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26 Cards in this Set
- Front
- Back
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On what points was Wegener correct? Wrong? |
Wegener was correct about the fact that continents were moving in a drifting like pattern but he didn't have a method for how this was happening. Wilson pulled all the knowledge from Wegener and many others and came up with the method of convection for the plates to move. |
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How are Earth's internal layers classified? |
Earth's internal layers are classified chemically (crust, mantle, outer core, inner core) and physically (lithosphere, asthenosphere, mesosphere, core) |
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How is crust different from lithosphere? |
Crust is a part of the lithosphere. They re both rigid and 'cold' and float on top of the asthenosphere. The only difference is that the lithosphere also houses the upper mantle in it's classification. |
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Where are the youngest rocks in the seabed? The oldest? Why? |
The youngest rocks in the seabed are located at the spreading centers of the ocean because new magma continuously forces its way up to the surface and becomes new basaltic oceanic crust. Therefore, the oldest rocks in the seabed are the furthest away from the spreading centers landing them straight smack dab at the bottom of ocean trenches where subduction is slowly pulling them down and away. |
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Would the most violent earthquakes be associated with spreading centers or with subduction zones? Why? |
The most violent earthquakes would be associated with subduction zones because along a subduction zone there is a lot of surface area rubbing on the subducting plate. Each time the plate lurches downwards to get recycled, an earthquake occurs. The further the plate lurches down the more violent the quake. |
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Describe the mechanism that powers the movement of the lithospheric plates. |
The lithospheric plates are powered by the Wilson cycle that states that the mantle is heated, becomes less dense, pushes up (at spreading centers) and distributes to either side under neath the plates. This pushes the plates away from the spreading centers. The convection current then continues until it cools, becomes more dense and helps pull the subjecting side of the plate downwards, and starts the cycle all over again. |
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Why is paleomagnetic evidence thought to be the 'lynchpin' in the plate tectonics argument? Can you think of any objections to the Matthews/Vine/Morley interpretation of the paleomagnetic data? |
paleomagnetic evidence was found along the spreading centers in bands of varying magnetism (directions). This paleomagnetic banding showed when the poles flipped, and since they were the same on both sides of the spreading centers, it backed up the theory of plate tectonics by proving that the plates moved away from each other. Some objections would be that maye the sediment is just building in waves on top of each other like a volcano, or that a different phenomenon is occurring entirely to crate the banding. |
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What biological evidence supports plate tectonic theory? |
fossil records show regions (when the continental re placed into a mass continent Pangaea) that are continuous through the continents when placed together like a puzzle, however now they are on completely different parts of the world which suggests that the continents where once a part of a larger continent. We also can see biogenies evidence that shows the movement of the sediment away from the spreading centers into depths where they wouldn't otherwise be found. |
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What evidence can you cite to support the theory of plate tectonics? What questions remain unanswered? Which side would you take in a debate? |
Evidence such as the paleomagnetism, fossil records, earthquake maps, etc...There are many questions that remain such as why exactly one plate subducts under another and why the continents were so close to begin with for Pangaea, and how did it all start moving. I would take the side of doubting all of the evidence because it would be more fun to try and stump those that believed in plate tectonics. |
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Why are the continents about 20 times older than the oldest ocean basins? |
The continents are 20 times older than the oldest ocean basin because the continents are not as dense as the oceanic plates so they don't subduct when a continental plate and an oceanic plate collide. Therefore, with the oceanic plates always subducting the ocean has relatively new dating yet the continent has very old rocks. |
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Why did people think an ocean was deepest at its center? What changed their minds? How is modern bathymetry accomplished? |
People thought that the ocean was deepest at its center because they noticed that the further out they got the deeper the ocean generally was. The thing that changed their minds was the single beam sonar that was able to measure the depth of the ocean without needing a winch and weight or stone and rope. This way they were able to do a contour across the atlantic ocean or any ocean for that matter. They found out that the trenches were the deepest and the mid-ocean ridges actually made the middle of the ocean not as deep as they once thought. Today, we either use multi beam sonar, which sends out multiple beams of frequency, and we also use satellites that measure the changes in the surface of the ocean. |
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draw a rough outline of an ocean basin. Label the major parts. Which is greater: the average height of the continents above sea level or the average ocean depth? |
shelf, shelf break, slope, rise, abyssal plain. The average height of the continents is nowhere near the average depth of the ocean. |
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What do the facts that granite underlies the edges of continents and basalt underlies deep-ocean basins suggest? |
the fact shows that granite had a different origin than the spreading center creation of the basaltic ocean crust. Granite is mostly sediment deposits that have been lithified and it is nowhere near as dense as the basalt. However it is much thicker due to it riding higher on the lithosphere and having billion years to accumulate. |
