Deck 5: The Tectonic Cycle

Question 1

Using the concepts of hot spots and plate tectonics, explain how each of the islands of the Hawaiian Island chain vary in age.

Answer 1

The Hawaiian Island chain is a result of the movement of the Pacific Plate over a hot spot in the Earth's mantle. A hot spot is an area of intense volcanic activity caused by a plume of hot magma rising from deep within the Earth. As the Pacific Plate moves northwestward over the hot spot, it creates a series of volcanic islands.

The oldest island in the Hawaiian chain is Kauai, which formed over 5 million years ago. As the Pacific Plate continued to move, new volcanic activity formed the islands of Oahu, Molokai, Lanai, Maui, and finally the Big Island of Hawaii, which is still actively growing due to ongoing volcanic eruptions.

The varying ages of the Hawaiian Islands can be attributed to the movement of the Pacific Plate over the hot spot. As the plate moves, older islands become more distant from the hot spot and undergo erosion, while new islands continue to form near the hot spot. This process results in a chain of islands that vary in age, with the oldest islands in the northwest and the youngest islands in the southeast. This demonstrates the dynamic nature of plate tectonics and the formation of volcanic islands.

Question 2

Discuss the evidence to support plate tectonics. In your discussion, include what lead to Alfred Wegener's Continental Drift Hypothesis, and what additional evidence is used today to support plate tectonics.

Answer 2

The evidence supporting plate tectonics is vast and compelling, with key pieces of evidence dating back to the early 20th century when Alfred Wegener proposed his Continental Drift Hypothesis. Wegener suggested that the continents were once joined together in a single landmass he called Pangaea, which over millions of years, broke apart and drifted to their current positions.

Wegener's hypothesis was based on several lines of evidence, including the jigsaw-like fit of the continents, similarities in rock types and mountain ranges across different continents, and the distribution of fossil species that were once thought to be unable to travel across vast oceans. However, Wegener's ideas were met with skepticism at the time due to the lack of a mechanism to explain how the continents could move.

Today, the evidence supporting plate tectonics includes the mapping of mid-ocean ridges and deep-sea trenches, the discovery of magnetic striping on the ocean floor that indicated seafloor spreading, and the identification of tectonic plate boundaries where earthquakes and volcanic activity are concentrated. Additionally, the study of paleomagnetism has provided further evidence, as the orientation of magnetic minerals in rocks can be used to track the movement of tectonic plates over time.

Furthermore, advancements in technology, such as GPS and satellite imagery, have allowed scientists to directly measure the movement of tectonic plates and monitor changes in the Earth's crust. This wealth of evidence has solidified our understanding of plate tectonics and its role in shaping the Earth's surface, from the formation of mountain ranges to the occurrence of earthquakes and volcanic eruptions. Overall, the evidence for plate tectonics is robust and continues to be supported by ongoing research and observations.

Question 3

__________ has emerged as a unifying theory that explains hundreds of years of independent observations of Earth's topographic features.

Answer 3

Plate tectonics

Question 4

It was __________ who realized that the Andes Mountains were slowly being pushed upward.

Question 5

__________ suggested __________ , in which all of the world's landmasses were once connected together in a huge supercontinent called __________ .

Question 6

__________ is the preservation of Earth's magnetic field locked in minerals at the time of rock formation.

Question 7

Earth is like a giant magnet, surrounded by an invisible __________ that permeates everything placed in the field.

Question 8

Through detailed paleomagnetic studies, scientists have been able to determine a chronology of __________ reversals of Earth's magnetic field.

Question 9

The principle mechanism by which heat is transferred from deep inside Earth to the base of the lithosphere is __________ .

Question 10

__________ plate margins are fractures in the lithosphere where two plates move apart.

Question 11

__________ plate margins occur where two plates are moving toward each other.

Question 12

___________ plate margins are fractures in the lithosphere where two plates slide past each other.

Question 13

Large, flat areas known as __________ are a major topographic feature of the seafloor.

Question 14

An __________ marks the place where oceanic-capped lithosphere sinks into the asthenosphere.

Question 15

The Atlantic Ocean margins of the Americas, Africa, and Europe are examples of __________ continental margins.

Question 16

A __________ is a stable core of very ancient rock.

Question 17

The lithosphere behaves as is it were __________ on the asthenosphere.

Question 18

__________ gravity anomalies result from concentrations of high-density rock under the surface.

Question 19

Gases from __________ continue to play an important role in the climate and the long-term composition of the atmosphere.

Question 20

__________ has influenced virtually every part of the Earth system over the history of planet Earth.

Question 21

Continental Drift is a unifying theory that explains Earth's topography and integrates our understanding of rock formation, mountain building, and terrain modification.

Question 22

Studies of rock paleomagnetism have revealed the ancient positions of Earth's magnetic poles.

Question 23

In seafloor convergence, oceanic crust splits and moves away from spreading ridges.

