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Earth in Action #2
| Term | Definition |
|---|---|
| Occurs at lower and cooler crustal levels... | brittle deformation |
| How does the strength of continental crust vary with depth? | at shallow levels of the crust, the rocks become stronger with depth deep in the crust, the rocks weaken and can flow in the solid state |
| What is the difference between a joint and a fault? | a fault displaces the rocks on one side relative to another |
| What type of stress could form the fault in this figure | horizontal compression |
| What type of stress is the cause of most folding? | compression |
| A shale is metamorphosed into three rock types: (1) a banded gneissic rock; (2) a rock with small mica crystals with a shiny aspect; (3) a very shiny rock with large mica crystals; and (4) a dull slate with cleavage. | 4, 2, 3, 1 |
| If a rock has both a foliation and lineation, what has probably happened to the rock? | it has been flattened and stretched while it was metamorphosed |
| Why could the geologic setting in this figure cause metamorphism | Because it forces rocks below the fault deeper as they are overridden |
| What is the typical relationship of cleavage to folds? | cleavage is usually parallel to the axial surfaces of folds |
| In what site on this figure would you expect high pressure-low temperature | A & B |
| What are the geologic features for which Siccar Point in Scotland is famous? | a boundary between steep gray layers below and gently dipping red layer above an unconformity an ancient erosion surface |
| If a rock started with 1,000 atoms of a parent but now contains 250 atoms, how many half lives have passed? | 2 half lives |
| What is a principle we use to determine the age of a landscape surface? | a surface with a well-developed soil is probably older than a surface with no soil |
| In this photograph, Paleozoic sandstone rests depositionally on Precambrian granite. What events must have occurred before deposition of the sandstone | uplift of granite to the surface solidification of granite at depth formation of an erosion surface |
| What factors are the most critical in determining whether a fossil is preserved? | whether the creature had hard parts and how fast it was buried |
| This figure shows two sections that partially overlap in age. Dashed lines show how the two sections correlate. What can you conclude from these correlations | the left section represents older rocks than the right section |
| What would fossil ages from the geologic timescale tell us about the age of this unconformity | is younger than the fossil ages on the tilted, older than the fossil ages in layers above the unconformitythe amount of time represented by the unconformity can be approximately bracketed by the ages of the fossils above and below |
| Which of the following is evidence that Earth's history is not short? | thousands of isotopic ages measured by different methods,4-billion-year age on a rock in Canada,rates of seafloor spreading compared to the width of the Atlantic Ocean,millions of layers of light- and dark-colored sediment that record yearly cycles |
| What was the Cambrian explosion? | a time when many different types of creatures appeared on Earth |
| What are some uses of magnetic reversals? | calculating rates of seafloor spreading,studying magnetic stripes on the seafloor,matching the patterns of reversals in a rock sequence to the magnetic time scale |
| Why are the patterns showing the age of the seafloor symmetrical in the Atlantic Ocean but not the Pacific Ocean? | subduction has consumed large areas of old oceanic crust in the Pacific,spreading along the Atlantic ridge added seafloor to plates on both sides |
| In the Atlantic Ocean, where is the oldest oceanic crust? | abyssal plain next to the continents |
| How do most oceanic islands and seamounts form? | they are constructed by volcanic eruptions that first occur under water |
| If you drilled into an oceanic plateau, what would you most likely find? | large amounts of basalt derived from melting in the mantle |
| What processes can occur in front of or behind some island arcs? | back-arc rifting,trench rollback |
| What is a popular model for the formation of an atoll? | a volcanic island forms and subsides |
| What causes the seafloor to deepen across a typical continental slope? | a transition from continental crust to oceanic crust,thinning of continental crust because of normal faults |
| If you were looking for graded beds, where would be a good place to start? | . in a submarine fan |
| What has happened to the Pacific Ocean in the last 200 million years? | it became smaller as the Atlantic Ocean opened |
| How can we tell that the Himalaya have been uplifted? | the top of Mount Everest contains a limestone with marine fossils,deep rocks are exposed at the surface and yield young isotopic ages,uplift can be measured with a global positioning system (GPS) |
| What could cause a region to be higher in elevation than an average part of a continent? | less dense continental crust |
| Which of the following is NOT a setting in which regional mountain belts form? | passive margin |
| Which of the following occurs when mountain belts are eroded? | deep metamorphic and plutonic rocks can be uplifted to the surface,the continental crust becomes thinner, erosion is accompanied by isostatic rebound |
| Which of the following is NOT a way in which local mountains can be built? | prolonged volcanism in composite volcanoes thrust faulting normal faulting folding |
| The basin shown in this figure was actively subsiding during the formation of unit: | C |
| Which of the following processes forms basins in an ocean-continent convergent boundary? | flexing of the continent by weight of the thrust sheets flexing and bending of the oceanic plate into the subduction zone |
| What can occur during the evolution of a hot spot? | formation of rifts that radiate out from the hot spot |
| What is the main reason why the age of oldest rocks can vary from one part of a continent to another? | parts of the continent have been added by the accretion of tectonic terranes |
| Seafloor spreading rates cannot be used to reconstruct past continents' positions older than 180 million years. Why? | oceanic crust older than 180 million years has been subducted and the record destroyed |
| Which of the following processes generates most earthquakes? | movement along faults |
| When do rocks along a fault have the highest amount of stress and stored elastic strain? | right before an earthquake |
| If an area has shallow, intermediate, and deep earthquakes, what can you infer about the area? | it is near a subduction zone,the shallow earthquakes will be closer to the trench than deeper ones, the depth pattern of earthquakes can be used to determine which way the slab is inclined,this area has the potential for large earthquakes |
| The characteristics of S-waves include: | they shear rock from side to side or up and down, they displace the rock in a direction that is perpendicular to their travel direction |
| How do we determine the location of a recent earthquake? | use seismic records from three or more stations |
| Shaking during an earthquake can: | liquefy unconsolidated sediments, causing destruction of buildings on top of ,generate a tsunami,trigger landslides,cause rigid buildings to collapse |
| The huge 1964 Alaskan earthquake, one of the largest earthquakes ever recorded, was caused by: | thrusting along a subduction zone (megathrust) |
| Sudden movement on a fault can cause a tsunami when: | the fault suddenly uplifts or downdrops the seafloor |
| Areas of high earthquake risk are mostly located: | near a boundary between tectonic plates |
| What is one way that we determine the depth to the base of the crust? | observing whether seismic waves that travel through the crust arrived after those that traveled through the mantle |
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