Download
1 / 17
180 likes | 343 Views
Plate Tectonics and Continental Drift. Processes that renew and recycle the Earth’s crust. A review of the Earth’s structure. The Theory of Plate Tectonics. The theory was proposed by Alfred Wegener, a G erman scientist in the early 20 th century.
E N D
Plate Tectonics and Continental Drift Processes that renew and recycle the Earth’s crust.
The Theory of Plate Tectonics The theory was proposed by Alfred Wegener, a German scientist in the early 20th century.
The theory states that the Earth’s crust is broken into chunks called plates. The lithospheric plates move on convection cells in the mantle of the Earth. Mantle convection.
The place where plates meet are called “boundaries”. Plates can separate, collide or slide side to side
When ocean crust collides with continental crust, volcanic chains and deep sea trenches form. This collision causes subduction. Subducting (sinking) oceanic crust Island arcs form when oceanic crust collides with oceanic crust.
When continental crust collides with continental crust, mountain ranges are formed, like the Appalachians and the Himalayas. This is called mountain building. Over 71 million years, India drifted north and collided with Asia and formed the mountains called the Himalayas.
Plates separate where magma rises to the surface and spreads out in opposite directions. This creates a rift. This is how new seafloor or oceanic crust is created. The rift creating new seafloor is called the mid-ocean ridge or MOR. This process called seafloor spreading is the driving force moving the continents!
When plates slide side to side, they stick due to friction and then slip suddenly. The resulting slip is an earthquake. Earthquakes are some of the most destructive events resulting from plate tectonics. Tsunamis are ocean waves created by underwater earthquakes. Some are small. Some, like the tsunami that struck Thailand are very large.
Review Questions: What is the name of the theory that the Earth’s crust is broken into pieces called plates? What would scientists need in order to change the theory? Describe the three motions of the crustal plates. You observe new sea floor being made. What kind of plate boundary were you observing? You see mountains from an airplane. What kind of plate boundary were you observing? You are rattled by and earthquake. What kind of plate boundary were you observing? You are sailing around an island arc. What kind of plate boundary were you observing?
Part 2: Continental Drift Each year, the Earth’s continents move about the same distance that your fingernails grow if you didn’t cut them (don’t try this at home!). While it isn’t much, over millions of years the Earth’s surface changes over and over again.
Wegener could see the fit of the continents, but did not have a explanation for what would make continents move. Later, using his hypothesis, other scientists added new observations and other empirical evidence that supported the idea that a super-continent had once existed: Pangaea Earth model showing fossil evidence Puzzle Earth
After Mr. Wegener’s death, oceanographers discovered that the magnetic field of the Earth flop-flipped from time to time. Iron particles in new basalt formed at the MOR locked the iron particles in place, recording the magnetic field at the time the rock formed. This new evidence was strong support for continental drift, showing that the farther away from the MOR you go, the rock is older and matched by rock on the opposite side of the MOR.
Fossil evidence strongly supports the idea of a super continent. Fossils separated by oceans today, could have only formed if the continents were connected at some time in the past.
New information about the internal structure and movement of the mantle supported the idea of continental drift. Geologists sharedwhat they learned about seafloor spreading with paleontologists who studied fossils. This shared information support Wegener’s observation that the “puzzle Earth” was at one time a super continent, Pangaea.
Review Questions How is a model of the Earth showing where fossils formed useful in understanding changes in the Earth’s crust? Why are the fit of the continents and fossil evidence considered to be “empirical evidence”? How did magnetic stripes support the idea that the seafloor was spreading at the MOR? What did finding the same fossils in Africa, South America and Australia tell scientists about the connection of the continents? Do you think that the plates are still moving today? Explain why or why not. In the last slide, there are two images of the Earth. One is 250 million years ago and the other is 250 million years in the future. Which is which? Be prepared to defend you answer!
