Building a Theory
Example Plate Tectonics
Text: Chapter 2 with parts of
Chapter 1
Steps on Scientific Method
• 1 Collection of facts based on
observations and measurements
• 2. Develop possible explanations
(hypotheses) (a stories)
– Multiple working hypotheses
• 3. Test hypotheses with additional facts to
get the best explanation (theory)
• 4. Accept, reject, modify theory
Paradigm
• Theory that is held with a very high degree of
confidence and is comprehensive in scope.
• Paradigm Shift – The replacement of an existing
paradigm with a better paradigm.
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Technology provides new information
New facts don’t fit existing paradigm
A major change in understanding
Occurs at decade to century time scale
Tremendous economic opportunity
Observational Facts (1830-1859)
• Continents consist of relatively horizontal
sedimentary rocks and disturbed belts
(mountain ranges).
• Many disturbed belts consist of unusually
thick sequences of sedimentary rocks that
were deposited in shallow water.
• Thick sequences of sedimentary rock or
ocean trenches occur adjacent to
disturbed belts.
Geosynclinal Theory
• Paradigm 1859 – 1969 (110 years)
– Peaked in 1951
• Based on distribution of rock units,
disturbed belts, and mineral resources
• Oldest crust is in continental interiors
– Challenged 1912 – 1930
• Shape of continents
• Paleoclimate data from fossils
• Distributation of some fossils
Ideas and Technologies
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Radiometric age dating
Paleomganetics (Inclination, Declination)
Tectogene (thermal convection of the mantle)
Seismic Model of the Earth
Post WWII geophysics
Map of the sea floor
– Sputnik 1956
• International Geophysics Year 1958
• Project Mohole (1957-1966)
Paleomagnetics
• PALEOMAGNETIC TIMESCALE
Seafloor Paleomganetics
Plate Tectonics
• Major components of the theory were
developed by several independent
researchers (1961-1969).
• J. Tuzo Wilson (Canadian)
–Wilson Cycle
Wilson Cycle
• Continent fragmentation
• Formation of new ocean floors between
continent fragments
• Closing of old ocean basin
• Continent fragments collide to form a new
continent with a new mountain ranges
marking the collisions
Wilson Cycle
• Successive cycles take longer
– Crust becomes thicker
– Crust becomes stronger
– Progressive decline in radiogentic heat
sources
– Progressive decline in geothermal heat
• Present cycle began about 175 million
years ago with the fragmentation of
Pangaea (supercontinent)
Present Wilson Cycle
175 my to Present
Previous Cycle
Assembly of Pangaea
600my to 300 my
• ..\..\Desktop\applachian Orogen.jpg
Features – Hot Spots
Features – Hot Spots
Divergent Boundaries
Convergent Boundaries
• Ocean – Continent
• Ocean – Ocean
• Continent - Continent
Transform
Transform
Present Plate Motions
Assignment
• Chapter 3 Minerals
atomic number
atomic weight
octet rule