Geology Exam 3 Self-test

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Internal Layers Of Earth Today

crust lithosphere asthenosphere upper mantle lower mantle outer core inner core

In Halite (NaCl),

each Na atom is bonded to six Cl atoms and each Cl atom is bonded to six Na atoms. This arrangement results in the atomic structure of a cube

The geothermal gradient shows how

temperature increases with depth in the Earth

Earth' Internal Heat Engine

temperature gradually increases with depth at a rate known as the geothermal gradient:

Seismic waves bend outward when traveling through

the deeper mantle due to increasing velocity with depth Increasing velocity due to increasing mantle density with depth

When seismic waves (rays) encounter a boundary between materials with different properties

the energy splits into reflected and refracted (bent) waves.

Partial Melting

the process by which different minerals in rock melt at different temperatures

When the velocity of seismic waves decreases when passing from one layer into another,

the waves refract (bend) downward away from the boundary separating the layers

When the velocity of seismic waves increases when passing from one layer into another

the waves refract (bend) upward towards the boundary separating the layers

Primary (P) waves

travel through solid rock at an average velocity of ~5 km/sec P-waves can travel through: - Solids - Liquids - Gasses

Secondary (S) waves

waves travel through solid rock at about half the speed of P-waves Also called shear waves because they push material at right angles (90o ) to their path of travel Unlike P-waves,

Continental Crust:

~40 to 65 km thick - Average composition of granite - Less dense (more buoyant) than oceanic crust. THICCER

Endogenic builds land forms:

•Igneous activity •Sedimentation •Crustal deformation and uplift

Earth's Magnetic Field

Discovered by Chinese (13th century) floating a lodestone on a piece of wood - it pointed north.

Halides

Generally form ionic bonds Some precipitate from salty water (seawater)

Paleoclimatic Evidence

Glacial deposits found today in South America, Africa, India and Australia: - Some in places where the climate is now tropical Grooves in bedrock at these locations may have been carved by ancient glaciers

Categories of Rocks

Igneous Rocks (Crystallize from magma and lava) Sedimentary Rocks (Lithification of sediment; Precipitation of ions) Metamorphic Rocks ( Formed when original parent rocks undergo changes due to changing temperature and pressure conditions)

The Earth's Magnetic Field

Liquid iron in the outer core is stirred into convective motion by Earth's internal heat Circulation of the liquid iron produces electric currents These electric currents, in turn, generate the ________

The Geologic Cycle

Two systems operating at the Earthatmosphere interface: - Endogenic (internal system) builds land forms - Exogenic (external system) wears down the land forms

Alfred Wegener

- First proposed his continental drift hypothesis in 1915 - Published The Origin of Continents and Oceans PANGEA

Major processes that have contributed to Earth's internal heat

- Heat released by colliding particles during formation of Earth - Heat released during gravitational contraction of the early Earth - Heat emitted by radioactive decay of unstable isotopes within Earth - Early impact with a Mars-sized object - Heat released as iron crystallized to form the solid inner core

Compass directions define two components of magnetism:

- Inclination - Tilt of magnetization. - Declination - Horizontal swing.

Oceanic Crust:

- Ranges from 3 to 15 km thick - Consists primarily of basalt and gabbro

Two layer mantle convection

- Separate convection cells for the upper and lower mantle - Boundary between the upper and lower mantle is the 670 km transition zone

What changes in P- and S-waves occur when encountering the outer core that lead scientists to conclude that this layer is composed of liquid iron?

-waves cannot pass through the outer core while P-waves slow down significantly when passing through this layer.

Earth Was Hit With Large Mars-sized Body

4.5 B.Y. Ago Collision caused extensive heating and melting of the Earth and impactor; Moon formed from material ejected into space

Which of the following does NOT constitute evidence for continental drift?

A cooling, shrinking Earth.

A stream terrace represents...

A former flood plain occurring along the sides of a valley above the elevation of the present stream

Which of the following statements is true for minerals?

