists?
Philosophers want to be theologians.
Geologists?
+
Theologians want to be engineers.
- From, James Trefil
Reading the Mind of God: In Search of the Principle of Universality
“The real purpose of the
scientific method is to make
sure that nature hasn’t misled
you into thinking that you know
something that you don’t
actually know.”
Robert M. Pirsig, Zen and the Art of
Motorcycle Maintenance: An Inquiry
into Values
Paleomagnetism
N
N1
N2
Paths of
Apparent Polar
Wandering
N3
N4
Continent
Outcrop
Transform Faults
and Earthquakes
Not Observed
1965 J.T. Wilson
Observed
Wegener’s Dream
"This must be left to the geodesists. I have
no doubt that in the not too distant future
we will be successful in making a precise
measurement of the drift of North America
relative to Europe." -- Alfred Wegener, 1929
Geology, Geophysics, and Geodesy
Geology is the science that deals with the
history of the earth as recorded in rocks.
Geophysics is the science that employs methods
of physics and mathematics to explore the
structure and dynamics of the Earth.
Geodesy is the science of determining the size
and shape of the earth and the precise location
of points on its surface.
Space-Based Geodesy
Using satellite observations: Can measure relative positions of
points on the Earth’s surface with a precision of a a few mm.