Earth Science Chapter 15
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Oceans cover about ____ percent of the Earth's surface.
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71
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Oceanic crust is ____ than continental crust and therefore ____ isostatically.
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denser, sinks
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The average thickness of oceanic crust is about ____, whereas the average thickness of continental crust is about ____.
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4-7 km, 20-40 km
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The depth of the central parts of the ocean basins is about ____ kilometers.
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5
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The Mid-Oceanic Ridge rises high above the surrounding sea floor because new lithosphere forming at the ridge axis is ____ and of relatively ____ density.
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hot, low
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Most of layer 3 of the oceanic crust is composed of ____.
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gabbro
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Rift valleys are characterized by ____ faults and ____ earthquakes.
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normal, shallow
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Sand, silt, and clay that erodes from the continents and is carried to the deep sea floor is called ____.
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terrigenous sediment
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The flattest surfaces on Earth are ____.
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abyssal plains
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A/An ____ is a submarine mountain that rises 1 kilometer or more above the surrounding sea floor.
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seamount
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A circular coral reef that forms a ring of islands around a central lagoon is a/an ____.
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atoll
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The age of the oldest ocean floor is about ____ million years
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200
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The part of oceanic crust made up of pelagic and terrigenous sediment is ____.
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1 layer
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Island arcs grow from ____.
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submarine volcanoes near a subduction zone
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Submarine canyons on continental shelves and slopes are cut by ____.
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turbidity currents
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Most of the water that fills the Earth's oceans came from:
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interplanetary space
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Samples can be taken from the deep sea floor by:
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coring devices
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Remote sensing devices used to study the ocean floor are:
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all of these
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A magnetometer could be used to:
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determine the orientation of the Earth's magnetic field at the time the mineral cooled
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The Mid-Oceanic Ridge is composed mainly of:
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basalt
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Moving away from mid-ocean ridges, oceanic crust becomes:
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older, sinks, and forms the abyssal plains
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The part of oceanic crust made up of pelagic and terrigenous sediment is:
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layer 1
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At sea-floor vents, bacteria produce energy from hydrogen sulfide in a process called:
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chemosynthesis
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If a series of island arcs collide with a continent over a long period of time, they add to a continent as:
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accreted terranes
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When two oceanic plates converge, the sinking plate drags the sea floor down to create:
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an oceanic trench
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Continental crust and oceanic crust firmly join together at a/an
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passive continental margin
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The continental rise on a passive continental margin is a/an:
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apron of terrigenous sediment that was transported across the continental shelf and deposited on the deep ocean floor at the foot of the continental slope
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An active continental margin forms:
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where an oceanic plate sinks beneath a continental plate at a subduction zone
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An oceanic island:
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is a seamount that rises about sea level
