1. Drifting Continents
In a an average lifetime it does not look like the surface of Earth is changing, with the exception of earthquakes, volcanic eruptions, and landslides.
On the geologic time scale Earth is always changing
South America is moving away from Africa at a rate of 2 to 3 cm/y and Hawaii is moving to the northwest at 8 to 9 cm/y

2. Early Scientists Observations
1). Abraham Ortelius
2). Edward Suess
Scientist in the late 1500’s
Noticed the continents on either side of the Atlantic appeared to fit together almost like puzzle pieces
He incorrectly proposed that North and South America had been separated by earthquakes and floods.
Scientist in the late 1800s
Thought that the southern continents had once been joined and called it Gondwanaland

3. Early Scientists Observations
3). Alfred Wegener
 In 1912 he came up with a hypothesis known as continental drift.
Continental Drift = all Earth’s continents were once a single landmass called Pangaea.
Wegner proposed that Pangaea began to break up 200 million years ago and the process is still occurring.
Wegner collected evidence to support his ideas from:
1). Rocks
2). Fossils
3). Climatic Data

4. 2). Evidence from Fossils
Wegner’s Evidence
1). Evidence from Rocks
2). Evidence from Fossils
When Pangaea began to break up, large geologic structures, such as mountain ranges, would have fractured
To prove this he needed to find areas of similar rock types on opposite sides of the Atlantic
He found that rock types in the Appalachians in N. America matched rock types in Greenland and Europe.
Similar fossils and plants have been found on widely separated continents

5. Wegner’s Evidence 3). Ancient Climatic Evidence
Climate Evidence Continued
Coal deposits have been found in Antarctica
Coal forms from dead swamp plants and swamps only occur in an area that is wet and spongy
This indicates that Antarctica was once a warmer and wetter place and must have been located closer to the equator at one time
Glacial deposits in Africa, India, South America, and Australia suggest that there were thick glaciers in these areas.
These areas had to be closer to the South Pole at one time.

6. Problems With Wegner’s Theory
In the early 19oo’s, many scientists still believed that the location of oceans and landmasses were permanent.
Scientists thought Wegener’s hypothesis had 2 major flaws:
1). Wegener had not thoroughly explained what was causing the continents to move.
2). Wegner did not explain how continents could move without shattering.
Wegener died in 1930 without scientists accepting his theory of Continental Drift.
Support did not come until the 1960’s when new evidence was discovered to explain how continents moved.

7. Seafloor Spreading:
Harry Hess was the first scientist to come up with the idea called seafloor spreading
Seafloor Spreading = new ocean crust is formed at ocean ridges and destroyed at deep-sea trenches
Ocean Ridges form because magma is hot and lees dense then surrounding material and is forced upward to fill gaps.
When this magma hardens it turns into new ocean floor
This explains how the continents were drifting apart
Missing Piece of the Puzzle for Wegner

8. Plate Tectonics Plate Boundaries = Where tectonic plates interact
Theory of Plate Tectonics = Earth’s crust and rigid upper mantle are broken into enormous slabs called plates.
These plates move in different directions and different rates
Plate Boundaries = Where tectonic plates interact
3 Main Types of Plate Boundary Interactions:
1). Converge = Plates can come together/moving towards each other
2). Diverge = Plates can move away from one another.
3). Transform = Plates moving by one another/horizontally

9. Types of Plate Boundaries
Convergent
Types of Convergent Boundaries
1). Convergent Boundaries = places where tectonic plates are moving towards one another
1). Oceanic-Oceanic: When 2 pieces of oceanic crust collide
Subduction: 1 of the 2 plates is descending beneath the other.
This creates a deep-sea trench
2). Oceanic –Continental: oceanic crust collides with continental crust
Subduction Occurs
Produces a Trench and Volcanoes
3). Continental-Continental: When 2 pieces of continental crust collide
Forms mountain ranges

10. Types of Plate Boundaries
Divergent
2). Divergent Boundaries = places where plates are moving apart.
Most of these boundaries are found on ocean floors where they form ocean ridges.
This is the area where oceans floors begins to spread
Scientists have measured the rate of growth of the Atlantic Ocean to be 2-3 cm/y
Rift Valleys = when divergent boundaries occur on land.
East Africa

11. Types of Plate Boundaries
Transform
3). Transform Boundaries = places where 2 plates slide horizontally past each other.
These rarely occur on continents
Best example of them occurring on continents is the San Andreas Fault.

