1. Plate Tectonics

2. Ag Earth Science – Chapter 9.1
9.1 Vocabulary

3. continental drift
A hypothesis that originally proposed that the continents had once been joined to form a single supercontinent

4. Pangaea
The proposed supercontinent that 200 million years ago began to break apart and form the present landmasses

5. An Idea Before Its Time
German scientist names Alfred Wegener proposed the hypothesis of continental drift.
Continental Drift – the continents had once been joined to form a single supercontinent
Pangaea – The name of the “supercontinent” meaning all land.

6. Evidence for Continental Drift Hypothesis
The continental puzzle – continents fit together like a puzzle
Matching fossils – fossil evidence for continental drift includes several fossil organisms found on different continents.
Rock type and structures – rock evidence for continental drift exists in the form of several mountain belts that end at one coastline, only to reappear on a landmass across the ocean.
Ancient climates – ancient climate evidence supported continental drift

7. A New Theory Emerges
During the years that followed Wegener’s hypothesis, major strides in technology enabled scientists to map the ocean floor.
Extensive data on earthquakes and the Earth’s magnetic field led to a new theory known as plate tectonics.

8. Ag Earth Science – Chapter 9.2
9.2 Vocabulary

9. plate tectonics
The theory that proposes that the earth’s outer shell consists of individual plates that interact in various ways and thereby produce earthquakes, volcanoes, mountains and the crust itself

10. plate
One of numerous rigid sections of the lithosphere that moves as a unit over the material of the asthenosphere

11. divergent boundary
A region where the rigid plates are moving apart, typified by the oceanic ridges.

12. convergent boundary
A boundary in which two plates move together

13. transform fault boundary
A boundary in which two plates slide past each other without creating or destroying lithosphere

14. Earth’s Major Plates
According to the plate tectonic theory, the uppermost mantle, along with the overlying crust, behaves as a strong, rigid layer. This layer is known as the lithosphere.
The lithosphere is divided into plates.

15. Types of Plate Boundaries
The three main types of boundaries are convergent, divergent, and transform fault boundaries.
Divergent Boundaries – two plates move APART

16. Types of Plate Boundaries
The three main types of boundaries are convergent, divergent, and transform fault boundaries.
Convergent Boundaries – two plates move TOGETHER

17. Types of Plate Boundaries
The three main types of boundaries are convergent, divergent, and transform fault boundaries.
Transform Fault Boundaries – two plates grind past each other side-by-side

18. Ag Earth Science – Chapter 9.3
9.3 Vocabulary

19. oceanic ridge
A continuous elevated zone on the floor of all major ocean basins and varying in width from 600 miles to 2400 miles. The crests of ridges represent divergent plate boundaries.

20. rift valley
Deep faulted structure found along the axes of divergent plate boundaries. Can be found on seafloor or land.

21. seafloor spreading
The process by which plate tectonics produces new oceanic lithosphere at ocean ridges

22. subduction zone
A destructive plate margin where oceanic crust is being pushed down into the mantle beneath a second plate

23. trench
A surface feature in the seafloor produced by the descending plate during subduction

24. continental volcanic arc
Mountains formed in part by volcanic activity caused by the subduction of oceanic lithosphere beneath a continent

25. volcanic island arc
A chain of volcanic islands generally located a few hundred miles from a trench where subduction of one oceanic slab beneath another is occurring

26. Divergent Boundaries
Most divergent boundaries are located along the crests of oceanic ridges.
Along well-developed divergent plate boundaries, the seafloor is elevated, forming the oceanic ridge.
Deep faulted structures called rift valleys are found along the axes of some segments.

27. Divergent Boundaries
Seafloor spreading is the process by which plate tectonics produces new oceanic lithosphere.

28. Divergent Boundaries
Continental Rifts - When spreading centers develop within a continent, the landmass may split into two or more smaller segments.

29. Convergent Boundaries
As two plates slowly converge (come together head on), the leading edge of one plate is bent downward, allowing it to slide beneath the other.
Destructive plate margins where oceanic crust is being pushed down into the mantle are called SUBDUCTION ZONES.
A subduction zone occurs when one oceanic plate is forced down into the mantle beneath a second plate.

30. Convergent Boundaries
Oceanic – Continental
When the leading edge of a continental plate converges with an oceanic plate, the less dense continental plate remains floating.
Continental volcanic arc / volcanic activity is caused by the subduction of the oceanic crust melting below when it sinks into the asthenosphere.

31. Convergent Boundaries
Oceanic – Oceanic
When two oceanic slabs converge, one descends beneath the other. 
This causes similar volcanic activity to what occurs with oceanic-continental boundary, however the volcanoes form on the ocean floor.
The newly formed land consisting of an arc shaped chain of small volcanic islands is called a volcanic island arc. (example – Aleutian Islands near Alaska)

32. Convergent Boundaries
Continental – Continental
When an oceanic plate is subducted beneath continental lithosphere, a continental volcanic arc is created. However, if the subducting plate also has continental lithosphere, the subduction eventually brings the two continents together and the collision forms complex mountains.

33. Transform Boundaries
At a transform fault boundary, plates grind past each other without destroying the lithosphere.
Example – San Andreas Fault