OCE Exam 1 (NOT INCLUDING GRAPHICS)

A very important way to increase the settling rate of fine particles in the open ocean is via:

fecal pellets

The study of the structure of the sea floor and how the sea floor has changed through time is an example of ________ oceanography.

geological

What types of deposits do turbidity currents leave in deep sea fans?

graded bedding that begins as coarse material and becomes finer upward

In general, polar neritic sediment tends to have more ________.

gravel than in tropical waters

A tablemount is another name for a(n) ________.

guyot

A cometary model of the formation of Earth's ocean must include the chemical difference between the ________ in comet ice and that in Earth's water.

hydrogen

What sediment type(s) is/are included in the pink category labeled "Other" on the map?

hydrogenous sediments cosmogenous sediments

A tentative, testable statement about the general nature of a phenomenon is called a(n) ________.

hypothesis

The direction of motion along a seafloor transform fault is:

in the same direction as the plates are spreading.

Based on the Theory of Plate Tectonics, you would expect to find ________ heat flow at the mid-ocean ridge and ________ heat flow at subduction zones when compared to other parts of the crust.

increased; decreased

Moving from an oceanic ridge to an oceanic trench, the thickness of the lithosphere:

increases in proportion to the distance.

How often do turbidity currents occur?

infrequently

According to the fossil record on Earth, the earliest-known life-forms were primitive ________.

bacteria

The mid-ocean ridge is entirely volcanic and is composed of ________ lavas characteristic of the oceanic crust.

basaltic

The measurement of ocean depth and the charting of sea-floor topography is called __________.

bathymetry

Graded bedding provides evidence that __________.

large, heavy particles settle out first as current velocity decreases

Climate distribution on Earth is primarily controlled by:

latitude

Sediments found on continental margins are called:

neritic

The type of marine sediment that forms the thickest deposits worldwide is:

neritic, lithogenous sediment deposits.

Which type of faulting is associated with the development of new ocean floor?

normal faulting

________ are events and phenomena that we can detect with our senses.

observations

Which geologic features are associated with convergent boundaries?

ocean trenches and volcanoes

New lithosphere is produced in association with:

oceanic ridges.

Segments of the oceanic ridge system that are gentler and less rugged in slope due to faster rates of seafloor spreading are called:

oceanic rises.

The most likely place for the basic building blocks for the development of life to interact and produce life is in Earth's ________.

oceans

What did the surface of Earth look like 600 million years ago?

one large continent surrounded by ocean

Abyssal plains are large, flat features that cover about ________ of the planet.

one-third

Stanley Miller's famous experiment demonstrated that __________.

organic molecules could be produced from the mixture of gases comprising Earth's early atmosphere

The instrument that emits a high-frequency sound beam to measure the depth of the ocean developed in the 1950s is the ________.

precision-depth recorder (PDR)

When was the Precambrian eon?

prior to 600 million years ago

Plate tectonics and evolution, which are held with a high degree of confidence because of rigorous testing and verification, are examples of:

theories.

Where do coral reefs exist with sea mounts?

tropical latitudes

Which of the following is characteristic of continental-continental convergent plate boundaries?

uplifted mountain ranges

Greeks

used the polar North Star to determine latitude (distance from the equator).

Seamounts and abyssal hills are ________ in origin.

volcanic

Nearly all oceanic islands are __________. (Choose the best answer.)

volcanic in origin

Captain James Cook

was an English navigator who determined the outline of the Pacific Ocean and was the first person known to cross the Antarctic Circle.

Christopher Columbus

was an Italian navigator who made a total of four trips across the Atlantic. He was erroneously credited with discovering North America.

What factor primarily controls the distribution of calcareous ooze?

water depth

Current scientific knowledge indicates that the most likely origin of most of Earth's oceans was due to ________.

water vapor released from volcanic outgassing

Pacific Islanders

were some of the first navigators; they used stick charts to navigate the sea.

Arabs

were the dominant navigators of the Mediterranean Sea in the Middle Ages.

Phoenicians

were the first humans from the Western Hemisphere to develop the art of navigation.

To find the largest area of the ocean with the oldest ocean crust, you should go to the ________.

western Pacific

When do new oceans form?

when a continent is broken apart by a divergent boundary

Warm water (From 30°C to 350°C) hydrothermal vents form:

white smokers.

