Oceanic crust is mostly composed of ____________________.
basalt
A/An ____________________ ____________________ is a deep trough in the crest of many mid-ocean ridges.
rift valley
Beyond the Mid-Oceanic Ridge system are flat, level, featureless submarine surfaces called ____________________ ____________________.
oceanic island
Continental margins on both sides of the Atlantic Ocean are ____________________ ____________________ ____________________.
passive continental margin
A flat-topped seamount is called a/an ____________________.
guyot
A chain of volcanic islands that form along a subduction zone is called a/an ____________________ ____________________.
volcanic arc
A circular coral reef that forms a ring of island around a central lagoon is a/an ____________________.
atoll
California, Oregon, Washington, and western British Columbia were added to North America as ____________________ ____________________.
accreted terrane
Oceans cover about ____ percent of the Earth's surface
71
Oceanic crust is ____ than continental crust and therefore ____ isostatically.
denser, sinks
The average thickness of oceanic crust is about ____, whereas the average thickness of continental crust is about ____.
4-7 km, 20-40 km
The Mid-Oceanic Ridge rises high above the surrounding sea floor because new lithosphere forming at the ridge axis is ____ and of relatively ____ density.
hot, low
Most of layer 3 of the oceanic crust is composed of ____.
Gabbro
Rift valleys are characterized by ____ faults and ____ earthquakes
normal, shallow
Sand, silt, and clay that erodes from the continents and is carried to the deep sea floor is called ____.
terrigenous sediment
The flattest surfaces on Earth are ____.
abyssal plains
A/An ____ is a submarine mountain that rises 1 kilometer or more above the surrounding sea floor.
seamount
The age of the oldest ocean floor is about ____ million years.
200
The part of oceanic crust made up of pelagic and terrigenous sediment is ____.
layer 1
The Mid-Oceanic Ridge is composed mainly of:
basalt
Moving away from mid-ocean ridges, oceanic crust becomes:
older, sinks, and forms the abyssal plains.
The part of oceanic crust made up of pelagic and terrigenous sediment is:
layer 1
At sea-floor vents, bacteria produce energy from hydrogen sulfide in a process called:
chemosynthesis
If a series of island arcs collide with a continent over a long period of time, they add to a continent as:
accreted terranes
When two oceanic plates converge, the sinking plate drags the sea floor down to create:
an oceanic trench
Continental crust and oceanic crust firmly join together at a/an:
passive continental margin
An active continental margin forms:
where an oceanic plate sinks beneath a continental plate at a subduction zone.