Deck 12: The Seafloor

Question 1

The Pacific, Atlantic, Arctic, and Indian Oceans form one interconnected ocean.

Answer 1

True

Question 2

The geologic margin of a continent is the land area outlined by sea level.

Answer 2

False

Question 3

The change from continental crust to oceanic crust occurs beneath the continental slope.

Answer 3

True

Question 4

The continental shelf is always very wide, extending tens to hundreds of kilometers seaward.

Question 5

The sediment accumulated on continental shelves consists of channel and floodplain deposits from a time when sea level was lower.

Question 6

Submarine canyons are eroded by turbidity currents.

Question 7

An active continental margin forms adjacent a spreading ridge as a new ocean is being created.

Question 8

Relative to an active margin, the continental shelf on a passive margin would be wider.

Question 9

Relative to an active margin, the continental slope along a passive margin descends directly into a trench.

Question 10

Abyssal plains tend to be most common seaward of passive continental margins.

Question 11

Rifting within continental crust is an important element in the initial development of an ocean.

Question 12

Oceanic ridges are fractured because cold water makes the rocks brittle and weak.

Question 13

Oceanic crust in trenches is cooler and show anomalously low heat flow.

Question 14

Earthquakes are deepest along oceanic trenches.

Question 15

Oceanic ridges are composed of a complex of both mafic and felsic rocks.

Question 16

Organisms living near submarine hydrothermal events thrive because of their ability to oxidize sulfur compounds.

Question 17

Coral reefs are present in any near-shore area with sufficient water quality to support corals and other forms of marine life.

Question 18

A linear succession of hot spot volcanoes may form an aseismic ridge.

Question 19

Guyots are flat-topped because submarine volcanic eruptions filled in their craters with lava.

Question 20

Some deep marine sediments are the result of viscous fluids oozing from marine organisms.

Question 21

Cosmic dust contributes a significant amount of sediment to the deep sea.

Question 22

Ophiolites are preserved sequences of oceanic crust that have not been subducted.

Question 23

The resources available within a country's Exclusive Economic Zone (EEZ) are the dissolved elements within seawater.

Question 24

Sand and gravel is one resource that is currently mined from the continental shelf.

Question 25

Until approximately 200 years ago the ocean floor was believed to be

A) unfathomable, stretching nearly to the center of Earth.
B) covered by sediments thousands of kilometers in thickness.
C) a flat featureless plain of sediments.
D) populated by sea monsters.
E) riddled with caverns extending to the center of Earth.

Question 26

The first true oceanographic expedition, in 1872, was conducted by the ship known as

A) Alvin.
B) H.M.S. Challenger.
C) JOIDES Resolution.
D) the Glomar Challenger.
E) H.M.S. Bounty.

Question 27

The topography of the ocean floor actually consists of

A) sediments only a few meters thick.
B) oceanic ridges and oceanic trenches.
C) thousands of submarine volcanoes dotting vast featureless plains.
D) ridges, trenches, hills, vast plains, plateaus, and volcanoes.
E) vast submarine chasms deeper, wider and longer than the Grand Canyon.

Question 28

Turbidity current deposits are

A) poorly sorted mixtures of mud and sand.
B) known as turbidites.
C) built-up to form submarine fans.
D) caused by slumps induced by earthquakes.
E) all of the above

Question 29

Continental shelves are widest when associated with

A) island arcs and volcanism.
B) an absence of volcanism and earthquakes.
C) intense earthquake activity.
D) active margins.
E) ocean trenches.

Question 30

Continental shelves are narrowest when associated with

A) an absence of earthquakes and volcanism.
B) regions where larger continents once rifted apart.
C) island arcs, volcanism and oceanic trenches.
D) passive margins.
E) submarine canyons.

Question 31

Which of the following are commonly associated?

A) island arcs and oceanic trenches
B) volcanic arcs and oceanic trenches
C) Benioff zones and volcanic arcs
D) oceanic trenches and active continental margins
E) all of the above

Question 32

Which of the following would NOT be found in deep ocean basins?

A) abyssal plains
B) oceanic ridges
C) coral reefs
D) oceanic trenches
E) B and C

Question 33

Black smokers and hydrothermal vents do NOT produce which of the following?

A) sulfur-rich water which supports unusual communities of chemosynthetic bacteria and previously unknown animals
B) mounds of black carbon and graphite brought up in solution from the basalt below
C) mounds of metal-rich sediments including iron, copper, zinc, silver and gold ores
D) pools of metal-rich brines
E) many of the worlds' deposits of ores within basaltic crust such as the Cyprus Troodos Massif

Question 34

Black smokers and hydrothermal vent communities were discovered by the submersible called

A) Kelvin.
B) Glomar Challenger.
C) Alvin.
D) H.M.S. Challenger.
E) JOIDES* Resolution.