What mechanism(s) is/are responsible for transporting clay to deep ocean basins?

wind slow moving ocean currents

Where do most divergent boundaries originate?

within continents

Tectonic plates move about as fast as ________.

your fingernails grow

The largest reef system in the world is the Great Barrier Reef. Where is it located?

Australia

What is the difference between a barrier reef and an atoll?

Barrier reefs surround an inactive volcano emerging above sea level, while atolls surround the previous location of a submerged volcano.

Which type of marine sediments include siliceous and calcareous oozes?

Biogenous

Which type of sediment deposit has an average rate of deposition (per 1000 years) of 1 centimeter (0.4 inch)?

Biogenous ooze, pelagic deposit

Consider an interdisciplinary study that is aimed at understanding how ocean currents affect the distribution of coral larvae. What two disciplines of oceanography would the researchers be focused on?

Biological and physical oceanography

Who of the following is thought to be the first Viking to have seen what is now called Newfoundland?

Bjarni Herjolfsson

What kind of hydrothermal vent has the highest temperature and mineral content?

Black Smoker

Characteristics of passive continental margins include which of the following?

Broad continental shelves

When looking at the world ocean totals combined, which is the most dominant sediment worldwide?

Calcareous ooze

Trilobites were dominant during which geologic period?

Cambrian

What is the motion of a juvenile stage of the Wilson cycle?

Divergence

Which of the following was used during early exploration of the oceans to collect sediment samples?

Dredge

During the ___ phase, the atmosphere was composed of mostly water vapor (steam), small amounts of carbon dioxide, hydrogen, and other gases.

Early

Which of the following features is related to transform faults along mid-ocean ridges?

Fracture zone

Which is the correct order of coral reef development near seamounts?

Fringing reef, barrier reef, atoll

The main energy resources associated with marine sediments are petroleum and ________.

Gas Hydrates

Which of the following is a hollow steel tube with a heavy weight on top that is to collect sediment samples?

Gravity corer

Where are the only two places in the world where continental ice sheets occur today?

Greenland and Antarctica

The first systematic bathymetric measurement of the oceans were made in 1872 about the ________.

HMS Challenger

The explorer who advanced oceanography by introducing systematic soundings, or depth measurements, was __________.

James Cook

What does JOIDES stand for?

Joint Oceanographic Institutions for Deep Earth Sampling

Who left Spain in September 1519 and became the first person to complete a circumnavigation of the globe when he returned to Spain three years later?

Juan Sebastian del Caño

Volcanic ash is considered to be which type of marine sediment?

Lithogenous

Which of the following is Earth's rigid layer that includes the crust plus the topmost portion of the mantle?

Lithosphere

Which of the following represents Earth's plates that are involved in plate tectonic motion?

Lithosphere

Which type of sediment deposit has an average rate of deposition (per 1000 years) of 0.001 millimeter (0.00004 inch)?

Manganese nodule, pelagic deposit

Which of the following is the deepest trench?

Mariana

Which institution is not associated with JOIDES?

National Ocean and Atmospheric Administration

What does NOAA stand for?

National Oceanic and Atmospheric Administration

The mechanism by which populations evolve and new species develop is called:

Natural Selection

The Kuiper Belt is located beyond the orbit of which planet?

Neptune

Which part of the ocean is considered to be the most climatically sensitive regions on Earth?

North Atlantic

What are the major steps involved in the process of science?

Observation, hypothesis, testing, and theory

Most large earthquakes occur along which of the following?

Ocean trenches

What type of plate boundary will result in the formation of a volcanic island chain or arc near a deep-sea trench?

Oceanic-oceanic convergent boundaries

In which period did the first fishes appear?

Ordovician

Which layer of the Earth is composed of a liquid?

Outer Core

Which of the following was not abundant in the early atmosphere?

Oxygen

The majority of ocean trenches are along the margins of which ocean?

Pacific

Which is the largest tectonic plate?

Pacific

Deep-ocean trenches and volcanic arcs result from the collision of two plates at convergent plate boundaries and mostly occur along the margins of which of the following oceans?

Pacific Ocean

Tamu Massif, the largest single volcano on Earth occurs in which of the following oceans?

Pacific Ocean

The largest of the ocean basins, which currently covers more than half of the ocean surface, is the:

Pacific Ocean.

The San Andreas Fault in California cuts through which two plates?

