1. Living with a Dynamic Planet
Plate Tectonics
Living with a Dynamic Planet

2. Alfred Wegener: a man before his time
Meteorologist
Research on arctic climates – Greenland
Evidence for past climates preserved in rocks
A super-continent: Pangea
Pangea broke apart 200 million years ago
Continents drifted to their present locations

3. Wegener’s Continental Drift

4. Evidence for Pangea: glaciation

5. Evidence for Pangea: paleontology (fossils)

6. How Science Works: Continental Drift Disputed
Lack of Mechanism – what makes continents move?
Alternate explanations possible
Anti-German sentiments in the U.S.
What are the credentials of Wegener?
Continental Drift largely dismissed until 1960’s

7. Oceanography: a new science and new evidence
Following WW II – a convergence of questions, technology, manpower and money
Defense needs – mapping the seafloor
Anti-submarine technology
GI Bill – a wave of scientists and engineers
Booming postwar economy and support for science

8. A new view of the Seafloor
Completely surprising!
Mountains on the sea floor
Trenches – near some continental edges, near islands

9. More puzzles: Magnetic stripes near the Mid-Ocean Ridges

10. A new hypothesis: Sea-Floor Spreading – Making New Oceanic Lithosphere

11. Continental Drift Revised: the New Global Tectonics
Earth’s lithosphere is made of crust and uppermost mantle
Lithosphere is broken into plates
Plates float on moving asthenosphere (upper mantle)
Plate motion driven by heat in mantle
Plates interact – especially at edges

12. Lithosphere and Asthenosphere

14. Plates
Made of Continental and Oceanic Crust – attached to uppermost part of mantle
Plates move
Plate interactions produce specific features (e.g., mountains, etc.) and processes (e.g., earthquakes)
Motion is also related to heat dissipation and density differentiation

15. Balancing the System
Sea Floor (oceanic lithosphere) is created at MOR (divergence)
Either Earth is expanding (no evidence!) or
Sea Floor must be destroyed somewhere – where plates converge

16. Subduction – destroying sea floor
The sinking of cold, dense, oceanic lithosphere into the asthenoshere, beneath an over-riding plate.
Associated: Trenches, Volcanoes, Mountains, Earthquakes

17. Convergence Brings Continents into Collision – Forming Mountains
Subduction of oceanic lithosphere brings landmasses together
Collision of continents (or continent/island arc)
Due to low densities, neither can subduct
Crash!!

18. TRANSFORM BOUNDARIES – Two Plates Passing
Transform boundaries link other types of plate boundaries:
Transform boundaries allow a single plate edge to have multiple types of interactions w/other plates
Transforms are major Faults – Earthquakes!

19. The Big Picture of Plate Interactions

20. Plate Tectonics Explains:
Formation of Oceans
Formation of Mid-ocean Ridges
Formation of Trenches
Formation of Mountains
Formation of Metamorphic Rocks
Formation of Sedimentary Rocks as mountains erode
Earthquakes: cause and distribution
Volcanos: cause, types and distribution
Formation of Igneous Rocks