12. Magma Composition
Many factors determine the type of magma found beneath volcanoes.
One of the most important factors is viscosity
Viscosity = the internal resistance to flow (how “sticky” a substance is).
Example: Molasses or Cold Maple Syrup have high viscosities.
The viscosity of magma and lave depend upon both temperature and composition
The hotter the magma, the lower the viscosity
The amount of silica increases the viscosity

13. Magma Composition Types of Magma
Magma Composition
Types of Magma
3 Main Types
1). Andesitic
2). Basaltic
3). Rhyolitic
Groups are arranged based upon the viscosity of magma

14. Types of Magma
1). Andesitic
2). Basaltic
Forms from crust being sub-ducted, pushed down, into the Earth’s mantle.
Has an intermediate viscosity.
Mount St. Helens is an example of this magma type.
Forms from rock in the upper mantle melting
Has a Low Viscosity
Flows Easier
Hawaii and Iceland are examples of this magma type.

15. Types of Magma
3). Rhyolitic
Forms from molten material rising and mixing with the crust above it.
High Viscosity
More Resistance
Does not flow with ease

16. Steps to Volcano Formation
Volcanoes
Steps to Volcano Formation
1). Lava or ash and dust erupts through an opening called a vent…
2). As the lava or ash and dust flows onto the surface it cools and hardens around the vent
3). Over time, the hardening lava or ash and dust can accumulate and form a volcano…
4). At the top of the volcano, a bowl shaped depression, called a crater, forms.
5). Large craters = Calderas

17. 3 Main Types of Volcanoes
The appearance of a volcano depends on two factors.
1). The type of material that forms the volcano.
2). The type of eruptions that occur.

18. Types of Volcanoes http://www.youtube.com/watch?v=byJp5o49IF4
Shield Volcanoes
Material: Basaltic Lava
Eruption: Non-Explosive
Shape:
This has a mountain with a broad, gently sloping side and a nearly circular base.
Hawaii

19. Cinder-Cone Volcanoes
Types of Volcanoes
Cinder-Cone Volcanoes
Material: Formed from material being ejected high into the air, falling back to Earth, and piling up around the vent.
Eruption: More Explosive then Shield Volcanoes
Shape:
These volcanoes have steep sides and are generally small.

20. Types of Volcanoes Composite Volcanoes
Material: Formed from layers of volcanic fragments alternating with lava.
Eruption: Can be very Explosive
Shape:
these are much larger then Cinder-Cone Volcanoes
Mount St. Helens
Mount Vesuvius

21. How Do Volcanoes Erupt?
Deep within the Earth it is so hot that some rocks slowly melt and become a thick flowing substance called magma.
Because it is lighter than the solid rock around it, magma rises and collects in magma chambers; areas found beneath volcanoes.
We know high temperature = high pressure. So, the magma chamber is a very hot and high pressure environment.
A volcano erupts when pressure on the magma chamber causes the magma to rise and come out together with gas, rocks and ashes.
Eventually some of the magma pushes through vents and fissures in the Earth's surface.
Magma that has erupted is called lava.

22. Other Volcanic Material
Tephra = rock fragments thrown into the air during an eruption.
they are classified by size
Dust < 0.25 mm
Ash < 2.0 mm
Lapilli > 2.0 mm
The Largest can be the size of a car or small building
Pyroclastic Flow = rapidly moving tephra and volcanic ash that moves down the volcano.
Can move at 200 km/h
Temperatures can exceed 700 degrees Celsius

23. Miscellaneous Volcano Info
Where do Volcanoes Occur?
Most form at plate boundaries
80% at convergent, 15% at divergent
Hot Spots = Volcanoes found far away from plate boundaries
Hawaii was formed by this