1. Developing an Understanding of Plate Tectonics

2. The Inner Earth Layered Hot
Beneath its familiar surface & thin crust lie a rocky mantle & iron core
Hot
Core = hotter than surface of the Sun
Escape of inner heat to cold outer space causes plates to move

3. The Inner Earth Flows & Churns
Flowing rocks in the mantle help move plates above
In outer core, churning dynamo of liquid iron generates Earth’s magnetic field

4. The Inner Earth First 100 million years…
Ever-larger particles in new Solar System collided & stuck together creating lots of heat
Earth gradually increased in size, melted completely & layers began to form

5. The Inner Earth Layers Forming Dense molten iron sank & created core
Lighter silicate liquid rose & cooled, forming the mantle
Later, partial melting of mantle produced the crust
Process continues today!

6. Animations Crust (very thin-3-30 miles thin; 5-50km, up to 70km)
Mantle (mobile)
Core (HOT!)
A knowledge of earth's interior is essential for understanding plate tectonics. A good analogy for teaching about earth's interior is a piece of fruit with a large pit such as a peach or a plum. Most students are familiar with these fruits and have seen them cut in half. In addition the size of the features are very similar.
If we cut a piece of fruit in half we will see that it is composed of three parts: 1) a very thin skin, 2) a seed of significant size located in the center, and 3) most of the mass of the fruit being contained within the flesh. Cutting the earth we would see: 1) a very thin crust on the outside, 2) a core of significant size in the center, and 3) most of the mass of the Earth contained in the mantle.
Animations

7. Animation Oceanic Crust *3-4 miles thin (5-7km) *Basalt
Continental Crust *20-43 miles thin (30-70 km) *Granite
There are two different types of crust: thin oceanic crust that underlies the ocean basins and thicker continental crust that underlies the continents. These two different types of crust are made up of different types of rock. The thin oceanic crust is composed of primarily of basalt and the thicker continental crust is composed primarily of granite. The low density of the thick continental crust allows it to "float" in high relief on the much higher density mantle below.
Granite vs. Basalt
Animation

8. The Crust—Earth’s Thin Skin

9. Basalt vs. Granite Rock Basalt Both Granite
Extrusive—magma breaks through the crust of the earth and erupts on the surface (volcanic eruptions)
“Blood of the earth”
Makes new seafloor crust
Because the magma comes out of earth (and usually into water) it cools very quickly, and minerals have little opportunity to grow
Fine grained—individual mineral grains are nearly impossible to see without magnification
Generally dark in color, thin, & heavy
High density due to amount of iron, magnesium and other heavy elements
Igneous rock (cooled from magma)
Large amounts of silicon & oxygen
Most common rock on continental land masses
Ex: Yosemite Valley & Mt. Rushmore
Intrusive—magma was trapped deep in the crust & took a long time to cool and crystallize into solid rock
Coarse-textured rock—individual mineral grains are easily visible
Light compared to basalt
Accumulates into continent-sized rafts which bob in “sea of basalt”
Granite is the ultimate silicate rock. As discussed elsewhere in greater detail, on average oxygen and silicon account for 75% of the earth's crust. The remaining 25% is split among several other elements, with aluminum and potassium contributing the most to the formation of the continental granitic rocks. Relatively small amounts of iron and magnesium occur, but since they have generally higher densities it's not surprising that there isn't very much in the granite. Due to the process of differentiation, most of the heavier elements are moving towards the core of the earth, allowing the silicon and oxygen to accumulate on the surface. And accumulate it has. Enough granitic "scum" has differentiated to the surface to cover 25% to 30% of the earth with the good stuff. We call this purified material felsic because of the relatively high percentage of silica and oxygen.

10. The Mantle—Deep & Dense
~84% of Earth’s volume
Uppermost 100 km is rigid
Makes up Lithosphere with crust (plates)

11. The Mantle—Deep & Dense
Next layer makes up Asthenosphere (part of Upper Mantle, km below surface)
Solid, hot, and soft
Flows like a glacier
Lower Mantle
Extremely dense

12. The Core—Iron Center Outer Core is molten
Hot enough to be as fluid as water
Motions create Earth’s magnetic field

13. The Core—Iron Center Inner Core is solid metal
Immense pressure  solid state

14. The Unreachable Frontier— Looming Questions
In 1990, the world’s deepest drill hole penetrated to a depth of 12.3 km (7.6 mi) beneath Russia’s Kola Peninsula.
More than 99% to center of Earth lay beneath the drill bit.
If the inner Earth is so remote AND inaccessible, HOW can we possibly learn anything about it??