Question 24

The driving force for lithospheric plate motion is conduction in the mantle.

Question 25

Measuring the speed and direction of movement of lithospheric plates requires a fixed frame of reference, such as distant stars.

Question 26

Earth's diameter is increasing significantly due to the generation of new ocean crust.

Question 27

Since Pangaea, the lithosphere has broken into nine major plates and a large number of smaller plates.

Question 28

Divergent plate margins start in continents and become oceans.

Question 29

When two plates capped by dense oceanic crust converge, one of the plates will subduct beneath the other plate.

Question 30

When a plate capped by continental crust converges with a plate capped by oceanic crust, the continental plate will undergo subduction.

Question 31

When both plates of a converging pair are capped by low-density continental crust, neither plate will undergo subduction.

Question 32

As the plates of a transform fault grind past one another their edges may grab and lock, forcing the rocks on both sides to flex and bend.

Question 33

Modern continental shorelines coincide exactly with the edges of the original oceanic rift.

Question 34

Subduction zones are marked by deep trenches where ocean-capped lithosphere sinks into the asthenosphere.

Question 35

Passive continental margins coincide with the geologically active edges of tectonic plates.

Question 36

Oceanic crust is geologically old and preserves a long record of geologic activity.

Question 37

If plate tectonics operated early in Earth history, it is likely that the plates were small, rapidly moving, and constantly recycled back into the mantle.

Question 38

Cratons are isostatically instable.

Question 39

Large mountain ranges are characterized by significant negative gravity anomalies because of their deep, low-density roots.

Question 40

Earth's climatic zones and the distribution of plant and animal communities are fundamentally affected by the presence of modern orogens.

Question 41

Where is active sea-floor spreading occurring today?

A) Lake Michigan
B) The Great Salt Lake.
C) The Red Sea.
D) The Mississippi River.

Question 42

What is a subduction zone?

A) Where a continental plate breaks and diverges.
B) Where one lithospheric plate is dragged or pushed below another lithospheric plate.
C) Where one lithospheric plate slides past another lithospheric plate.
D) None of the above

Question 43

What type of plate boundary created the Himalaya Mountains?

A) Transform.
B) Divergent.
C) Convergent.

Question 44

What type of plate boundary created Japan?

A) Convergent.
B) Divergent.
C) Transform.

Question 45

What type of plate boundary created Iceland?

A) Convergent.
B) Divergent.
C) Transform.

Question 46

What type of plate boundary created the Andes Mountains?

A) Convergent.
B) Divergent.
C) Transform.

Question 47

What type of plate boundary is associated with the San Andreas Fault in California?

A) Divergent.
B) Convergent.
C) Transform.

Question 48

How do hot spots and plate tectonics account for the islands of the Hawaiian Island chain varying in age?

A) The volcanic hot spot in the middle of the Pacific Ocean was originally in the Atlantic Ocean and is therefore quite old.
B) Hot spots and plate tectonics cannot account for the age variability.
C) The volcanic hot spot in the middle of the Pacific Ocean is due to the divergence of the East Pacific Rise.
D) As molten material continually seeped from the hot spot, an island(s) would form. As the Pacific Plate continued to move the island locked to the Pacific Plate would move as well. A new island would then form above the hot spot.

Question 49

The Earth's oldest rocks are found

A) In the abyssal plains.
B) On volcanic islands like Hawaii.
C) In the cores of continents.
D) At the mid-ocean ridges.

Question 50

The mesosaurus is an extinct reptile who lived over 200 million years ago. Its fossil remains have been found in Southern Africa and Eastern South America, but nowhere else. Today, we know that these two regions of the Earth are vastly different in terms of climatology, flora, and fauna. How does the discovery of the mesosaurus fossil support the concept of Continental Drift (and subsequently Plate Tectonics)?

A) Mesosaurus was a coastal animal and therefore could not have crossed the Atlantic Ocean. The distribution of the mesosaurus fossils indicate that the two continents used to be joined together.
B) It really doesn't. The mesosaurus was a good swimmer and most likely swam the expanse of the Atlantic Ocean.
C) The distribution of the mesosaurus indicates that the fauna of Southern Africa and Eastern South America used to be the same, but nothing else.

Question 51

Why are the continents about 20 times older than the oldest ocean basins?

A) Because ocean basins form from spreading centers, which produces new oceanic crust.
B) Because continental material is low-density and does not get thrust into the subduction zone.
C) Both of these are true

Question 52

What was the first evidence that lead Alfred Wegener to suspect the continents were once connected?

A) The clock-like ebb and flow of the tides.
B) The continents simply looked like they fit together, especially Africa and South America.
C) The direction that the currents moved.
D) Alfred Wegener discovered marine sediments in the Himalaya Mountains.

Question 53

What type of plate margin is the majority of the rim surrounding the Pacific Ocean?

