Oceanography Concept Questions Chapter 3

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3. What force did Wegener believe was responsible for the movement of continents?

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Wegener believed that the heavy continents were slung toward the equator on the spinning Earth by a centrifugal effect. He was wrong in that belief, but correct in sensing that continents were moving.

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2. What were the greatest objections to Wegener's hypothesis?

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Where were the tracks through old seabed that the migrating continents might leave? What forces were strong enough to propel continents over long distances?

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EARTH'S INTERIOR IS LAYERED

3.What do we mean when we say something is dense?

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Something is said to be dense if it weighs a lot per unit of volume. Density is an expression of the relative heaviness of a substance.

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EARTH'S INTERIOR IS LAYERED
4. How is density expressed (units)?

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Density is usually expressed in grams per cubic centimeter (g/cm3)........NOTE-(the (3) is spoused to be up higher and smaller..) Nicholas couldn't figure out how to do that one on the computer and is a little to lazy at the moment ;)

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EARTHS INTERIOR IS LAYERED
5. Has anybody drilled into Earth's densest interior layers?

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No one has yet sampled below Earth's outermost layer, the crust.

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THE STUDY OF EARTHQUAKES PROVIDES EVIDENCE FOR LAYERING
6. What are the two kinds of seismic waves? Which causes most of the damage in an earthquake? Which are the most useful in determining the nature of Earth's interior?

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Seismic waves form in two types: surface waves and body waves. Surface waves can sometimes be seen as an undulating wave-like motion in the ground. Surface waves cause most of the property damage suffered in an earthquake. Body waves (P waves and S waves) are less dramatic, but they are useful for analyzing Earth's interior structure.

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THE STUDY OF EARTHQUAKES PROVIDES EVIDENCE FOR LAYERING
7. Differentiate between P waves and S waves. Which can go through fluids? Through solids? How are "shadow zones" related?

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The P wave (or primary wave), is a compressional wave similar in behavior to a sound wave. Rapidly pushing and pulling a very flexible spring (like a Slinky) generate P waves. The S wave (or secondary wave) is a shear wave like that seen in a rope shaken side to side.

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THE STUDY OF EARTHQUAKES PROVIDES EVIDENCE FOR LAYERING
8. How did the 1964 Alaska Earthquake enhance our understanding of Earth's interior?

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The P and S waves from Alaska were very large and easily detected at great distances. When correlated with the frequency, intensity, and phase characteristics of the waves, this information helped to confirm the models of Earth layering.

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EARTH'S INNER STRUCTURE WAS GRADUALLY REVEALED

9.How are Earths inner layers classified?

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Earth's layers are classified by composition and by physical properties. Understanding the physical properties of the layers is important in understanding tectonic processes.

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EARTH'S INNER STRUCTURE WAS GRADUALLY REVEALED
10. What's the relationship between crust and lithosphere? Between lithosphere and asthenosphere?

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Lithosphere includes crust (oceanic and continental) and rigid upper mantle down to the asthenosphere. Note that the rigid sandwich of crust and upper mantle-thelithosphere-floats on (and is supported by) the denser deformable asthenosphere.

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EARTH'S INNER STRUCTURE WAS GRADUALLY REVEALED
12.How can something as heavy as a continent be so high? The Himalayas are more than 8,800 kilometers (29,000 feet) high-what holds them up there?

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A continent floats above sea level because the lithosphere gradually sinks into deformable asthenosphere until it has displaced a volume of asthenosphere equal in mass to the continent's mass. Because granite is comparatively light, the top of the continent can float high above sea level.

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EARTHS INNER STRUCTURE WAS GRADUALLY REVEALED
11. Which part of Earth's interior is thought to be a liquid.

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The outer core is thought to be liquid.

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THE NEW UNDERSTANDING OF EARTH EVOLVED SLOWLY
13.Why is the inside of Earth so hot?

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Much of the heat inside Earth results from the decay of radioactive elements.

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THE NEW UNDERSTANDING OF EARTH EVOLVED SLOWLY
14. How does heat move from the inner Earth to the surface?

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Some of the internal heat journeys toward the surface by conduction-the same process that makes a frying pan's handle hot.

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THE NEW UNDERSTANDING OF EARTH EVOLVED SLOWLY
15. Why were traditional views of the age of Earth an impediment to early understanding of Earth's inner structure?

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Understand Earth's age was hampered by an interpretation of the biblical account of creation. At the end of the eighteenth century most European natural scientists believed in a young Earth, one that had formed only about 6,000 years ago. Since believed in a young Earth, one that had formed only about 6,000 years ago. Since many of the processes observed on Earth had clearly operated for much greater spans of time, confusion was understandable.

