GEO105H Exam #1

What are xenoliths, of what importance are they?

"Foreign rock" - Fragments of mantle, ripped up and brought up by volcanic eruptions

How did evidence from ancient fossil, glacial deposits, and mountain belt distribution contribute to early models of geographic continental fit?

-Jigsaw puzzle fit -Fossil evidence -Climatic evidence -Glaciers -Evidence that thick glacial ice sheets once covered areas currently located in the tropics -Desert belts -Mountain Belts Line Up when continents are placed into a Pangaea configuration

How do we recognize the different layers of the Earth's interior?

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What are the P and S wave shadow zones? How Is each generated?

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What are the special properties of seismic waves as they travel thru the earth‟s interior?

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Draw a generalized cross section of an subduction zone depicting: A) the Benioff zone B) volcanic arc C) ocean crust D) ocean trench

A) B) C) Crust-crust; older subduct D)

The fastest seafloor spreading today occurs where? A) Eastern Pacific B) North Atlantic C) South Atlantic D) Indian Ocean

A) Eastern Pacific

Which of the following statements is true? A) Most of the continental crust is older than the oceanic crust. B) Most of the oceanic crust is older than the continental crust. C) Continental crust and oceanic crust are approximately the same age. D) All of the oceanic crust is older than the continental crust.

A) Most of the continental crust is older than the oceanic crust.

What is the name of the ancient ocean that surrounded Pangaea? A) Panthalassa B) Tethys C) Laurasia D) Rheic

A) Panthalassa

What is the name of the ancient ocean that surrounded Pangaea? A) Panthalassa B) Tethys C) Laurasia D) Rheic

A) Panthalassa

At approximately which time period did scientists begin to note observations such as coastline shapes that could be explained if the Americas and Europe had been part of a larger continent? A) about 1600 B) 1880 C) 1920 D) 1960

A) about 1600

The earthquakes and volcanoes of the Pacific "Ring of Fire" are associated with what type of plate boundaries? A) convergent B) divergent C) transform D) convergent and divergent

A) convergent

The Moho is a geophysical discontinuity that marks the base of the: A) crust B) mantle C) outer core D) inner core

A) crust

Which of the following features is NOT associated with a divergent plate boundary? A) deep-sea trenches B) earthquakes C) mid-ocean ridges D) continental rift

A) deep-sea trenches

Which of the following features is NOT associated with a divergent plate boundary? A) deep-sea trenches B) earthquakes C) mid-ocean ridges D) continental rift

A) deep-sea trenches

Which of the following phenomena is normally present at all types of plate boundaries? A) earthquakes B) volcanic activity C) mountain building D) formation of new crust

A) earthquakes

The curve that describes how temperature increases with depth within the Earth is called the: A) geothermal gradient. B) geoid. C) dipole. D) Earththerm.

A) geothermal gradient.

A plate bounded on all sides by divergent margins: A) must be getting smaller. B) must be getting larger. C) must remain the same size. D) Size change cannot be determined.

A) must be getting smaller.

The process by which plates separate and oceanic crust is created is called: A) seafloor spreading. B) subduction. C) continental drift. D) transform.

A) seafloor spreading.

At a transform boundary, plates _____________ one another. A) slide past B) move toward C) move apart from D) move over

A) slide past

What is a transform fault ? How/why do they form ?

Area where two pieces of lithosphere slide past one another

The oldest oceanic rocks are about___ Ma (million years ago), which records about ___ of Earth history. A) 2,000,000; 50% B) 200; 4% C) 1; 2% D) 2; 4%

B) 200; 4%

The oldest oceanic rocks are about___ million years old, which records about ___ of Earth history. A) 2,000,000; 50% B) 200; 4% C) 1; 2% D) 2; 4%

B) 200; 4%

Which of the following mountain ranges did not form as a result of continent-continent collision? A) Appalachian Mountains B) Andes Mountains C) Himalayas D) Ural Mountains

B) Andes Mountains

Eduard Seuss proposed that the present-day southern continents once formed a single giant continent that he called: A) Rodinia B) Gondwanaland C) Pangaea D) Appalachia

B) Gondwanaland

Which seismologist determined depth to Earth's core? A) Benioff B) Gutenberg C) Lehmann D) Oldham

B) Gutenberg

What is the name of the large supercontinent that existed about 225 million years ago when all the continents were together? A) Rodinia B) Pangea C) Gondwanaland D) Nazsca

B) Pangea

Which of the following statements comparing rates of plate motion determined from seafloor magnetic anomalies and the global positioning system (GPS) is correct? A) Rates of plate motions over the past decade are much faster than rates over the past several million years. B) Rates of plate motions over the past decade are very similar to rates over the past several million years. C) Rates of plate motions over the past decade are much slower than rates over the past several million years. D) Plate motion has apparently stopped, as GPS shows no motion.

