“Continental Drift and Plate Tectonics Study Guide”

ANSWERS:

1. Explain 4 types of evidence that Alfred Wegener used to explain continental drift. Some continents look like they fit together (example- S. America & Africa), Geological Clues (Ex. Mountain Belts lined up in North America & Europe),Fossil Clues (Ex. Mesosaurus found in S.America & Africa. Glossopteris found in S. America, India, Africa, & Antarctica),Climate Clues (Glacial deposits in tropical regions like India and Australia.)

2. Completely explain seafloor spreading and how scientists know it is happening. The theory states that magma travels to the earth’s surface.

The magma forms cracks in the ocean floor.

The magma pushes out of the cracks.Magma piles up and forms mid-ocean ridges.As the magma hardens it pushes the layers of the ocean floor away from the mid-ocean ridge.The process then repeats it self.

Proof- The existence of pillow lava (on sea floor), the oldest layers of the Atlantic Ocean floor are on the coastline of the continents. (180 million years old.) The youngest layers of the Atlantic Ocean floor are in the center of the ocean (50 million years old). Magnetic reversals can also be used as seafloor spreading proof. Every 200,000 years or so, the earth’s poles reverse. During those times any rock that forms will have a record of what the polarity was at that time. Since the polarity of the rock that makes up the ocean floor changes, the ocean floor rock must have formed at different intervals. This would have moved the existing rock away from the center as new rock formed. If seafloor spreading did not take place the whole ocean floor would have the same polarity.

3. Completely explain what plate tectonics is and how it works.

Plate tectonics is the theory that earth’s lithosphere is broken into sections, called plates, that slowly move around on the asthenosphere. Convection of magma is the driving force that makes the plates move. Material close to the core is hot and has a low density. Material close to the surface is cooler and has a high density. The more dense material sinks and the less dense material rises. Because magma is sticky, when the magma reaches the plates it pushes or pulls the plates toward or away from a boundary.

4. Why do plates move?

Plates are less dense than the asthenosphere is. This allows them to float on top of the asthenosphere and be moved easily by the sea-floor spreading and (convection currents).

5. Why does earth have land features like the ones we talked about in class?

Volcanoes can be found at any divergent boundary, an ocean-ocean plate convergent boundary, and a continental plate ocean plate convergent boundary. Mountains form when two continental plates collide. Neither plate is dense enough to sink so you do not have any eruptions. A rift valley forms when any two plate separate. 2 other features are found inside of a rift valley. Volcanoes can be found there due to the rising magma. Ridges or mid-ocean ridges could also be found there due to the magma coming out of the ocean floor cracks. Trenches form at the base of a continental ocean plate boundary and an ocean plate ocean plate boundary because the more dense plate of the two sinks forming a deep v-shaped valley.

6. What are the layers of the EARTH and how are they different fromone another? Are any of them similar?Earth has 4 basic layers, crust, mantle, the outer and inner cores. Specific sub-layer would be the lithosphere (crust and topmost mantle) and the asthenosphere (upper mantle). Each layer has differing densities, temperatures and thicknesses. Most layers have slightly different compositions, though some elements are found throughout all the layers. These elements would be similarities. Also the fact that all layers are fairly solid except for the outer core.

  1. How we know how deep layers are and what they are made of if we have never been there? What is the *Mohorovicic discontinuity? Scientists have used 2 types of evidence to learn about the Earth’s interior, rock samples (direct evidence) and seismic wave behavior(indirect evidence). Drilling holes and look at samples and studying cooled magma from the interior helps scientists determine the make up of the interior. Scientists observe the waves generated by earthquakes. They study the changes in speed and path of the waves as they travel through the interior and can determine differing densities and compositions and certain depths. The "Moho", is the boundary between the crust and the mantle---The Mohorovicic Discontinuity marks the lower limit of Earth's crust. At this depth seismic waves change velocity. At this discontinuity, seismic waves accelerate due to density increase of the material.