1. Definition of ‘Plate Tectonics’
Plate(s) – “flat” pieces of the lithosphere that cover the dynamic earth
Tecton – Greek word for ‘movement’
Plate Tectonics – The study of movement, creation, and destruction of lithospheric (crustal) plates
Dynamic – constantly changing

2. Continental Drift Theory
Alfred Wegener (meteorologist), 1912
Claimed that the continents were once connected into one huge continent called Pangaea (means all lands)
Scientists rejected Wegener’s theory because he could not prove WHY or HOW the continents moved.

3. Alfred Wegener’s Evidence
Evidence I
Evidence II
First Clues
Evidence III
Evidence IV

4. Alfred Wegener (cont.) First clue:
Continents seem to ‘fit together’ (South America & Africa)

5. Alfred Wegener (cont.) original drawings from Wegener’s book “Origin of the Continents and Oceans”

6. Evidence I – Fossil Clues
Fossils found on continents thousands of miles apart: Mesosaurus and Glossopteris

9. Evidence II - Glaciers
Glacial deposits and striations in tropical areas

11. Evidence III – Mountain Ranges
Mountain ranges of same geology (rocks) separated by oceans.
For example: the Appalachian & the Caledonian Mountains

12. Evidence IV Mineral and Rock Deposits
(Other Paleoclimate indicators):
Coal deposits in North America and Europe (and artic areas)
Coral reefs in Northern Canada
Vast sand dunes (desert indicators) not in latitudes associated with deserts.

14. Alfred Wegener (cont.)
Wegener died on a meteorological expedition in Greenland in 1930; his theory still unaccepted.
Would you have accepted or rejected his theory?

15. Sea Floor Spreading Harry Hess
Professor of Geology at Princeton University
World War II broke out, while on active duty as a navy sea captain, he took “soundings” of the ocean floor topography and found the Mid-Atlantic Ridge system.
Continuing his research after the war, Hess speculated that the sea floor was spreading out from vents in the cracks where hot magma oozed up to the surface.

16. Sea Floor Spreading
Theory developed that magma from the Earth’s mantle rises to the surface at the mid-ocean ridge and cools to form new seafloor – like a conveyor belt

17. Evidence
Rock Age – rocks are youngest at the ridge, and they get older as you move away from the ridge / toward the continents
Magnetic Clues – iron minerals in rocks, like basalt, align themselves with the magnetic north pole at the time they crystallize.

18. Sea Floor Spreading
Ridges had high heat flow and universal volcanism throughout
New magma slowly pushes away from the Ridge, causing separation of the ocean floor.
(not in notes)

19. Sea Floor Spreading

20. Sea Floor Spreading
the Mid-Ocean Ridge is the longest mountain chain in the world:
nearly 46,000 miles long in total
undersea mountains more than 12,000 feet high & 1,200 miles wide

21. Sea Floor Spreading Paleomagnetism
Study of the intensity and orientation of the earth's magnetic field
Magnetic orientation is ‘frozen’ in metal bearing igneous rocks

22. Sea Floor Spreading (In 1963, Fred Vine & Drummond Matthews)
Discovered that throughout geologic time, the polarity of the Earths Magnetic field has been reversed
This reversal has been recorded in the rocks on either side of the mid-ocean ridges