Question 35

Calcareous pelagic ooze is composed mostly of

A) diatoms and radiolarians.
B) radiolarians and foraminifera.
C) foraminifera.
D) radiolarians and sponges.
E) reef rubble and foraminifera.

Question 36

Siliceous oozes are composed mostly of

A) sponges and alga.
B) diatoms (animals) and radiolarians (animals).
C) diatoms (plants) and radiolarians (animals).
D) volcanic ash and cosmic dust.
E) diatoms and foraminifera.

Question 37

Reefs are

A) mound-like, wave-resistant structures composed of coral.
B) found in warm water, both shallow and deep.
C) mound-like, wave-resistant structures composed of skeletons.
D) found throughout the world in shallow and deep water.
E) large rocks projecting from deep water into shallow water.

Question 38

The continental shelf encompassed by the EEZ produces

A) 27% of the oil and gas produced by the U.S.
B) 17 % of the oil and gas produced by the U.S.
C) 10 % of the oil and gas produced by the U.S.
D) 7 % of the oil and gas produced by the U.S.
E) 1.7% of the oil and gas produced by the U.S.

Question 39

Among the mineral resources NOT found in deep sea sediments are

A) manganese nodules.
B) sand and gravel.
C) reef rock.
D) iron, copper, and zinc.
E) silver and gold.

Question 40

The EEZ contains over 30 sedimentary basins, some of which are known to contain

A) hydrocarbons.
B) precious metals.
C) sulfide metals.
D) manganese nodules.
E) tar sands.

Question 41

The name of the first research vessel to drill into the sea floor, in 1968, to extract cores of sediment and crust was the ___________ ___________.

Question 42

Zones separating the part of a continent above sea level from the deep sea floor are known as___________ ___________ .

Question 43

The___________ ___________ is the deeper, gently-sloping sea floor, seaward of the___________ ___________ .

Question 44

___________ ___________ that are turbulent and sediment-laden and proceed by gravity flow through submarine canyons from the continental slope to the continental rise.

Question 45

Turbidity current sediments are generally deposited on the ___________ ___________ .

Question 46

The flat surfaces covering vast areas of deep ocean basins are ___________ ___________.

Question 47

___________ ___________ long, deep, narrow features on the sea floor, restricted to active continental margins

Question 48

Oceanic ridges are composed of___________ .

Question 49

The United States claimed sovereign rights over an area that extends 200 nautical miles from the coast known as the ___________ ___________ ___________ .

Question 50

___________ ___________ are chimney-like hydrothermal vents which contain water with high concentrations of metals dissolved from the basalt below.

Question 51

A___________ reef is one that is solidly attached to the margins of an island or continent, while a ___________ reef is separated from a landmass by a lagoon.

Question 52

What is the geological evidence indicating that Earth had an ocean and atmosphere 3.5 billion years ago?

Question 53

Briefly explain how atoll reefs develop.

Question 54

Explain how hydrothermal vents produce mounds of ore-rich sediments.

Question 55

How do geologists know what rock types underlie sheeted basalt dikes if the ocean crust has not be drilled to the depth at which they occur?

Question 56

How does upwelling exemplify a system?

Question 57

Why is upwelling such an important process relative to fisheries?

Question 58

Who is considered the source of the original two written descriptions of the Atlantis legend?

Question 59

What is the scientific evidence against the existence of a sunken continent of Atlantis?

Question 60

What do some archaeologists believe the legend of Atlantis actually describes?

Question 61

What was the most probable origin of Earth's ocean and atmosphere?

Question 62

What are some of the modern techniques that are used in oceanographic research?

Question 63

When did concerted research on the ocean floor begin, from which most of our knowledge about the sea floor has been obtained?

Question 64

What are the components of the continental margin, from sea level toward the ocean basin?

Question 65

What is the geological boundary of a continent?

Question 66

Briefly explain why some deep sea deposits have graded bedding form.

Question 67

Briefly explain why the origins of some submarine canyons are not fully understood.

Question 68

What two types of continental margins are generally recognized?

Question 69

What is an example of a passive margin, in the Western hemisphere?

Question 70

What is an example of an active margin, in the Western hemisphere?

Question 71

When present, the abyssal plains are always adjacent to which part of the continental margin?

Question 72

What are some of the characteristics of oceanic trenches?

Question 73

What is a Benioff zone?

Question 74

How long is the oceanic ridge system of which the Mid-Atlantic Ridge is a part?

Question 75

What are some of the characteristics of oceanic ridges?

Question 76

What is the origin of seamounts, guyots, and aseismic ridges?

Question 77

What is an aseismic ridge?

Question 78

What is a guyot?

Question 79

What causes submarine hydrothermal vents?

Question 80

Where, on the sea floor, do submarine hydrothermal vents occur?