B) Rates of plate motions over the past decade are very similar to rates over the past several million years.

Which of the following statements about the Earth's crust is true? A) The oceanic crust is thicker than the continental crust. B) The oceanic crust is thinner than the continental crust. C) The oceanic crust and the continental crust have the same thickness. D) Part of the oceanic crust is thicker and part is thinner than the continental crust.

B) The oceanic crust is thinner than the continental crust.

The low-velocity zone involves a decrease in ____________ velocity as partial melting of ________________ causes a decrease in rigidity. A) surface wave; peridotite B) body-wave; peridotite C) surface wave; granite D) P-wave; basalt

B) body-wave; peridotite

The breakup of the continents Antarctica and Australia was likely a major cause for what significant change in our Earth system? A) evolution of difference species of aquatic mammals B) changes in ocean current patterns influencing global climate C) increased mountain formation in North America D) None of the answers is correct.

B) changes in ocean current patterns influencing global climate

Which statement correctly relates plate boundaries to associated changes in plate area? A) convergent - area increases; divergent - area decreases; transform - area is unchanged B) convergent - area decreases; divergent - area increases; transform - area is unchanged C) convergent - area decreases; divergent - area increases; transform - area change cannot be predicted D) Plate interactions at all boundaries causes increases in plate area.

B) convergent - area decreases; divergent - area increases; transform - area is unchanged

New oceanic lithosphere forms at ____________ plate boundaries. A) convergent B) divergent C) transform D) convergent and transform

B) divergent

The Red Sea represents a ______________ plate boundary. A) transform B) divergent C) convergent D) within

B) divergent

At a hot spot, heat causes melting of a small portion of the ______________, which then erupts to Earth's surface. A) crust B) mantle C) outer core D) inner core

B) mantle

Seafloor spreading refers to: A) sediments from the continents spreading over the seafloor. B) older ocean floor moving away from a mid-ocean ridge with new seafloor forming in the resulting gap. C) the seafloor stretching thinner and thinner as continents pull away from each other. D) weight of the ocean floor pushes the ocean floor down, stretching it.

B) older ocean floor moving away from a mid-ocean ridge with new seafloor forming in the resulting gap.

Seismic tomography can detect relatively warm regions of the mantle because seismic waves: A) do not pass through these regions. B) travel more slowly through these regions. C) travel more rapidly through these regions. D) Seismic tomography doesn't use seismic waves.

B) travel more slowly through these regions.

What are the different seismic waves? What special characteristics do they have (ie. what can they travel thru, velocities, etc...).

Body waves which includes: 1) Primary waves (P-waves) - Fastest, travels by alternating compression and expansion, travels thru any material 2) Secondary waves (S-waves) - Second fastest, travels by lateral shearing, travels thru solids only Surface waves - Travels along Earth's surface

Why does the presence of fossils of the reptile mesosaurus only in South America and Africa support a previous connection between the two continents about 300 million years ago? A) Mesosaurus was a fresh water organism and could not have travelled across an ocean between continents. B) Evolution would cause the development of different species (and different fossils) for later times, consistent with observations. C) Both A and B are correct. D) Neither A nor B are correct.

C) Both A and B are correct.

Which seismologist discovered Earth's inner core? A) J. T. Wilson B) A. Wegener C) I. Lehmann D) B. Gutenberg

C) I. Lehmann

Which statement best describes the geometry and geographic distribution of the North American plate? A) Its boundary aligns with the coastline of the United States and Canada. B) It includes a small portion of submarine continental material surrounding the North American continent. C) It ranges from the Pacific Coast to the center of the Atlantic Ocean. D) Its size and geometry is an ongoing topic of scientific investigation.

C) It ranges from the Pacific Coast to the center of the Atlantic Ocean.

If there were no convergent plate boundaries, and only spreading centers at mid-ocean ridges were present on Earth, what would happen to our planet? A) Nothing - it would behave just as it does today. B) It would shrink. C) It would expand. D) Its shape would change to be increasingly flattened.

C) It would expand.