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The terms leading and trailing are also used to describe continental margins. How do you suppose these words relate to active and passive, or atlantic-type and pacific-type used in the text? |
The leading edge of the continent is the part that is closest to a subduction zone, this is also called an active boundary because the subduction zone is right there. In other words, it's a pacific-type boundary because a plate is subducting. The opposite is true of a trailing edge of a continent. it has a passive boundary because tectonic plates are not being destroyed and is typically on the atlantic side of the continent, also known as an atlantic-type boundary. |
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What part of the seabed is richest in petroleum and natural gas? Why do you suppose it is there and not somewhere else? |
Usually on the continental shelf we can find petroleum deposits due to sedimentation s form the continent, therefore, similar deposits would be found in relatively shallow areas in the ocean where deposition occurs. |
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Why are abyssal plains relatively rare in the Pacific? |
Abyssal plains are relatively rare in the pacific because in order to create these relatively flat expanses you need sedimentation to cover the oceanic ridges which there isn't enough as the sediments from the continents go into the trenches not onto continental rises where turbidity currents occur. |
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In what ways are sediments classified? |
Sediments are classified by their size, andif they are poorly-sorted or well-sorted deposits and another method is their origin. |
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List the four types of marine sediments. Explain the origin of each. |
The main marine sediments are terrigenous, biogenies, hydrogenous, and cosmogonies. Terrigenous is sourced from land erosion which is then deposited into the ocean; biogenies is from certain silica based and calcium based animals that create shells out of the materials that eventually fall to the sea floor; hydrogenous which form from chemical processes in the ocean, and finally cosmogonies which comes from extraterrestrial dust and comets. |
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How are neritic sediments generally different from pelagic ones? |
Neritic sediments are mostly terrigenous based sediments that are from the continental shelf or the continent itself whereas pelagic sediments are from the ocean basin either by biogenies or hydrogenous sediment creation. |
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Is the thickness of ooze always an accurate indication of the biological productivity of surface water in a given area? |
The thickness of ooze is not always an accurate indication of the biological productivity of the surface water because ooze cannot form past a certain depth in the ocean called the calcium carbonate compensation depth (also siliceous depth as well) where the shells that the organisms usually drop to create the ooze disintegrate and don't exist past the CCD line. The ocean could be teaming with activity above an yet show nothing of that activity below because of the depth and acidity of the ocean. |
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What happens to the calcium carbonate skeletons of small organisms as they descend to great depths? How do the siliceous components of once-living things compare? |
When the skeletons of calcium carbonate based small organisms descend to greater depths the ocean becomes more acidic due to less oxygen and more pressure. Between those two factors and a few others, the calcium carbonate breaks down. Siliceous organisms can withstand most of the acidity and pressure but once they reach a much lower depth even they break down as well. |
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What sediments accumulate most rapidly? Lease rapidly? |
Terrigenous and biogenous accumulate the most rapidly due to the most sources for the sediment to be deposited from. Cosmogonies and hydrogenous accmulate the least rapidly because they either a) take a long time to react into the sediments or b) take a long time to accumulate anything. |
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Can marine sediments tell us about the history of the ocean from the time of its origin? Why? |
Marine sediments cannot tell us about the history of the ocean from its origin because the ocean floor dates only to 200 million years old whereas the earth and the formation of the crust and subsequently the ocean formed around 4.6 billion years ago. |
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How do paleoeanographers infer water temperatures, and therefore terrestrial climate, from sediment samples? |
They infer water temperatures as well as terrestrial climate by using the amount of biogenies sediments in cores. We know the conditions it takes for the organisms that create the ooze to be prosperous or not so we can then infer by the amount of sediment deposit the temperatures of the ocean and therefore the terrestrial climate as well. |
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Where are sediments thickest? Are any areas of the ocean floor free of sediments? |
Sediments are thickest in the Atlantic on the continent's trailing edge that's furthest away rom the spreading center. There are ocean floors that are free of sediments but they are far and few between. They are located directly at the spreading centers where new ocean floor is constantly being created. There, there is not enough time yet for sediment to accumulate and is therefore free, or almost entirely free of sediment. Also where strong currents are present. |
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Why doesn't the sediment record extend back to the time of the origin of the ocean? |
The sediment record doesn't extend back to the 4.6 billion years of earth's history and it's creation because the dense, ocean plates that accumulate millions of years worth of sediment are always being subducted beneath a continental or another oceanic plate due to their density. The greatest time span that we have is around 200 million years back, and those sediments are found at the bottom of the trenches near subducting plates. |
