1. Continental Drift and Plate Tectonics
Birth of a Theory
Continental Drift and Plate Tectonics

2. Wegener’s Hypothesis
Alfred Wegener proposed that all the continents were once joined together in a single super continent called Pangaea.
He proposed that it began to break apart around 200 million years ago.
This is the continental drift hypothesis

4. Evidence for his theory
Continental Puzzle
Fossil evidence of several organisms of the same species on different landmasses.( Glossopteris Fern, Mesosaurus Reptile)
Rock types and structures
And climate evidence.

6. Problems with his theory
Couldn’t provide a mechanism for how the continents moved.

7. A new Theory
Plate Tectonic theory- says the earth is made up of rigid plates that contain the crust and upper mantle also known as the lithosphere moving long the asthenosphere.
Lithosphere- the crust and upper mantle
Asthenosphere- Plastic like layer of mantle beneath the crust

8. Plate Boundaries
Divergent boundaries (also called spreading centers) are the place where two plates move apart.
Convergent boundaries form where two plates move together.
Transform fault boundaries are margins where two plates grind past each other without the production or destruction of the lithosphere.

10. Evidence for Plate Tectonics
Mid-Ocean ridges and rift valleys that cause sea floor spreading provided a mechanism for the plate tectonic theory.
Seafloor spreading process that produces new oceanic lithosphere.
subduction zone occurs when one oceanic plate is forced down into the mantle beneath a second plate.

13. Convergent Plate Boundaries
Oceanic-Continental-
Continental volcanic arcs form in part by volcanic activity caused by the subduction of oceanic lithosphere beneath a continent.
Examples include the Andes, Cascades, and the Sierra Nevadas

18. Types of Stress
The three types of stresses that rocks commonly undergo are tensional stress, compressional stress, and shear stress

20. Faults
Normal faults occur when the hanging wall block moves down relative to the footwall block.
Reverse faults are faults in which the hanging wall block moves up relative to the footwall block.
Reverse Thrust faults are reverse faults in which hanging wall moves up and over the footwall.
Strike-slip faults are faults in which the movement is horizontal and parallel to the trend, or strike, of the fault surface.

22. Earthquakes
earthquake is the vibration of Earth produced by the rapid release of energy
Focus is the point within Earth where the earthquake starts.
Epicenter is the location on the surface directly above the focus
Faults are fractures in Earth where movement has occurred

25. Cause of Earthquakes
Most earthquakes are produced by the rapid release of elastic energy stored in rock that has been subjected to great forces.
When the strength of the rock is exceeded, it suddenly breaks, causing the vibrations of an earthquake.

27. Earthquakes cont.
An aftershock is a small earthquake that follows the main earthquake.
A foreshock is a small earthquake that often precedes a major earthquake

28. Earthquake Waves
Seismographs are instruments that record earthquake waves.
Seismograms are traces of amplified, electronically recorded ground motion made by seismographs
Surface waves are seismic waves that travel along Earth’s outer layer.

31. Earthquake Waves cont.
P waves- push-pull waves that push (compress) and pull (expand) in the direction that the waves travel.
Travel through solids, liquids, and gases
Travel the fastest

32. Earthquake Waves Cont.
S waves-Seismic waves that travel along Earth’s outer layer.
Shake particles at right angles to the direction that they travel.
Travel only through solids
Slower velocity than P waves

35. Richter Scale Based on the amplitude of the largest seismic wave
Each unit of Richter magnitude equates to roughly a 32-fold energy increase
Does not estimate adequately the size of very large earthquakes

36. Momentum Magnitude
Derived from the amount of displacement that occurs along the fault zone
Moment magnitude is the most widely used measurement for earthquakes because it is the only magnitude scale that estimates the energy released by earthquakes
Measures very large earthquakes

39. Volcanoes Factors that determine the violence of an eruption
Composition of the magma
Temperature of the magma
Dissolved gases in the magma
Viscosity is the measure of a material's resistance to flow.

40. Factors affecting Eruptions
Temperature (hotter magmas are less viscous)
Composition (silica content
Gases
A vent is an opening in the surface of Earth through which molten rock and gases are released.

44. Volcanic Materials
Pyroclastic materials is the name given to particles produced in volcanic eruptions.
Types of pyroclastic material
Ash and Dust- very fine in sized
Cinders- Pea Sized
Bombs- large sized

45. Types of Volcanoes
Shield volcanoes are broad, gently sloping volcanoes built from fluid basaltic lavas
Cinder cones are small volcanoes built primarily of pyroclastic material ejected from a single vent.
Composite cones are volcanoes composed of both lava flows and pyroclastic material
Most violent type of activity