CHAPTER 17 PLATE TECTONICS

I. Continental Drift A. Theory 1. the continents are continually moving around the Earth 2. Caused by forces deep within the Earth

B. Alfred Wegner 1. German born scientist proposed the theory of continental drift 3. Is known as the “father” of plate tectonics. 4. Stated the continents were once one large super continent called Pangaea

PANGAEA

Answer the following in your notes  1. Who was the first person to introduce the theory of continental drift?  2. What was the name of the large supercontinent that was composed of all of today’s continents?

The Vocab Quiz on these words has been moved to Weds 10/24/07 because of benchmark testing Pangaea magnetometer magnetic reversals isochron seafloor spreading divergent boundary rift valley convergent boundary subduction transform boundary.

C. Wegner’s Evidence for Continental Drift 1. Continental Fit a) continents appear to fit together like puzzle pieces b) Wegner studied South America and Africa

2. Like fossils and minerals a) similar plant fossils were found on the east coast of S. America and the west coast of Africa b) diamonds and other similar minerals are found on east coast of S. America and the west coast of Africa

3. Evidence of past glaciers are found on both continents, indicating that both continents were at a different latitude at one time

II. Spreading Centers A. Mid- Ocean Ridges 1. Areas where the ocean floor is spreading apart 2. Mid-Atlantic Ridge a) World’s longest volcanic mountain range b) almost completely underwater

MID-ATLANTIC RIDGE

B. Magnetic Reversals 1. Igneous rock records the magnetic polarity of the time when it turns solid a) recorded by the iron minerals in the liquid magma b) each mineral acts like a miniature magnet

2. Reversed Polarity a) Magnetic polarity is opposite of the direction it is today b) Your compass would point to the south instead of north c) Has occurred many times in history and is recorded at the Mid-Ocean ridges

MAGNETIC REVERSAL

C. Age of Igneous Rock 1. The ocean floor is made ofbasalt 2. The farther you travel from the ridge the older the basalt a) new igneous basalt is constantly formed at the spreading center 3. Each side of the mid ocean ridge is like a mirror of the other side

D. Heat Flow 1. the highest measure of heat flow will be at the ridge 2. Heat flow decreases as you move away from the ridge 3. You can expect measurements for heat flow to be the same on each side of the ridge at the same distance away from the ridge

Use your books, starting on page 443 and your notes to answer the following  1. What early evidence suggested that Earth’s continents might be moving?  2. How did Wegener use rock and fossil evidence to support his hypothesis?  3. Why was Wegener’s hypothesis rejected by most scientists of the early 1900s? (pg 446)

1.  The fit of the coastlines of the continents.

2.  Similar rocks and fossils were found on continents on opposite sides of the Atlantic Ocean

3.  Wegner could not explain what was moving the continents and how the continents were moving.

III.. Plate Tectonics A. Modern Theory 1. The Earth is broken up into several sections called plates 2. explains how the plates move a) lithosphere moves over the asthenosphere

B. Types of Plate Boundaries 1. Divergent plate boundary a) area where two plates are moving away from each other b) tension is pulling the plates apart c) forms a normal fault

DIVERGENT PLATE BOUNDARY

2.Convergent boundaries a) area where two plates are running into each other -There are three types of convergent boundaries.

b) Ocean-continent converging: the ocean plate always goes under the continent. Ocean plates are more dense. The end of the ocean plate melts and the rising magma forms volcanoes.

OCEAN-CONTINENT CONVERGING SUBDUCTION ZONE

c) Ocean-ocean converging- the denser ocean plate goes underneath the less dense ocean plate. The plate underneath melts and the rising magma forms island arcs ( Ex. Japan)

OCEAN-OCEAN CONVERGING SUBDUCTION ZONE

d) continent-continent converging- two continent plates crash into each other. Neither plate will go underneath the other. Both plate ends crumple and form mountains ( Ex, Himalayans, form as India is crashing into Asia)

CONTINENT-CONTINENT CONVERGING COLLISION ZONE

3.Transform (Sliding) Plate Boundaries a) One plate is sliding past another b) forms a transform fault c) Ex. San Andreas Fault

TRANSFORM BOUNDARY

III. Other Plate Tectonic Facts A. How do plates move? 1. Movement is caused by huge convection currents inside the Earth

CONVECTION CURRENTS

B. Isostacy 1. The Crust is rising a) rock material is eroded off the top of the crust b) this decrease in weight allows the crust to rise

C. Crustal Thickness 1. Continental crust is thicker a) is much less dense than ocean crust b) will float on ocean crust c) is mostly granite 2. Oceanic crust a) is almost completely basalt b) very dense c) always sinks underneath continental crust

D. Hot Spot 1. An area in the middle of the crust with a high heat flow a) magma is rising upward through the crust 2. Causes volcanoes and volcanic islands to form a) Ex. Hawaii 3. The hot spot never moves a) the plate moves over the hot spot causing old volcanoes to become extinct and new volcanoes to form.

Use your notes to answer the following  1. Compare and contrast normal magnetic polarity and reversed magnetic polarity.  2. Where in the USA is there a prominent transform boundary?  3. Why do you think earthquakes are common along plate boundaries? (What is happening at these boundaries?)  3. Why do you think earthquakes are common along plate boundaries? (What is happening at these boundaries?)

Use your notes to answer the following  1. What type of crust is the thickest?  2. What type of crust is the most dense?  3. Give an example of islands that form over a hot spot.  4. According to the idea of isostacy, what causes the crust to rise?