Continental Drift

1
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.

2
Alfred Wegener and Continental Drift

• Although several people had proposed continental
  drift as far back as the 1600s, 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.
• Wegeners evidence came from
• Reconstruction of ancient climates
• Similar fossils on widely separated continents
• Matching rock structures across ocean basins
• Geometrical fit of continental margins

3
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

4
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.
5
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.
• Philosophers want to be theologians.
• Theologians want to be engineers.
• From, James Trefil
• Reading the Mind of God In Search of the
  Principle of Universality

Geophysicists?
Geologists?
6
The real purpose of the scientific method is to
make sure that nature hasnt misled you into
thinking that you know something that you dont
actually know.
Robert M. Pirsig, Zen and the Art of Motorcycle
Maintenance An Inquiry into Values
7
Paleomagnetism
N
N1
N2
Paths of Apparent Polar Wandering
N3
N4
Outcrop
Continent
8
Transform Faultsand Earthquakes
Not Observed
Observed
1965 J.T. Wilson
9
Wegeners 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
10
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.
11
Space-Based Geodesy
Using satellite observations Can measure
relative positions of points on the Earths
surface with a precision of a a few mm.