A given mineral has a specific crystal structure and chemical composition.

Which of the following statements LEAST-LIKELY applies to landscapes?

A landscape is in steady-state equilibrium and never changes with time if all the input variables remain the same

Which of the following steps is NOT consistent with the Elastic Rebound Theory for generating an earthquake?

A persistent earthquake causes the strain around the locked fault to build up (increase) even more

Which of the following statements is an example of foliation in metamorphic rocks?

Alignment of platy minerals like micas in a common direction due to direct pressure during metamorphism.

Horizontally-layered sedimentary rocks can be folded into arches called _________ and troughs known as ____________.

Anticlines/synclines

Atoms Within Minerals

Are Arranged In Orderly Crystalline Structures

Detrital (clastic) sedimentary rocks...

Are composed of particles of pre-existing rocks

Cinder cones...

Are generally small and constructed of pyroclasic material.

Weird ice-flow directions of ancient glaciers, as evidenced today on the continents of South America, Africa, India, and Australia, make sense if we..

Assemble these continents into a giant supercontinent. Question 3

With regard to the Wilson Cycle, which of the following is an example of opening of an ocean basin?

Atlantic Ocean

The Asthenosphere Lies

Below the lithosphere and crust Upper asthenosphere is a weak zone of partially- melted peridotite that slows down seismic waves

The mineral calcite belongs to which of the following mineral groups?

Carbonates

Oxides

Cations are bounded to oxygen Hematite + Magnetite

Within limestone bedrock undergoing dissolution by slightly acidic groundwater, ________ form below the water table within the zone of saturation while ___________ form above the water table within the zone of aeration.

Caves/stalactites

Seismic Studies Suggest That The Inner Core is

Composed of Solid Iron and Nickel

Hornfels are most commonly associated with ___________ metamorphism.

Contact

_________ metamorphism is directly associated with the margins of igneous intrusions?

Contact

One way by which continents grow is through addition of igneous material along _______.

Convergent plate boundaries

Where would composite volcanoes most likely form?

Convergent plate boundary

What constitutes the plates of plate tectonics?

Crust and solid upper portion of the mantle directly above the asthenosphere

The Moho is the boundary between the ________ and _________

Crust/upper mantle

Wilson Cycle: Opening of an Ocean

Crustal doming Rifting Linear Sea mature ocean

Earth's magnetic field envisioned as an

Cylinders of spiraling liquid iron in outer core behave like coil of current passing through wires of electromagnet

What type of drainage pattern is depicted in the following illustration?

Dendritic

A light-colored igneous rock with abundant quartz and potassium feldspar is probably ________ in composition.

Felsic

Native Element Minerals are composed of only one element:

Graphite (C) - Diamond (C) - Copper (Cu) - Gold (Au) - Sulfur (S)

Exploring the Subsurface: Geophysical Surveys

Gravity data Gravity model Electrical surveys Magnetic data

Which of the following pairs of minerals belong to the same mineral group?

Gypsum and anhydrite

A low-viscosity magma most likely...

Has low silica content

Which of the following statements regarding heat flow on Earth is TRUE?

Heat flow, as measured on Earth's surface, is higher along mid-ocean ridges and other volcanically active regions but lower within the interiors of stable continents.

Which of the following is NOT a silicate mineral?

Hematite

Seismic Velocities Slow Down

In Upper Asthenosphere

Marine Magnetic Anomalies

Incredible matching magnetic stripes were found extending away from both sides of oceanic mountain chains known as mid-ocean ridges Previously-formed crust of normal polarity had split apart and move in opposite directions, forming stripes on either side of the mid-ocean ridge

The Earth 4.5 Billion Years Ago

Initial magma ocean was hundreds of km deep Magma ocean cooled and crystallized from the bottom-up over millions of years to form a solid mantle capped by a primitive crust of basalt and komatiite

Earth's overall density is calculated to be 5.52 grams per cubic centimeter. However, crustal rocks only give densities around 2.9 grams per cubic centimeter. Where is the excess density?