15. The Scientific Method?
Geologists do not apply the scientific method in a traditional sense.
Many traditional scientific hypotheses are tested by controlled lab experiments that take place over a short period of time (minutes to a few years)
For geology, there are too many variables
Too large
Very SLOW processes
Experimenter must outlive the experiment and geologists cannot reasonably run experiments that precisely duplicate processes that are require centuries or millions of years in nature!
Smith, Gary and Aurora Pun. How Does Earth Work? Upper Saddle River, Pearson Education p. 9

16. The Scientific Method?
Earth is the laboratory for many geoscience research objectives.
Geologists assess critical questions through careful observation.
Observing or measuring features in rocks or landscapes that the hypothesis predicts should be present
Analytical laboratories measure chemical element abundance in rocks including density and magnetic characteristics
Other experiments simulate elevated temperature and pressure within Earth’s interior
Computer simulations can “speed up” time to reproduce Earth processes and variables can be changed one at a time to examine their effects on outcomes.
Constrained by necessary assumptions or simplifications
Smith, Gary and Aurora Pun. How Does Earth Work? Upper Saddle River, Pearson Education p. 9

17. How Do We Know About the Core—The Unreachable Frontier?
Geologist gather clues from
Meteorites
Rocks
Diamonds
Earthquake waves
Earth’s magnetic field

18. A flash of light in the midnight sky announces the arrival of another messenger from space: a meteorite. These extraterrestrial rocks testify to the origin of the Solar System and of the inner Earth. Asteroids — the parent bodies of most meteorites — originated at the same time as the Sun, Earth, and other planets. When fragments of asteroids land here as meteorites, we glimpse the raw materials that formed our planet and the secrets of its core.

19. Clues from Rocks
Learn about the inner Earth from special rocks called peridotites—from the upper mantle.
Peridotites record geological processes that take place in this inaccessible layer of Earth.
It's no coincidence that most peridotites are olive green. Some of their color comes from olivine, the most abundant mineral in Earth's upper mantle

20. Chondrites—meteorites composed of Solar System’s original dust
7 elements make up 97% of crust
But, compared to chondrites, Earth’s crust & mantle are poor in iron
Deduce that iron must be concentrated in core.

21. Meteorites from same Asteroid (parent material)
Earth’s rocky mantle & iron core may be separated by a similar hybrid zone.
Iron meteorite came from asteroid’s core (large crystals of metal)
These two meteorites probably came from the core and mantle of the same asteroid. The pallasite came from the asteroid's core-mantle boundary, where olivine from the mantle mixed with iron-nickel metal from the core. Earth's rocky mantle and iron core may be separated by a similar hybrid zone. The iron meteorite came from the asteroid's core. Notice the large crystals of metal. Some scientists have proposed that Earth's core is a single crystal of iron!

22. When magma rises rapidly to the surface, dense chunks of upper mantle can “hitch a ride”.
Called xenoliths or “stranger rocks”

23. Clues from Diamonds

24. Clues from Diamonds Require tremendous temperature & pressure
Hardest material known
Occur at depths greater than 150km
Come to surface with rapidly rising magma
Kimberlite & lamproite (partial melting of upper mantle)

25. Clues from Earthquakes
Earthquakes release energy that
races through planet as seismic waves.
Material type changes speed of waves
Arrival times of different waves around world provide clues to composition of inner Earth
At the boundaries between Earth's layers, seismic waves are refracted and reflected. The two kinds of interior seismic waves behave in different ways:
P-waves (primary or pressure waves) travel through liquids and solids.
S-waves (secondary or shear waves) travel through solids only.
Strong ground motion associated with the 1964 Alaska earthquake caused the sliding that destroyed these homes.

26. Clues from Earth’s Magnetic Field
Like a bar magnet, Earth has a magnetic field with 2 main poles
Generated by motions within the outer core
Dynamic electromagnet
Planet’s rotation causes molten iron-nickel in outer core to circulate
Creates electrical currents & magnetic field
Are Earth’s Magnetic Poles Stable?
No. They wander over the Earth’s surface. Since 1945, they have moved at a rate of almost 12 km a year — a clue to the dynamic origin of our magnetic field. About every 500,000 years Earth's magnetic field gets progressively weaker, vanishes, then reappears with the magnetic North and South poles reversed.
If you're standing at the North Pole, you're about 15 degrees (1,670 km, or 1,035 mi) away from its slowly migrating magnetic pole.