What happens when seismic waves encounter a boundary between two materials? A) All the wave energy bounces off the boundary. B) All the wave energy passes through the boundary. C) Some of the wave energy bounces off the boundary and some passes through the boundary. D) The wave energy is all absorbed at the boundary.

C) Some of the wave energy bounces off the boundary and some passes through the boundary.

Seismic P-waves are a type of: A) shear wave B) surface wave C) compressional wave D) water wave caused by wind

C) compressional wave

Earthquakes are associated with which of the following types of plate boundaries? A) divergent and convergent B) convergent and transform C) convergent, divergent, and transform D) convergent

C) convergent, divergent, and transform

Iceland sits atop which type of plate boundary? A) ocean-ocean convergent B) ocean-continent convergent C) divergent D) transform

C) divergent

Three basic types of plate boundaries: A) divergent, convergent, subduction B) divergent, mid-ocean ridge, rift C) divergent, convergent, transform D) convergent, continent-continent collision, transform

C) divergent, convergent, transform

A tectonic plate that is being subducted along much of its boundary tends to move _________ a tectonic plate that is not being sub ducted. A) slower than B) at the same rate as C) faster than D) over

C) faster than

The chain of volcanoes that forms at an ocean-ocean convergent plate boundary is referred to as a(n) ___________ arc. A) continental B) subduction C) island D) ocean

C) island

Lines on a map of the seafloor that connect rocks of the same age are called A) isograds B) isotopes C) isochrons D) isometrics

C) isochrons

Seafloor spreading occurs along: A) bands of earthquakes and volcanoes at continent boundaries. B) volcanic island chains such as the Hawaiian Islands. C) mid-ocean ridges. D) oceanic trenches.

C) mid-ocean ridges.

Plate movement is parallel to: A) subduction zones. B) spreading ridges. C) oceanic transform faults. D) None of the answers is correct.

C) oceanic transform faults.

At a continent-ocean convergent boundary, the _________ plate will subduct, because it is ______________. A) continental; more dense B) continental; hotter C) oceanic; more dense D) oceanic; hotter

C) oceanic; more dense

The S wave shadow zone is caused by the: A) inner core. B) lower mantle. C) outer core. D) upper mantle.

C) outer core.

S-waves are transmitted through: A) solid, liquid, and gas B) solid and liquid, but not gas C) solid only D) vacuum only

C) solid only

What type of plate boundary is the San Andreas fault? A) convergent B) divergent C) transform D) It is not a plate boundary.

C) transform

The asthenosphere is in the: A) crust B) lower mantle C) upper mantle D) core

C) upper mantle

The magnetic time scale is: A) a detailed history of Earth's magnetic field reversals. B) used in determining rates of plate motion. C) used in determining ages of ocean floor rock. D) All of the answers are correct.

D) All of the answers are correct.

What evidence helped give strong support for the hypothesis of seafloor spreading at mid-ocean ridges? A) frequent earthquakes located along the ridges B) a rift present along the crest of the ridges C) samples of very young basalt taken from the seafloor of the Atlantic Ocean D) All of the answers are correct.

D) All of the answers are correct.

Which of the following is not convincing evidence that South America and Africa were once joined as one continent? A) Atlantic coasts of the two continents would fit neatly together. B) 300 million-year-old fossils of identical land-dwelling animals are found on both continents. C) Evidence that glaciation occurred on southern portions of both continents at the same time. D) Both continents today have tropical rainforests in some areas and deserts in other areas.

D) Both continents today have tropical rainforests in some areas and deserts in other areas.

What was the major shortcoming of Wegener's hypothesis of continental drift? A) His only evidence was matching shapes of continents, which could have been a coincidence. B) He was trained as a meteorologist, and any research on geologic topics would have been invalid. C) He presented supporting geological observations related to ancient fossils and glacial activity, but they were incorrect. D) His mechanism for the cause for the motions of continents was shown to be impossible.

D) His mechanism for the cause for the motions of continents was shown to be impossible.

Relative velocities from fastest to slowest: A) S-wave, P-wave, surface waves B) P-wave, surface wave, S-wave C) surface wave, P-wave, S-wave D) P-wave, S-wave, surface waves

D) P-wave, S-wave, surface waves

Why does the S-wave shadow zone occur? A) S-waves don't travel through solids. B) S-waves don't travel through a vacuum. C) S-waves don't travel through a gas. D) S-waves don't travel through a liquid.

D) S-waves don't travel through a liquid.