Iron in Earth's core

LECTURE SLIDES BEGIN

LECTURE SLIDES BEGIN

Which of the following chemical sedimentary rocks will most likely contain fossils?

Limestone

Seismic Studies Suggest That The Outer Core is Composed of

Liquid Iron

Which of the following statements regarding mid-ocean ridges is FALSE?

Lithospheric plates converge along mid-ocean ridges.

Which of the following types of magma will most likely result in fluid, basaltic lava flows and mild eruptions?

Low silica and gas-poor magma

Which of the following statements regarding cooling rates of magma is TRUE?

Magma crystallizing deep in the crust cools slowly and forms large crystals.

Circulation of liquid iron in the outer core is thought to be responsible for Earth's _____________

Magnetic field

Magnetic Reversal Time Scale

Magnetic reversals in volcanic rocks on land and in oceans were isotopically dated

What is going on in the following illustration?

Magnetization of ancient rocks point to various pole positions in the past that are artifacts of continental drift and not because poles actually migrated.

A principle driving force for the movement of lithospheric plates is/are...

Mantle convection

The Upper Transition Zone

Marks The Change From Olivine To Spinel Crystal Structure

The Lower Transition Zone

Marks The Change From Spinel To Perovskite Crystal Structure

Which of the following can have the greatest angle of repose?

Moist sand

With regard to the following figure, which of the statements below is TRUE?

Most of Earth's surface is covered by water

Which of the following features exhibits the greatest relief?

Mountains

What distinguishes the native element minerals from the other mineral groups?

Native element minerals are comprised of only one element

Definition of a Mineral

Naturally occurring and therefore generally found in nature Solid within temperature range normally found at Earth's surface

Hydrothermal metamorphism will most likely occur...

Near mid-ocean ridges

Which of the following is LEAST LIKELY an environmental effect of an explosive volcanic eruption (see Fig. 1.7 in textbook)?

Net increase in solar radiation at Earth's surface

New Oceanic Lithosphere Formed At Mid-ocean Ridge Is

New Oceanic Lithosphere Formed At Mid-ocean Ridge Is

P-wave shadow zones are regions on Earth's surface where...

No P-waves are detected by seismometers.

The following figure illustrates a ____________ fault that forms due to ___________ stress.

Normal/tensional

Studies of the ocean floor indicate that oceanic crust varies in age from place to place. Which of the following statements is FALSE?

Oceanic crust becomes progressively older as we approach a mid-ocean ridge.

Which of the following is LEAST likely to be a plate boundary?

Oceanic hot spot

Which of the following statements is FALSE regarding drainage systems and basins?

Only a large area covering several states can be considered a drainage basin.

Which of the following is NOT characteristic of a craton?

Only consists of undeformed sedimentary rocks younger than 500 million years

Which of the following statements regarding the Rock Cycle is FALSE?

Only igneous rocks can be uplifted and exposed to weathering.

Which of the following statements regarding convergent plate boundaries is FALSE?

Only occurs where a continental plate meets an oceanic plate

The figure below illustrates the motion of ____________

P-waves

Seismic Waves Arrive at a Seismograph Station in Three Distinct Groups

P-waves, traveling the fastest, arrives at station first S-waves arrive at station next Surface waves are slowest and arrive last

Wegener assembled the continents like pieces of a jigsaw puzzle into a giant supercontinent called...

Pangea

How does breccia differ from conglomerate?

Particles in breccia are angular, while particles in conglomerate are rounded.

The upper mantle is composed largely of a rock called ___________

Peridotite

_________involves the mechanical breakdown of rocks into smaller particles without changing the overall composition of the minerals.

Physical weathering

Which of the following statements is TRUE?

Plate tectonics is a process by which lithospheric plates are created along mid-ocean ridges and afterwards recycled back into the mantle along subduction zones.

Transform Fault Boundaries

Plates slide laterally past one another: - Lithosphere is neither created nor destroyed Transform faults are important features in ocean basins and on continents

Which of the following statements is FALSE?

