Question 1

How were water depths and seafloor bathymetry (submarine topography) determined by the Challenger surveys?

Accepted Answer

The Challenger surveys, conducted in the 1870s, determined water depths and seafloor bathymetry using hand-thrown and retrieved weighted lead-lines, a method where a rope with a weight was lowered to the seafloor to measure depth.

Question 2

What geologic studies finally confirmed Darwin's hypothesis that coral atolls all had a volcanic substrate underneath that formed the original platform for corals to colonize?

Accepted Answer

The scientific drilling of Eniwetok and Bikini Atolls by the U.S. government in preparation for nuclear weapons tests provided direct evidence supporting Darwin's hypothesis that coral atolls are built on volcanic substrates. This drilling allowed scientists to directly observe the volcanic rock beneath the coral layers, confirming the foundational role of volcanic activity in atoll formation.

Question 3

Seafloor spreading occurs along relatively narrow areas at the crests of oceanic ridges called__________

Accepted Answer

Seafloor spreading occurs along rift zones, which are narrow areas at the crests of mid-ocean ridges where new oceanic crust is formed through volcanic activity and gradually moves away from the ridge, creating new seafloor.

Question 4

The________ lies at the base of the continental slope.

Accepted Answer

The continental rise lies at the base of the continental slope, transitioning between the slope and the abyssal plain.

Question 5

Which one of the following did not accompany the 1929 Newfoundland ML 7.2 earthquake?

Accepted Answer

The 1929 Newfoundland ML 7.2 earthquake was accompanied by a tsunami, turbidity currents that broke submarine telegraph cables, but there was no explosive volcanic eruption of pillow basalts associated with it.

Question 6

What sedimentary process is mainly responsible for the accumulation of up to 9 kilometres of sediment in deep ocean trenches?

Accepted Answer

Turbidity currents and submarine landslides from the continental slope and trench walls are primarily responsible for the accumulation of significant amounts of sediment in deep ocean trenches. These processes transport sediments from shallower areas to the deep ocean, contributing to the thick sediment layers found in these regions.

Question 7

Calcareous ooze is composed of___________ sediment.

Accepted Answer

Calcareous ooze is composed of biogenous sediment, which is formed from the accumulation of the hard parts of microscopic organisms living in the ocean.

Question 8

Below the coral limestone, surface rocks of an atoll, what would you find?

Accepted Answer

Atolls form from the growth of coral reefs around a sinking volcanic island. As the island erodes and subsides, the coral continues to grow upwards, maintaining its position at the sea surface, which eventually results in the formation of an atoll. Below the coral limestone and surface rocks of an atoll, you would find the basaltic volcanic rocks of the original volcanic island, now a truncated seamount.

Question 9

__________develop where oceanic lithosphere bends downward and sinks into the mantle.

Accepted Answer

Deep ocean trenches form where oceanic lithosphere bends downward and sinks into the mantle, a process associated with subduction zones.

Question 10

What thicknesses of unconsolidated sediment typically covers the deep abyssal plains?

Accepted Answer

The answer of What thicknesses of unconsolidated sediment typically covers...

Question 11

_______is/are not part of an ophiolite complex.

Accepted Answer

Ophiolite complexes typically include sections of the Earth's oceanic crust and the underlying upper mantle, which have been uplifted and exposed above sea level. They often consist of mafic and ultramafic rocks such as gabbro (A), basaltic lavas including pillow lavas (B), and sheeted dyke complexes (D). However, enriched, unmelted, unstrained mantle lithosphere (C) is not considered a part of the ophiolite sequence, as ophiolites represent sections of the oceanic crust and upper mantle that have undergone partial melting and tectonic emplacement onto continental crust.

Question 12

Which ocean floor sediment type includes quartz sand?

Accepted Answer

Terrigenous sediments are derived from land and often include materials like quartz sand, which are transported to the ocean by rivers, wind, glaciers, and gravity flows.

Question 13

If you are sailing across the continental shelf in Queen Charlotte Sound and your echo sounder reported the bottom at 200 milliseconds (0.200 sec) at the maximum depth crossing the axis of Mitchell Trough, how deep is the seabed in the middle of this drowned submarine valley? Use the equation: depth (m) = 0.5 * (1500 m/s * total 2- way travel time in sec)

Accepted Answer

The depth is calculated using the formula: depth = 0.5 * (1500 m/s * 0.200 sec) = 150 m.

Question 14

How broad an area of seafloor was covered by the 1929 Grand Banks turbidite deposit?

Accepted Answer

The answer of How broad an area of seafloor was...

Question 15

Satellites like SEASAT can observe the ocean using to________ measure sealevel to +/- 2 cm and infer the seabed bathymetry from the __________exerted by the variable elevation and mass of seabed features.

Accepted Answer

Satellites like SEASAT use microwave beams to measure sea level accurately and can infer seabed bathymetry based on the gravitational pull exerted by the variable elevation and mass of seabed features.

Question 16

How do calcareous oozes form?

Accepted Answer

Calcareous oozes form primarily from the accumulation of calcium carbonate shells and skeletons of marine organisms. These organisms, such as foraminifera and coccolithophores, live in warm, surface waters. After these organisms die, their calcareous parts sink to the ocean floor, forming ooze. This process does not involve precipitation in the water column below the depth of sunlight penetration, turbidity currents, or the action of deep-ocean bacteria.

Question 17

Which is the best description of a mid- ocean ridge?

Accepted Answer

Mid-ocean ridges are characterized by their wide, block-faulted regions of basaltic seafloor, which are elevated above the surrounding abyssal plains, fitting the description in choice C.

Question 18

Which ocean floor sediment type includes diatom ooze?

Accepted Answer

Diatom ooze is a type of biogenous sediment, meaning it is made up of the remains of living organisms, in this case, diatoms, which are a type of algae.

Question 19

What sedimentation rates typify the red or brown clays of the abyssal plains?

Accepted Answer

Sedimentation rates for the red or brown clays of the abyssal plains are very slow, typically around 1 centimetre per 5,000 to 50,000 years. This slow accumulation is due to the vast distance from continental sources of sediment and the dominance of very fine particles that settle slowly through the ocean water.

Question 20

What is meant by graded bedding?

Accepted Answer

Graded bedding refers to a sedimentary layer that shows a gradual change in grain or clast size from the bottom to the top of the bed. This typically occurs as a result of a decrease in energy in the depositional environment, allowing larger particles to settle out first, followed by progressively finer materials.

Quiz 2: Minerals: the Building Blocks of Rocks