Geology 101 - Lecture 3
(Brief Outline Only)
I. Earth Properties
- Strong vs weak layers
- Magnetism -
- Core of Earth is like bar magnet
- Reversals of magnetic field
- Offset of magnetic pole with respect to geographic pole
Visit
Introduction to the Earth's Magnetosphere
and also
The Magnetosphere
These are both superb links to NASA-sponsored
educational materials about the Earth's magnetic field.
It has some great pictures and explanations in (sometimes) simple
terms.
- Geothermal gradient - increase of temperature with depth in Earth
II. Plate Tectonics
Check out
USGS Plate Tectonics Page
for a great overview of plate tectonics with excellent images
- Early Ideas - e.g. Alfred Wegener and Continental Drift
- Observations but no ability to test hypothesis
-
The WWII Data Explosion - mapping of the seafloor
Summary and Review of Plate tectonics
World
Seafloor Map
History of Plate Tectonic Theory
- Seafloor spreading hypothesis proposed
- Scientists in the early 1960s proposed the hypothesis of seafloor
spreading to explain the ruggedness of the undersea topography,
the magnetic stripes, and the apparent age progression of the seafloor
(youngest at ridges, oldest far away from ridges)
- Growth of plates, not yet a great mechanism for destruction of plates
- Did this mean that the Earth was expanding?
- Harry H. Hess, a Princeton University geologyist and a Naval
Reserve Rear Admiral (who had collected much of the confusing
seafloor data in the 1940's) and Bob Dietz, part of the U.S.
Coast and Geodetic Survey, proposed the idea that if lithosphere
was being created at the mid-ocean ridges, it must be destroyed
at the trenches
- Modern Plate Tectonic Theory, the mechanism
- Divergent Boundaries
- Convergent Boundaries
- Transform Boundaries
- The Driving Force
- convection in the mantle
- ridge push
- trench pull
- Hotspot volcanoes and their role in plate tectonics
- Theory developed in 1963 by the Canadian geophysicist J. Tuzo
Wilson.
- Volcanoes get progressively older away from permanent hotspot.
They record migration of plate over the hotspot
- The Hawaiian islands are the type example.