Pacific Plate and North American Plate

Evidence suggests that the Sun and the rest of the solar system formed about five ________ years ago.

billion

Marine sediments that originate in the warm tropical surface ocean would create deposits in the deep sea composed primarily of ___________.

calcium carbonate

One of the reasons that free oxygen in our atmosphere is important to the development and maintenance of life on Earth is because oxygen:

can form ozone and block some UV radiation.

Which of the following was not used as evidence for continental drift?

Paleomagnetic reversals

The __________ is characterized by the extinction of 90% of marine life.

Paleozoic/Mesozoic

What was the name for the supercontinent about 200 million years ago?

Pangaea

What happens during radioactive decay?

Parent isotopes turn into daughter isotopes.

Which of the following resources found in ocean sediments has the greatest economic value?

Petroleum

Of the following, which energy resource(s) can be extracted from marine sediments?

Petroleum Gas Hydrates

The first recorded circumnavigation of Africa was made by the ________.

Phoenicians

During the _____________, the first organisms with shells developed

Precambrian/Proterozoic

During the ___ phase, the atmosphere was composed of increased amounts of atmospheric oxygen, which caused the ozone concentration in the stratosphere to increase.

Present

The speed of sound in seawater varies with ________.

Pressure, Temperature, and Salinity

Which of the following was true about the Protoearth?

Protoearth's deep structure was homogeneous.

The sea floor provides the largest reservoir of usable energy in the ocean, and likely the world, in the form of ______________.

clathrates

Which sediment type dominates in the neritic environment?

coarse lithogenous sediment, such as sand and small rocks

Of the metals commonly found in manganese nodules, ________ is the only metal deemed "strategic" for the United States.

cobalt

The method of determining latitude in the Northern Hemisphere by measuring the angle between an observer's line of site to the North Star and line of site to the northern horizon was developed by:

Pytheas.

Which of the following sediments are biogenous?

Radiolarian, diatom, & calcareous ooze

Which of the following is the major environmental concern regarding the release of methane from the sea floor to the atmosphere?

Release of large quantities of methane from the ocean causes dramatic effects on global climate.

In the ship's name, what does R/V stand for?

Research Vessel

Identify the major feature of a slow-spreading mid-ocean ridge.

Rift Valley

Sediment samples from deep beneath the ocean floor are recovered by __________.

Rotary Drilling

Which of the following is the most advanced technology used to collect sediment samples from the deep ocean?

Rotary corer

Which type of sampling did the JOIDES Resolution conduct?

Rotary drilling

Prior to 1768, which of the following claimed the most human lives at sea?

Scurvy

Why do coral reefs at the ocean surface grow away from seamounts over time?

Seamounts subside as tectonic plates move. Coral reefs grow away from the seamount in order to stay near the sunlight.

What is the difference between an ocean and a sea?

Seas are smaller and shallower bodies of salt water that are somewhat enclosed by land, but they are directly connected to the world ocean.

Which of the following techniques used to determine ocean bathymetry is illustrated in the image?

Seismic Reflection

The largest unexplored potential for metallic minerals in offshore sand deposits may exist along the west coast of ________.

South America

Which of the following is responsible for generating Earth's magnetic field?

Spinning of the metal cores

What did Stanley Miller's experiment demonstrate?

Stanley Miller's experiment demonstrated that vast amounts of simple organic molecules could have been produced in Earth's early oceans (a "prebiotic soup").

Ocean sediments consist of particles that have slowly settled out of the water by which of the following the processes?

Suspension settling

Based on definition, it is more appropriate to consider which ocean as a sea?

The Arctic Ocean

What would happen to Earth if ocean floor were created at divergent boundaries at a faster rate than it is destroyed at convergent boundaries?

The Earth would increase in volume.

Which of the following statements comparing ocean to land is correct?

The Pacific Ocean covers more of Earth's surface than all the land combined.

Which ocean is actually a part of three other oceans?

The Southern Ocean

*Which of the following statements about the average depths of the four principle oceans is correct?

The average depths of the Pacific, Atlantic, and Indian Oceans are very similar, while the depth of the Arctic Ocean is much shallower than the other three.

What is the relationship between the crust and lithosphere?

The crust is part of the lithosphere.

Collecting adequate samples from which of the following is the most difficult?

The deep-ocean floor

Which hypothesis best explains the continuous bend in the Hawaiian Islands-Emperor Seamount chain?

The direction of plate motion shifted over time over a stationary mantle plume (hotspot).

How do turbidity currents affect canyons?