A) Active.
B) Passive.

Question 54

If indeed there are reversals of the Earth's magnetic field, how can we prove this within the context of plate tectonics?

A) The magnetic field reversals have led to subduction zones.
B) The magnetic field reversals have led to sea-floor spreading.
C) We see magnetic directional patterns in the magnetite of ocean-floor rocks symmetric to mid-ocean ridges.
D) The magnetic field reversals have led to the creation of mountains (like the Andes).

Question 55

Apparent polar wandering is best explained by

A) Magnetic reversals.
B) The movement of Earth's axis of rotation.
C) The movements of the continents.
D) In truth, the magnetic poles wander significantly.

Question 56

Subduction zones can generally lead to

A) Deep trenches.
B) Island arcs.
C) Mountain ranges.
D) Any of these.

Question 57

Of the following, which can be used to determine the absolute motion of plates?

A) Volcanic hot spots (such as the Hawaiian Island chain).
B) Magnetic reversals chronicled in the oceanic crust.
C) Sediment thickness along continental margins.
D) The position of Australia relative to the other continents.

Question 58

Along what type of plate boundary does subduction occur?

A) Divergent.
B) Convergent.
C) Transform.

Question 59

Along what type of plate boundary does sea-floor spreading occur?

A) Convergent.
B) Divergent.
C) Transform.

Question 60

The Continental Drift hypothesis was rejected by the scientific community primarily because Alfred Wegener did not

A) Offer observational evidence to support continental drift.
B) Identify a mechanism that would lead to the movement of the continents.
C) Know much about geology.
D) All of the above.

Question 61

Which of the following is not evidence supporting plate tectonics?

A) Paleoclimatology.
B) Magnetic reversals.
C) Apparent polar wandering.
D) Changes in lunar tides.

Question 62

The highest temperature at which magnetic material can retain permanent magnetization is called the

A) Newton Point..
B) Curie Point
C) Centigrade Scale.
D) Fahrenheit Proximity.

Question 63

A typical rate of seafloor spreading along the Mid-Atlantic Ridge is

A) 2 to 4 cm/year.
B) 2 to 4 feet/year.
C) 2 to 4 inches/year.
D) 2 to 4 meters/year.

Question 64

Which of the following statements is true for the asthenosphere?

A) The material that makes up the Himalaya Mountains.
B) A brittle layer of crust plus upper mantle.
C) The origination point for Earth's internal convection of energy.
D) Zone in the upper mantle that is a solid but capable of flowing like a liquid.

Question 65

How does plate tectonics influence the composition of ocean water?

A) Submarine volcanoes along mid-ocean ridges lead to chemical reactions between the ocean water and the hot rocks of the seafloor.
B) Material from the core seeps into the ocean via submarine volcanoes.
C) Oceanic trenches from subduction zones trap salts and minerals thereby changing the overall ocean water composition.
D) None of these.

Question 66

What does the flotation height of an object depend upon?

A) Mass and volume.
B) Mass and density.
C) Volume and density.
D) Size and shape.

Question 67

Although the Himalaya Mountains are still growing today, eventually (regardless of whether the collision between the Australian-Indian plate and the Eurasian plate continues or not) the mountain will stop growing. Why is that?

A) Meteorite impacts.
B) Gravitational anomalies.
C) Isostatic adjustment.
D) Solar radiation eroding the top of the mountain.

Question 68

An assemblage of cratons and orogens is called a

A) Continent.
B) Continental shield.
C) Ocean basin.
D) Subduction zone.

Question 69

The break-up of Pangaea to form our modern-day continents started about how long ago?

A) 100 million years ago.
B) 200 million years ago.
C) 300 million years ago.
D) 50 million years ago.

Question 70

Assume there is a mountain range with a deep root of low-density continental rock extending into the underlying asthenosphere. Would this produce a negative or positive gravity anomaly?

A) Positive.
B) Negative.
C) Need more information to answer this question.

Question 71

About how old is the oldest craton within the North American continental shield?

A) Greater than 2.5 billion years old.
B) About 2 billion years old.
C) About 1 billion years old.
D) Less than 1 billion years old.

Question 72

About how old are the oldest known rocks on Earth?

A) 4.56 billion years old.
B) 2.98 billion years old.
C) 3.51 billion years old.
D) 2.57 billion years old.
E) 4.28 billion years old.

Question 73

The volcanic mountain range of the Andes is defined as a

A) Volcanic island arc.
B) Continental volcanic arc.
C) Himalaya-like mountain zone.
D) Mini-supercontinent.

Question 74

What is the Benioff Zone?

A) The contact zone where one slab of lithosphere subducts beneath another slab of lithosphere.
B) The contact zone where one slab of lithosphere diverges from another slab of lithosphere.
C) The contact zone where one slab of lithosphere moves adjacent to another slab of lithosphere.
D) The oceanic zone where hydrothermal vents exist.