1. Continental Drift and Plate Tectonics

2. History of Continental Drift
In German "die Verschiebung der Kontinente"
As long as 400 years ago, map makers noted that the continents’ shapes looked to fit together like a puzzle.
LOOK!
Cartographer Abraham Ortelius in his work Thesaurus Geographicus ... suggested that the Americas were "torn away from Europe and Africa ... by earthquakes and floods"

3. The Completed Puzzle

4. Theory of Continental Drift
1912: Alfred Wegener proposed that continents move!
Reaction by the scientific community-
HAHAHAHAHAHA. ROFL - ARE YOU KIDDING?

5. Why did Wegener theorize continental drift?
#1 Shape of the continents
#2 Fossil clues:
Wegener found similar fossils on different continents
The fossils that he found could probably not have spread between continents
Freshwater reptile fossil
Plant fossil
Similarly evolved species
Why are these two significant? Would finding a bird on two continents support continental drift as well?

8. #3 Climate clues
Wegener found warm climate fossils in the Arctic and cold climate fossils near the equator.
Warm weather fossils
Evidence of glaciers

10. #4 Rock clues
Wegener found similar strata (layers) of rocks on different continents.
Could this be a coincidence?

11. Matching Rock Layers

12. Pangaea – (“all land”) existed about 250 million years ago and began separating around 200 million years ago.
Problem - Wegener’s theory proposed only that the continents were once one supercontinent and they had “moved” apart but could not explain HOW.

13. Things Wegener didn’t know:
What the inside of the Earth looked like
That the Earth was broken into plates
That the location of earthquakes and volcanoes shows plate boundaries
Convection Currents
Was his theory accepted by other scientists?
His theory did not become accepted until the 1950’s/1960’s. Why?
Wegener was appreciated posthumously

15. 1960’s: Harry Hess given credit for providing some of the proof necessary to support Wegener’s theory
Hess’s theory of seafloor spreading
Believed that material moved up at mid-ocean ridges and pushed material outward

18. Mid-Ocean Ridges Discovered in 1950’s

19. Why Did Hess believe that the seafloor was spreading?
The discovery of the mid-ocean ridges
Core samples of ocean floor showed that the age of rocks INCREASED the farther they were from mid-ocean ridges
Core samples also showed corresponding magnetic reversals on each side of the mid-ocean ridge

20. Rock Ages

21. Magnetic Reversals

22. So where are we at this point?
We believe the continents have moved.
These findings provided proof for Hess’s theory and further supported Wegener’s theory
Theory of Plate Tectonics has still not been developed.
But no one still understands why or how the plates move. We are still lacking the MECHANISM.

23. 1960’s Wilson and other scientists gave mechanism to explain HOW the plates are moved.
Scientists proposed that the Earth’s lithosphere is broken into plates, and that CONVECTION CURRENTS in the plastic asthenosphere moved the lithospheric plates above.
All of this information, plus LOTS more, developed into our current theory of Plate Tectonics. 3

24. Mapping Volcanoes

25. Mapping Earthquakes

26. Plate boundaries: This is where two or more lithospheric plates meet
Called faults or boundaries
Lots of tectonic activity (i.e. volcanoes and earthquakes) occurs at these places
Three types:

28. Convergent Boundaries
Two plates colliding (moving together)
If the plates are ocean-continental: Subduction zones, mountains, volcanoes and ocean trenches will form
Oceanic crust is destroyed here
More dense (basalt vs. granite)
Examples are Ring of Fire and Andes Mts
If the plates are both continental
No subduction, only mountain building
Himalayas are example
Crust is neither created nor destroyed

29. “Ring of Fire”

30. Andes Mountains

32. Himalayan Mountains

33. Divergent Boundaries Two plates moving apart
If the plate is an ocean plate:
Forms mid-ocean ridge
Mid-Atlantic Ridge is example
If the plate is continental:
Forms rift valleys
Great Rift Valley is example
New rock is created here

34. Mid-Atlantic Ridge

35. Great Rift Valley

37. Transform Boundaries a.k.a. Strike-Slip boundaries
Two plates sliding/scraping past each other
Earthquakes are common
Crust is neither created nor destroyed
San Andreas Fault and Haiti our examples

39. San Andreas Fault does NOT involve the Juan de Fuca plate

40. Haiti 2010

42. Where would each form?
Volcano
Seafloor Spreading
Mountains
Subduction Zone
Rift Valley
Name two places where each type of boundary would form using your text.

44. Plate Tectonics – late 1960’s Post Harry Hess’ Seafloor Spreading
Plate tectonics (from the Latin tectonicus, from "pertaining to building”) is a scientific theory that describes the large-scale motion of Earth's lithosphere on a molten asthenosphere, due to convection currents caused by the transfer of heat from the Earth’s core.
Plate motions range up to a typical 10–40 mm/year (Mid-Atlantic Ridge; about as fast as fingernails grow), to about 160 mm/year (Nazca Plate; about as fast as hair grows).

45. Why do the plates move?
Solid lithospheric plates move because the plastic asthenosphere is moving.
Radioactive reactions in the core heat magma deep in the Earth which becomes less dense and rises.
As magma cools it becomes more dense, sinks, then reheats, forming CONVECTION CURRENTS (50 million years, though deeper convection can be closer to 200 million years).

46. Measuring plate movement
Scientists NOW use lasers, GPS and satellites to measure plate movement over time.

47. How far would you have to drill through the lithosphere to get to the asthenosphere? 7 – 70 km (4 – 45 miles)