Much of our best information about Earth's interior comes from: A) biology B) sociology C) astronomy D) seismology

D) seismology

All plates are bounded by: A) divergent boundaries. B) convergent boundaries. C) transform boundaries. D) some combination of divergent, convergent, and transform boundaries.

D) some combination of divergent, convergent, and transform boundaries.

What controls seismic wave velocity? What is seismic tomography?

DIfferent layers due to composition (i.e. Asthenosphere="plastic zone"=low velocity zone). Seismic tomography - taking temp of earth's mantle

What are 'back-arc basins"? How do they develop? What is an example?

Developed behind volcanic arcs; extension behind volcanic arc b/c mantle convecting

What is meant by dip-slip and strike-slip motion?

Dip-slip: Motion along the fault is generally vertical (up and down) Strike-slip: Motion along the faults is generally horizontal (side to side)

What are magnetic reversals?

Every ~75,000 years or so the earth's magnetic field reverses/flips

How did magnetic reversals prove sea-floor spreading (plate tectonics)?

Every ~75,000 years or so the earth's magnetic field reverses/flips "flips" are recorded in the rock record Magmas coming out of the surface often contain magnetite Magnetic->aligns with magnetic field like a compass Perfectly symmetrical pattern from magnetite's alternating pattern - seafloor stripes

What are ophiolites? How do they form? What rocks that make up an ophiolite in sequence?

Fragments of ocean floor that have been pushed on top of the continental crust

What is a hanging wall? A footwall?

Hanging wall - Hang lamps Footfall - Walk on floor

What are accreted terranes?

Islands or fragments of continents that gets stuck to the leading edge of a continent as it moves Ex.: Hawaii slamming into Japan

What is a hot spot? How do the size/age of the Hawaiian Islands relate to hot spots ?

Isolated areas of volcanism not associated with any plate boundary; Columns of magma from the d' layer (fed from the deep mantle) rising up and generating volcanoes Lithosphere moves->mantle plume shifted->current volcano extinct, new volcanoes form (example: Hawai'i)

Contrast the lithosphere and asthenosphere.

Lithosphere - Crust and upper mantle Asthenosphere - "Plastic zone" within the upper mantle

What is the Moho (Mohorhovcic) Discontinuity, Lehman Discontinuity, Gutenberg Discontinuity?

Moho - Boundary between crust and mantle Lehman - Boundary between mantle and outer core Gutenberg - Boundary between outer core and inner core

Discuss the 3 different forms of convergent boundaries.

Ocean-Ocean Ocean-Continent Continent-Continent - Causes ocean basin to disappear, Change ocean circulation, Cause glacial period Creates high mountains

Contrast the nature of oceanic and continental crust in terms of: A) rock types B) crust thickness C) age D) density

Oceanic: A) Basalt B) Thin C) Young D) Less dense Continental: A) Granitic material B) Relatively thick C) Old D) More dense

Be able to predict plate motions based on tectonic sketches.

Okay

Where is Earth's magnetic field generated and how?

Outer core; liquid outer core causes convention->rotation generates magnetic field

What was Pangea? Gondwanaland? Laurasia?

Pangea - all present land masses were joined together as a supercontinent Gondwanaland - Southern Hemisphere Laurasia - Northern Hemisphere

What is the "geothermal gradient"?

Rate of increasing temperature with respect to increasing depth in the Earth's interior (25C/km depth)

What is paleomagnetism? How does it relate to the concept of seafloor spreading?

Study of Earth's ancient magnetic field, every ~75,000 years or so the earth's magnetic field reverses/flips, Magmas coming out of the surface often contain magnetite; Once these rocks cool below their "Curie temperature" (~750C), the rocks permanently record the position of the magnetic field

What is the "Wilson Cycle"? What does it represent?

The moving apart and closing off cycle of the mid-ocean ridge

Why was continental drift not accepted until after World War II?

Wegener's mechanism for the cause for the motions of continents was shown to be impossible

What are triple junctions? Where do they form and why?

When lithosphere first breaks from pushing mantle plume, it breaks into a "Y"-shaped pattern, forms from hot spots

What are "large igneous provinces"? What do they represent?

When mantle plumes first reach surface they generate huge volcanic eruptions

What is the "elastic rebound theory of earthquakes"?

accumulation and release of stress and strain

What is the "Curie Temperature"?

~750C

On what basis did Wegener propose the existence of a supercontinent?

• Jigsaw puzzle fit • Fossil evidence • Climatic evidence • Glaciers • Desert belts