Turbidity currents erode material from canyons as currents move downslope.

Most of the explorations by northern and western Europeans during the Middle (Dark) Ages were undertaken by:

Vikings of Scandinavia

What is Scurvy?

Vitamin C deficiency

In science, which one of the following would be considered an observation? Select only one answer.

Waves approach the beach at an angle

The separation of the Earth into layers while it was molten was the result of the:

differing densities of the elements that make up the Earth.

What is a volcanic arc?

a row of volcanoes that forms on the overriding plate near a subduction zone

What was Pangea?

a supercontinent that formed 300 million years ago

The Mid-Atlantic Ridge is an example of a:

divergent plate boundary.

Plates move apart at __________ boundaries, move together at __________ boundaries, and move side-by-side at __________ boundaries.

divergent/convergent/transform

Evidence shows that periodic reversals of Earth's magnetic field have resulted in __________.

a symmetrical pattern of normal and reverse magnetization in ocean crustal rocks along ridges and rises.

The average slope of the continental shelf is approximately ________.

a tenth of a degree

Volcanic features on the ocean floor that are less than 1,000 meters (0.6 miles) tall are called:

abyssal hills or seaknolls.

Radioactive materials can sometimes be used to determine the:

ages of rocks.

The nebular hypothesis suggests that ________.

all bodies in the solar system formed from an enormous gas cloud

Where is the youngest ocean floor found?

along the crest of mid-ocean ridges

Which of the following is characteristic of oceanic-continental convergent plate boundaries?

andesitic volcanoes

What factor primarily determines the distribution of radiolarian ooze?

areas of upwelling

Which layer of the Earth behaves in a plastic manner?

Asthenosphere

When did the Appalachian Mountains of North America begin to form?

450 million years ago

Which of the following ideas support our current scientific understanding of the development of life on Earth?

-Early organisms evolved into more complex organisms over time -Primitive life likely existed without the need for oxygen -The "prebiotic soup" of the primitive oceans provided favorable conditions for life to develop. -As life evolved it significantly changed Earth's environment.

Which of the following contributed to the salinity of the ocean?

-The creation of acid rain from volcanic outgassing -Chlorine gas from the atmosphere was dissolved in water -Runoff caused dissolved elements to enter the ocean

A container holds 100 atoms of an isotope. This isotope has a half-life of 1.5 months. How many total atoms will be in the container after 3 months?

100 atoms

Oxygen comprises about ________ percent of the Earth's present atmosphere.

20

A container holds 100 atoms of an isotope. This isotope has a half-life of 1.5 months. How many atoms of the radioactive isotope will be in the container after 3 months?

25 atoms

Based on chemical composition, Earth consists of ________ layers

3

The average depth of the world's oceans is approximately ________.

3,682 meters (12,080 feet)

Based on physical properties, Earth consists of ________ layers

5

The flipping of Earth's magnetic field takes an average of about ________ years.

5,000

When did the great mountain ranges of southern Europe and Asia begin to form?

50 million years ago

A ship's fathometer (an echo sounder) transmits a sound pulse and records the return of an echo 7.4 seconds later. If the speed of sound in water is 1500 m/second, what is the water depth in meters?

5550 meters

The distance of 1 fathom was standardized to equal exactly ________ feet.

6

The oceans cover approximately ________ percent of the Earth's surface.

70

What percent of volcanic activity takes place on the sea floor?

85

How many volcanic peaks are known to exist on the Pacific sea floor?

> 20,000

Which of the following is the deepest part of the ocean?

Abyssal plain

What is a tablemount?

A seamount that grew above sea level, experienced wave erosion, and is now inactive.

Which of the following is the most dominant sediment in the deepest ocean basin - the North Pacific?

Abyssal Clay

Choose the statement that offers the best explanation for the differences in sediment abundance between the North Atlantic and North Pacific basins.

Abyssal clays are more abundant in the North Pacific than the North Atlantic because calcareous oozes dissolve before reaching the sea floor in the North Atlantic ocean basin.

An organism's response to environmental changes are called ________.

Adaptations

Which of the following statements about the Pacific Ocean is TRUE?

All of the continents could fit into the space occupied by the Pacific Ocean.

What is a seamount?

An active volcano that occurs along the crest of the mid-ocean ridge.

The great oxidation event resulted in the massive die-off of which of the following?

Anaerobic bacteria

Which of the following mountain ranges are examples of continental arcs?