27. Principles, Laws, & Theories
Principles (or laws) are generalizations about how nature is observed to work
Example: Seventeenth century astronomer Johannes Kepler stated the first law of planetary motion, which states that planets orbit the Sun along an elliptical orbit
Law derives from many undisputed observations but does not offer an explanation for why planets follow elliptical paths around the Sun.
Smith, Gary and Aurora Pun. How Does Earth Work? Upper Saddle River, Pearson Education p. 10

28. Principles, Laws, & Theories
Theories offer well-tested and accepted explanations, not offhand hunches, or why the natural system works this way.
Example: The theory describing gravity forces between objects offers an explanation for Kepler’s First Law of Planetary Motion
Smith, Gary and Aurora Pun. How Does Earth Work? Upper Saddle River, Pearson Education p. 10

29. Principle of Uniformitarianism
Geologic processes and natural laws now operating on and within Earth have acted throughout geologic time; the logic and method by which geologists reconstruct past events.
James Hutton & Charles Lyell published Principles of Geology in 3 volumes
Smith, Gary and Aurora Pun. How Does Earth Work? Upper Saddle River, Pearson Education p. 10

30. Applying Uniformitarianism
Modern Beach & Ancient Rock
Similarities of modern & ancient features indicate that the ancient rock formed in an environment similar to a beach
Geologists interpret features preserved in ancient rocks in terms of observed processes
Smith, Gary and Aurora Pun. How Does Earth Work? Upper Saddle River, Pearson Education p. 11

31. Modern View of Uniformitarianism
Should rate of processes be uniform through time and limited to the values measured during the history of geologic study?
Is it possible for processes to have been active in the past that humans have not witnessed or for such processes to have operated at different rates?
Smith, Gary and Aurora Pun. How Does Earth Work? Upper Saddle River, Pearson Education p. 12

32. Modern View of Uniformitarianism
Many geologic processes occur episodically (e.g. collisions of meteors and comets with Earth)
Or, over a wide range of scale (e.g., volcanic eruptions, floods)
Geologic observations have only been made over 2 centuries for 5 millennia of recorded history
If primordial Earth was hotter, could processes driven by thermal energy have taken place at faster rates?
Would not rates of erosion have been higher before the appearance of rooted plants on land beginning 400 mya?
Cannot place too many restrictions on applying uniformitarianism, especially with regard to the rates & conditions of processes that might change over time.
Smith, Gary and Aurora Pun. How Does Earth Work? Upper Saddle River, Pearson Education p. 12

33. 1964 Earthquake—Alaska
Smith, Gary and Aurora Pun. How Does Earth Work? Upper Saddle River, Pearson Education p. 12
Uplift during an earthquake in Alaska in 1964 raised ground in several areas. Adding up the uplift during many earthquakes over long intervals of geologic time explains the elevations of mountains.

34. Pangaea Video Discussion Questions:
Is Earth's surface stable and stationary now? Was it ever in the past? Do you think it will be stable in the future?
Do you think that the way continents fit together is convincing evidence for the theory of plate tectonics? Why or why not?
What was the supercontinent called that once contained nearly all of the continental crust? Research what the name means.
Which ocean is growing in size? Which is shrinking? Explain why this is occurring.
How does the theory of plate tectonics help us explain natural phenomena such as earthquakes and mountains, which geologists had difficulty accounting for prior to the development of the theory?

35. Theory of Plate Tectonics
Theory that Earth’s outer shell (lithosphere) is not seamlessly continuous but is broken into discrete pieces that move slowly relative to one another and change in size over geologic time.
Most important geologic theory
From 1960s

36. Plate
One of several discrete, rigid to semi-rigid, roughly 100-km-thick slabs that make up Earth’s lithosphere
7 Major Plates
Pacific
North American
South American
African
Eurasian
Indian-Australian
Antarctic

37. Plate Boundaries
Motion between adjacent plates describes the type of boundary between plates

38. Types of Plate Boundaries
Tectonics—study of the causes of rock deformation
3 Basic types of conceivable relative motions between two plates at mutual boundaries
Divergent plate boundaries
Convergent plate boundaries
Transform plate boundaries