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WEGENER'S IDEA IS TRANSFORMED
16. How did a careful plot of earthquake locations affect the discussion of the Theory of Continental Drift (as it was first called)? What about the jigsaw- puzzle- like fit of continents around the Atlantic?

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The jigsaw-puzzle fit of continents around the Atlantic and the distinctly non-random distribution of earthquakes stimulated vigorous discussion in geological circles. Hugo Benioff's plots of earthquake activity surrounding the Pacific Ring of Fire demanded explanation, and researchers redoubled their efforts to discover the links after the conclusion of the Second World War.

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WEGENER'S IDEA IS TRANSFORMED
17. How did an understanding of radioactive decay and radiometric dating influence the debate?

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Radiometric dating allowed rock sequences to be dated and their relative positions through time determined. Radiometric studies also solidified understaning of Earth's age, assuring researchers that Earth was indeed older than 6,000 years and that time was sufficient for large-scale seafloor spreading.

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What was the key insight that Hess and Wilson brought to the discussion?

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CONVECTION CURRENS. In 1965 John Tuzo Wilson integrated the ideas of continental drift and seafloor spreading into the overriding concept of plate tectonics.

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Can you outline- in very simple terms-theaction of Earth's crust described by the theory of plate tectonics?

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Look up figure 3.37

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20. What kind of plate boundaries exist?

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The three types of plate boundaries that result from these interactions are called divergent, convergent, and transform boundaries,depending on their sense of movement

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21. What happens at each of the plate boundaries..?

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Ocean basins are formed at divergent plate boundaries;island arcs form, continents collide, and crust recycles at convergent plate boundaries; crust fractures and slides at transform plate boundaries.

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22. About how fast do plates move?

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Through spreading speeds can reach a rate of 18 centimeters (7 inches) a year along parts of the pacific plate, most plates move more slowly, about 3 centimeters (1.3 inches) each year.

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23. Which kind of plate movement is related to earthquakes and tsunami?

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A subducting plate's periodic downward lurches cause earthquakes and tsunami.

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24. Is Earths magnetic field a constant? That is, would a compass needle always point north? how can Earths magnetic field by frozen into rocks as they form?

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Earths magnetic field reverses at irregular intervals of a few hundred thousand years. In a time of reversal a compass needle would point south instead of north, and any particles of magnetic material falling below their curie points in fresh seafloor basalt at a spreading center would be imprinted with the reversed field.

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25. Can you explain the matching magnetic allignments seen south of iceland?

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The alternating magnetic stripes represent rocks with alternating magnetic polarity-one band having normal polarity (magnetized in the same direction as todays magnetic field direction) and the next band having reversed polarity (opposite from todays direction.) Researchers realized that the pattern of alternating weak and strong magnetic fields was symmetrical because freshly magnetized rocks born at the ridge are spread apart and carried away from the ridge by plate movement.

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26.What is a hot spot? where can you go to see hot spot activity?

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Hot spots are one of the surface expressions of plumes of magma rising from relatively stationary sources of heat in the mantle. My favorite hot spot is iceland, but the island of Hawaii is a close second.

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27.How does the long chain of Hawaiian volcanoes seem to confirm the theory of plate tectonics?

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The northern pacific contains an "assembly line" chain of islands which extends from the old eroded volcanoes of the emperor seamounts to the still glowing island of Hawaii. The pacific plate is moving northwest relative to a mantle plume anchored in the mantle below.

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28.Earth is 4,600 million years old, and the ocean is nearly as old. Why is the oldest ocean floor so young- rarely more than 200 million years old?

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Subduction guarantees young seafloors. Consider the pacific: new seabed is made at the east of Pacific rise, transits to the northwest, and disappears in the trenches seaward of the Aleutian Islands and Japan. This process takes less than 200 million years, so the seabed and its sediments are always young.

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29. Do you live on a terrane?

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You might live on a terrane. if you live in western North American, check figure 3.35

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30.Can you suggest areas for future research in plate tectonics?

Back 30

A review of the bulleted list in this section will provide you with these answers.. LOOK IT UP NICK!

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31. In your opinion, how has an understanding of plate processes revolutionized geology?

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It's difficult to underestimate the effect our understanding of plate tectonics has had on all areas of science. Coal in the Antartic? Latitudinal variations in the Australian barrier Reef? Similar fossils across seperated continents? the relative youth of the seabed? Earthquake distribution (and prediction)? its hard to know where to stop!