Andes and Cascades

*Rank the four principle oceans from smallest to largest, in terms of size.

Arctic, Indian, Atlantic, Pacific

A major characteristic of a seamount is that it is ________.

Cone shaped

What part of the continent(s) create the best fit when trying to piece them back together like a puzzle into the supercontinent Pangaea?

Continental margin

Passive margins are usually produced over geologic time by which of the following?

Continental rifting and continued sea floor spreading

Where does the deep-ocean basin begin along a passive continental margin?

Continental slope

Which of the following is the main reason that Earth has a magnetic field? Select only one answer.

Convection in the liquid iron-nickel outer core generates a magnetic field.

What is the motion of a declining stage of the Wilson cycle?

Convergence (subduction)

The Himalayan Mountains and Alps are geographic examples of which type of plate boundary?

Convergent

Which type of marine sediments include space dust and meteors?

Cosmogenous

All of the following are oceanographic sampling activities that are completed on board the ship, EXCEPT:

DNA analysis of marine organisms

The Pacific Ocean is an example of the ________ stage of the Wilson Cycle.

Declining

Active continental margins are characterized by which of the following?

Deep Sea Trenches

Shortly after the devastating 2011 Tohoku-Oki Earthquake, the Chikyu drillship began an expedition to study which of the following?

Earthquake-generated heat from friction

Which of the following is an example of the embryonic stage of the Wilson Cycle?

East Africa

Who is credited with being the first person to accurately determine Earth's circumference?

Eratosthenes

Which of the following is an example of a nematath?

Hawaiian Islands-Emperor Seamount Chain

Why are ocean basins continually being destroyed and created, rather than simply being redistributed around Earth's surface like continents?

High-density oceanic crust subducts beneath low-density continental crust where plates converge.

Which gas is being emitted from hydrothermal vents?

Hydrogen sulfide

During the ____ phase, the atmosphere was composed of leftover gases from the nebula

Initial

Which one of the following is not considered a true type of oceanic island?

Islands that are parts of continents (such as British Isles)

How did the view of the ocean by early Mediterranean cultures influence the naming of planet Earth?

Mediterranean cultures believed Earth was composed of large land masses surrounded by marginal bodies of water.

Which of the following fossils was used as data to help reconstruct Pangea because it was a reptile found in South America and Africa?

Mesosauras

The ___________ period marks the extinction of dinosaurs and many other species.

Mesozoic/Cenozoic

The ancient remains of which of the following, buried before they could decompose, are the source of today's petroleum deposits?

Microscopic organisms

In the ocean, where are the youngest rocks found?

Mid-ocean ridges

What piece of evidence supports Wegener's hypothesis of continental drift?

Modern-day species that evolved in isolation share a common ancestor.

Which of the following is not a sea?

The Yellow Sea

How can a dip needle be used to determine one's location on Earth?

The angle of magnetic field lines changes depending on where you are on Earth's surface. They are more perpendicular to Earth's surface at the poles and more parallel at the equator.

How do the physical properties of the asthenosphere differ from the lithosphere?

The athenosphere is plastic or malleable and capable of slow flow. The lithosphere is a brittle and rigid solid region comprised mostly of basalt and granite.

How are the materials that make up Earth's interior stratified in relation to their densities?

The highest-density materials are concentrated at Earth's core, whereas lower-density materials are located closer to Earth's surface.

Which of the following statements is true regarding the layer(s) of Earth that is/are responsible for the magnetic field?

The inner core is solid and the outer core is liquid, and they are both composed mainly of iron and nickel.

Which of the following statements is true of the lithosphere?

The lithosphere is composed of the crust and the uppermost portion of the mantle.

What was the one line of evidence that Alfred Wegner could not explain with continental drift?

The mechanism for the movement of the plates

Alfred Wegener's continental drift hypothesis received much hostile criticism and ridicule from the scientific community because of which of the following?

The mechanism he proposed for the movement of the continents.

Which of the following is the most convincing piece of evidence set forth to support the concept of sea floor spreading?

The oceanic pattern of alternating reversals of Earth's magnetic field

Two containers hold the same radioactive isotope. Container A contains 1000 atoms, and container B contains 500 atoms. Which of the following statements about containers A and B is true?

The rate of decay of atoms (half-life) in container B is the same as the rate of decay of atoms (half-life) in container A.

Which statement best describes the origin of Earth's oceans?