39. Divergent Plate Boundaries
Linear or curving zones where plates move apart from one another and new lithosphere forms

40. Animation http://geology.com//nsta/divergent-plate-boundaries.shtml
When a divergent boundary occurs beneath oceanic lithosphere, the rising convection current below lifts the lithosphere producing a mid-ocean ridge. Extensional forces stretch the lithosphere and produce a deep fissure. When the fissure opens, pressure is reduced on the super-heated mantle material below. It responds by melting and the new magma flows into the fissure. The magma then solidifies and the process repeats itself.  The Mid-Atlantic Ridge is a classic example of this type of plate boundary. The Ridge is a high area compared to the surrounding seafloor because of the lift from the convection current below. (A frequent misconception is that the Ridge is a build-up of volcanic materials, however, the magma that fills the fissure does not flood extensively over the ocean floor and stack up to form a topographic high. Instead, it fills the fissure and solidifies. When the next eruption occurs, the fissure most likely develops down the center of the cooling magma plug with half of the newly solidified material being attached to the end of each plate. 
Visit the Interactive Plate Boundary Map to explore satellite images of divergent boundaries between oceanic plates. Two locations are marked: 1) the Mid-Atlantic Ridge exposed above sea level on the island of Iceland, and 2) the Mid-Atlantic Ridge between North America and Africa.  Effects that are found at a divergent boundary between oceanic plates include: a submarine mountain range such as the Mid-Atlantic Ridge; volcanic activity in the form of fissure eruptions; shallow earthquake activity; creation of new seafloor and a widening ocean basin.
Animation

41. Animation http://geology.com//nsta/divergent-plate-boundaries.shtml
When a divergent boundary occurs beneath a thick continental plate, the pull-apart is not vigorous enough to create a clean, single break through the thick plate material. Here the thick continental plate is arched upwards from the convection current's lift, pulled thin by extensional forces,and fractured into a rift-shaped structure. As the two plates pull apart, normal faults develop on both sides of the rift and the central blocks slide downwards. Earthquakes occur as a result of this fracturing and movement. Early in the rift-forming process, streams and rivers will flow into the sinking rift valley to form a long linear lake. As the rift grows deeper it might drop below sea level allowing ocean waters to flow in. This will produce a narrow, shallow sea within the rift. This rift can then grow deeper and wider. If rifting continues a new ocean basin could be produced. 
Effects that are found at this type of plate boundary include: a rift valley sometimes occupied by a long linear lakes or a shallow arm of the ocean, numerous normal faults bounding a central rift valley and shallow earthquake activity along the normal faults. Volcanic activity sometimes occurs within the rift. 
Animation

42. East Africa Rift Valley
Interactive Plate Boundary Map
The East Africa Rift Valley is a classic example of this type of plate boundary. The East Africa Rift is in a very early stage of development. The plate has not been completely rifted and the rift valley is still above sea level but occupied by lakes at several locations. The Red Sea is an example of a more completely developed rift. There the plates have fully separated and the central rift valley has dropped below sea level. 

43. Convergent Plate Boundary
Curving zone where plates collide nearly head-on into one another, compressing the lithosphere and causing subduction of one plate beneath the other
Subduction—the process by which a lithospheric plate descends beneath a neighboring plate

44. When continental and oceanic plates collide the thinner and more dense oceanic plate is overridden by the thicker and less dense continental plate. The oceanic plate is forced down into the mantle in a process known as "subduction". As the oceanic plate descends it is forced into higher temperature environments. At a depth of about 100 miles (160 km) materials in the subducting plate begin to approach their melting temperatures and a process of partial melting begins.  This partial melting produces magma chambers above the subducting oceanic plate. These magma chambers are less dense than the surrounding mantle materials and are buoyant. The buoyant magma chambers begin a slow asscent through the overlying materials, melting and fracturing their way upwards. The size and depth of these magma chambers can be determined by mapping the earthquake activity arround them. If a magma chamber rises to the surface without solidifying the magma will break through in the form of a volcanic eruption.  The Washington-Oregon coastline of the United States is an example of this type of convergent plate boundary. Here the Juan de Fuca oceanic plate is subducting beneath the westward moving North American continental plate. The Cascade Mountain Range is a line of volcanoes above the melting oceanic plate. The Andes Mountain Range of western South America is another example of a convergent boundary between an oceanic and continental plate. Here the Nazca Plate is subducting beneath the South American plate.  Visit the Interactive Plate Boundary Map to explore satellite images of convergent boundaries between oceanic and continental plates. Two locations are marked to show this type of plate boundary - the Cascade volcanoes along the Washington-Oregon coast of North America and the Andes mountain range on the western margin of South America.  Effects of a convergent boundary between an oceanic and continental plate include: a zone of earthquake activity that is shallow along the continent margin but deepens beneath the continent, sometimes an ocean trench immediately off shore of the continent, a line of volcanic eruptions a few hundred miles inland from the shoreline, destruction of oceanic lithosphere.
Animation

