PLATE BOUNDARIES PLATE TECTONICS CONTINENTAL DRIFT PANGAEA CHAPTER 7 CHAPTER 7 Sections 1-3

Why do lithospheric plates move? 1. Convection Currents: A current of heat flows from the core to the crust. This movement of magma causes plates to move. -Ridge push -Slab pull

Tectonic Plate Theory The theory of plate tectonics was developed in the 1960's. This theory explains the movement of the Earth's plates (which has since been documented scientifically) and also explains the cause of earthquakes, volcanoes, oceanic trenches, mountain range formation, and many other geologic phenomenon. The plates are moving at a speed that has been estimated at 1 to 10 cm per year. Most of the Earth's seismic activity (volcanoes and earthquakes) occurs at the plate boundaries.

What happens at these plate boundaries? Sea-Floor Spreading- new ocean floor created Volcanoes Earthquakes Mountain building

TYPES OF PLATE MOVEMENT: Divergent, Convergent and Transform Boundaries Divergent Boundary- Plates move away from each other Convergent Boundary-Plates move toward each other Transform Boundary- Plates move past each other

Plate Boundaries and Movement

Divergent Boundary Plates move away from each other. Seafloor spreading is the movement of two oceanic plates away from each other, which results in the formation of new oceanic crust along the Mid - Atlantic Ridge.

On-land exposure of the Mid-Atlantic Ridge in Iceland. Divergent Boundary

Iceland and the Mid-Atlantic Ridge

Mid-Atlantic Ridge or Mid-Ocean Ridge (Divergent Boundary- Sea floor spreading)

Convergent Boundary When two plates collide (at a convergent plate boundary), some crust is destroyed in the impact and the plates become smaller. The results differ, depending upon what types of plates are involved. 1.Oceanic Plate and Continental Plate - When a thin, dense oceanic plate collides with a relatively light, thick continental plate, the oceanic plate is forced under the continental plate; this phenomenon is called subduction zone. 2. Two Oceanic Plates - When two oceanic plates collide, one may be pushed under the other and magma from the mantle rises, forming volcanoes in the vicinity. 3. Two Continental Plates - When two continental plates collide, mountain ranges are created as the colliding crust is compressed and pushed upwards.

Oceanic Continental SUBDUCTION ZONE

Oceanic Volcanoes will usually form in the area.

Continental Continental Mountains are formed.

Transform Boundary Two tectonic plates move past one another. Their edges are jagged and irregular. As they grind together and jerk, they slide past each other creating earthquakes.

Transform Boundary This is what is happening in California along the San Andreas Fault. Two plates are moving past each other, causing earthquakes.

San Andreas Fault, California

Animation- Plate Boundaries

Alfred Wegener, Pangaea and Continental Drift In 1915, the German geologist and meteorologist Alfred Wegener ( ) first proposed the theory of continental drift, which states that parts of the Earth's crust slowly drift atop a liquid core.Alfred Wegener The fossil record supports and gives credence to the theories of continental drift and plate tectonics. Wegener hypothesized that there was an original, gigantic supercontinent 200 million years ago, which he named Pangaea, meaning "All-earth". Pangaea was a supercontinent consisting of all of Earth's land masses.. Pangaea started to break up into two smaller supercontinents, called Laurasia and Gondwanaland, during the Jurassic period. By the end of the Cretaceous period, the continents were separating into land masses that look like our modern-day continents. Wegener published this theory in his 1915 book, On the Origin of Continents and Oceans. In it he also proposed the existence of the supercontinent Pangaea, and named it (Pangaea means "all the land" in Greek).Pangaea

This process of continental drift took place over MILLION of years

Evidence Supporting Continental Drift The Shapes Match The Plants and Animals Match The Rocks Match

The Shapes Match The continents look as if they were pieces of a giant jigsaw puzzle that could fit together to make one giant super- continent.

The Plants and Animals Match Wegener noted that plant fossils of late Paleozoic age found on several different continents were quite similar. This suggests that they evolved together on a single large land mass. He was intrigued by the occurrences of plant and animal fossils found on the matching coastlines of South America and Africa, which are now widely separated by the Atlantic Ocean.

The Rocks Match Broad belts of rocks in Africa and South America are the same type. Broad rock belts in North America, the British Isles and Scandinavia match. These broad belts then match when the end of the continents are joined.

The Importance of Wegener’s Work Since Wegener's day, scientists have mapped and explored the great system of oceanic ridges, the sites of frequent earthquakes, where molten rock rises from below the crust and hardens into new crust. We now know that the farther away you travel from a ridge, the older the crust is, and the older the sediments on top of the crust are. The clear implication is that the ridges are the sites where plates are moving apart. Where plates collide, great mountain ranges may be pushed up, such as the Himalayas; or if one plate sinks below another, deep oceanic trenches and chains of volcanoes are formed. Earthquakes are by far most common along plate boundaries and rift zones: plotting the location of earthquakes allows seismologists to map plate boundaries and depths. Paleomagnetic data have allowed us to map past plate movements much more precisely than before. It is even possible to measure the speed of continental plates extremely accurately, using satellite technology. Nevertheless, Wegener's basic insights remain sound, and the lines of evidence that he used to support his theory are still actively being researched and expanded.

Links and Animations tmlhttp://library.thinkquest.org/17457/english.h tml Great site, Games and Activities o/animations/ch2.htm Fossil Animation

Key Terms for 7.1,7.2 and 7.3 Theory of Plate Tectonics Theory of Continental Drift Pangaea Crust, Mantle and Core Lithosphere Asthenosphere Convection Current Convergent Boundary Divergent Boundary Transform Boundary Subduction zone Mid-Ocean Ridge (Mid- Atlantic Ridge) Sea-Floor Spreading

QUIZ 1. Boundary where two plates move away from each other_____________ 2. Boundary where two plates move toward each other_________________ 3. Boundary where two plates move past each other ________________ 4. When two oceanic plates move away from each other it is called_______. 5. When an oceanic plate moves below a continental plate a_____zone is created. 6. The underwater chain of mountains in the Atlantic ocean caused by a divergent boundary is _____. 7. Theory that states that all of the continents were one large land mass millions of years ago is__________. 8. The theory that explains the movement of tectonic plates is_______. 9. The giant land mass that Wegener says existed millions of years ago is called________. 10. Made of crust and upper mantle_________. 11. Is made up of tectonic plates_________. 12. Consists of mantle, tectonic plates move on top of this_________. 13. A current of heat flows from the core to the crust. This movement of magma causes plates to move. _____________. 14. Outermost layer of the Earth_________. 15. Contains most of Earth’s mass___________. 16. Center of the Earth that is made mostly of iron and nickel___________.