The water that fills our oceans was mostly derived from outgassing, with a minor component coming from ice comets.

What do all plate boundaries have in common? Select only one answer.

They are all associated with zones of earthquakes.

How do Earth's magnetic field lines of force currently behave?

They create loops from the center of the Earth that exit in the south and enter in the north.

What did the continents that formed during the break-up of the supercontinent 600 million years ago look like?

They were nothing like the continent shapes we see on Earth today.

Which of the following would best describe the principal goal of science? Select only one answer.

To explain the causes and effects of observable natural phenomena

According to the geological time scale, which selection lists the correct order of coexistence, from earliest to latest?

Trilobites and amphibians, insects and dinosaurs, dinosaurs and birds, flowering plants and fishes, humans and reptiles

The Red Sea is an example of ________ plate boundary.

a continental-continental divergent

Directly seaward of the continental shelf is a more steeply sloping region called the:

continental slope.

Which of the following statements about coral reefs and seamounts is most accurate?

coral reefs grow away from seamounts over time

Plate convergence begins during which stage of the Wilson Cycle?

declining

What causes melting of material under divergent plate boundaries?

decompression of rock

What are turbidity currents?

dense mixtures of sand, mud, and other debris that move at high speeds down submarine canyons

Tectonic plates are pieces of the ________ that float on the more fluid ________ below.

lithosphere; asthenosphere

Which sphere of the Earth protects life on Earth from solar storms?

magnetosphere

Where are most modern divergent plate boundaries found?

mid-ocean ridges

Which geologic features are associated with divergent boundaries?

mid-ocean ridges and continental rift valleys

Complete this statement: Divergence is to moving away as convergence is to _______.

moving toward

The study of how the ocean, atmosphere, and land have interacted in the past to produce changes in ocean chemistry, circulation, biology, and climate is called ________.

paleoceanography

The study of historical changes of continental shapes and positions is called:

paleogeography.

The oldest fossilized remains of organisms are primitive ________ bacteria recovered from rocks formed on the sea floor about 3.5 billion years ago.

photosynthetic

The study of the transmission of light and sound in the oceans is an example of ________ oceanography.

physical

Fossils of ancient tropical plants are currently found near the poles because the:

plants lived in the tropics, but landmasses have drifted to current locations.

Most large ocean floor features owe their origins to _________.

plate tectonic processes

Which process causes the surface geography of Earth to change over time?

plate tectonics

Vikings

possessed excellent ships and good navigation skills to actively explore the Atlantic Ocean in the late 10th century.

What would you look for as evidence that a rock layer formed from materials deposited by ancient turbidity currents?

repeated sequences of graded bedding that begin as coarse material and become finer upward

Neritic sediments are most likely to be composed of __________.

sand, silt, and gravel

Measurement of ocean floor bathymetry from satellites relies on ___________. Select only one answer.

sea surface elevation, which varies depending on the shape of the underlying sea floor

By analyzing cores of sediment collected from the sea floor, scientists can infer past environmental conditions on all of the following except ________.

sealife populations

In comparison with other ocean basins, major sedimentary features such as continental rises and abyssal plains are relatively rare in the Pacific. The primary reason for their scarcity in the Pacific is that __________.

sediment is trapped within the trenches of the convergent plate boundaries ringing the Pacific

Spreading centers have ________ earthquakes, while trenches have ________ earthquakes.

shallow; deep

Our world ocean can be divided into four principal oceans plus an additional ocean, based on the ________ of the ocean basins and the ________ of the continents.

shape; position

Based on the map of what the world may look like in 50 million years from now, the Pacific Ocean will become ________ while the Atlantic Ocean will become ________.

smaller; larger

The method that is used most frequently to investigate sediment and rock layers of the sea floor is:

sound waves (specifically seismic reflecting profiling).

The term referring to the size and shape of sediment particles is ________.

texture

Compared to the rest of the planet, an unusually high concentration of hotspots and rifting is located on the continent of Africa. A likely explanation for this is that __________.

the African Plate is essentially stationary with respect to Earth's interior and the thick continental crust acts as a "heat blanket"

What is the scientific definition of half-life?

the amount of time over which the number of parent isotopes decreases by half

Frederick Vine and Drummond Matthews determined that new ocean floor was being produced at ocean ridges by examining:

the magnetic pattern of rocks on the seafloor.

Relatively few abyssal plains are located in the Pacific Ocean due to:

the presence of convergent active margins.