45. Animation http://geology.com//nsta/convergent-plate-boundaries.shtml
When a convergent boundary occurs between two oceanic plates one of those plates will subduct beneath the other. Normally the older plate will subduct because of its higher density. The subducting plate is heated as it is forced deeper into the mantle and at a depth of about 100 miles (150 km) the plate begins to melt. Magma chambers are produced as a result of this melting and the magma is lower in density than the surrounding rock material. It begins ascending by melting and fracturing its way throught the overlying rock material. Magma chambers that reach the surface break through to form a volcanic eruption cone. In the early stages of this type of boundary the cones will be deep beneath the ocean surface but later grow to be higher than sea level. This produces an island chain. With continued development the islands grow larger, merge and an elongate landmass is created.  Japan, the Aleutian islands and the Eastern Caribbean islands of Martinique, St. Lucia and St. Vincent and the Grenadines are examples of islands formed through this type of plate boundary. Visit the Interactive Plate Boundary Map to explore satellite images of these three areas.  Effects that are found at this type of plate boundary include: a zone of progressively deeper earthquakes, an oceanic trench, a chain of volcanic islands, and the destruction of oceanic lithosphere.
Animation

46. Animation http://geology.com//nsta/convergent-plate-boundaries.shtml
This is a difficult boundary to draw. First it is complex and second, it is poorly understood when compared to the other types of plate boundaries. In this type of convergent boundary a powerful collision occurs. The two thick continental plates collide and both of them have a density that is much lower than the mantle, which prevents subduction (there may be a small amout of subduction or the heavier lithosphere below the continental crust might break free from the crust and subduct).  Fragments of crust or continent margin sediments might be caught in the collision zone between the continents forming a highly deformed melange of rock. The intense compression can also cause extensive folding and faulting of rocks within the two colliding plates. This deformation can extend hundreds of miles into the plate interior.  The Himalaya Mountain Range is the best active example of this type of plate boundary. Visit the Interactive Plate Boundary Map to explore satellite images of the Himalaya Range where the Indian and Eurasian plates are currently in collision. The Appalachian Mountain Range is an ancient example of this collision type and is also marked on the map.  Effects found at a convergent boundary between continental plates include: intense folding and faulting, a broad folded mountain range, shallow earthquake activity, shortening and thickening of the plates within the collision zone. 
Animation

47. Transform Plate Boundary
Zones where lithospheric plates slide past one another with neither creation nor destruction of lithosphere

48. Animation http://geology.com//nsta/transform-plate-boundaries.shtml
Transform faults can be distinguished from the typical strike-slip faults because the sense of movement is in the opposite direction (see illustration at right). A strike-slip fault is a simple offset, however, a transform fault is formed between two different plates, each moving away from the spreading center of a divergent plate boundary. When you look at the transform fault diagram above, imagine the double line as a divergent plate boundary and visualize which way the diverging plates would be moving. A smaller number of transform faults cut continental lithosphere. The most famous example of this is the San Andreas Fault Zone of western North America. The San Andreas connects a divergent boundary in the Gulf of California with the Cascadia subduction zone. Another example of a transform boundary on land is the Alpine Fault of New Zealand. Both the San Andreas Fault and the Alpine Fault are shown on our Interactive Plate Tectonics Map.  Transform faults are locations of recurring earthquake activity and faulting. The earthquakes are usually shallow because they occur within and between plates that are not involved in subduction. Volcanic activity is normally not present because the typical magma sources of an upwelling convection current or a melting subducting plate are not present. 
Animation

54. What next?
By understanding Plate Tectonics, we can better understand other geologic processes, such as earthquakes and volcanoes. Studying these processes continues to feed our understanding of Plate Tectonics.
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