Polarity reversals in Earth's magnetic field only affect the magnetic inclination, but not the declination, of ancient rocks.

Quartz sandstone is metamorphosed into ___________.

Quartzite

To Trace Seismic Waves Through Earth's Interior

Rays Originating At The Source And Constructed Perpendicular To Wave Fronts Can Be Used

The bending of seismic waves when passing through Earth's interior is called _________

Refraction

Lithosphere (sphere of rock):

Relatively cool, rigid layer - Averages about 100 km in thickness, but may be 250 km or more thick beneath the older portions of the continents - Lithosphere broken into a series of plates

Which of the following LEAST LIKELY forms in response to compressional stress?

Rift valley

Which of the following is an erosional agent that removes weathered products from the site of weathering?

Rivers and streams Groundwater Glaciers Wind All of the above

Which of the following types of slope failure is the fastest?

Rock fall

Each of the following are reactants in the weathering process except for _______, which is a product of weathering.

Rock fragments

Origin of Magma

Role of heat: - Temperature increase in the upper crust (geothermal gradient) averages between 20oC to 30oC per kilometer depth - Rocks in the lower crust and upper mantle are near their melting points - Any additional heat may induce melting

What type of mass movement is depicted in the figure below?

Rotational slide

What happens to S-waves as they pass through the asthenosphere?

S-waves slow down because of the presence of a few percent partial melt

Which of the following is NOT a foliated metamorphic rock?

Sandstone

Determining Ages Of Oceanic Crust

Seafloor is dated using fossils from overlying sediments and correlating magnetic stripes with the Geomagnetic Time Scale: - Seafloor spreading occurs at rates ranging from 1-18 centimeters per year - Youngest oceanic crust occurs along mid-ocean ridges - Oceanic crust becomes progressively older away from ridges - Oldest oceanic crust only Late Jurassic (~180 m.y. old) in age

Which of the following statements regarding silicate minerals is false?

Silicate tetrahedra can bond with cations but not with other tetrahedra.

Major Classes of Rock-Forming Minerals

Silicates Oxides Halides Carbonates

Silicate Minerals

Silicon ion (Si4+) surrounded by four oxygen ions (O2- ) and represented by the formula (SiO4 ) 4-

What are the two dominant igneous intrusions illustrated below?

Sill and dike

For the figure below, which letter corresponds to the epicenter of the earthquake?

Site B

Which of the following most likely causes a supercontinent to break apart?

Supercontinent prevents heat in the underlying mantle from escaping, thus generating upwelling mantle plumes that break the supercontinent apart.

Seismic Waves

Tectonic forces can cause the rigid crust of the Earth to deform and break along faults Slippage along faults releases energy as seismic waves Seismic waves travel through the Earth in all directions as vibrations that we recognize as earthquakes

____________ stress and strain most likely occur along a divergent plate boundary.

Tensional

Which of the following is (are) LEAST LIKELY associated with a convergent plate boundary?

Tensional stress

Below The 670 Km Transition Zone Lies

The Mesosphere (Lower Mantle)

Which of the following statements regarding reversals in Earth's magnetic field is TRUE?

The Geomagnetic Time Scale indicates numerous reversals in Earth's magnetic field over the last 5 million years.

Plates

The lithosphere is divided into plates of different sizes The plates are separated by three types of boundaries: - Divergent (mid-ocean ridges) where plates pull apart - Convergent (subduction zones) where plates come together - Transform boundaries where plates slide laterally past one another

Carbonates

There are different carbonate minerals depending on which cation is attached to the carbonate complex: Basic unit is the (CO3 ) 2- complex

The Lower Asthenosphere Includes

Two Transition Zones Characterized By Increases In Seismic Wave Velocities

What happens to P- and S-waves when encountering transition zones at 400 km and 700 km depths?

They speed up due to density increases in mantle rock resulting from phase changes in minerals.

Seismic Tomography

Three dimensional model of Earth's interior based on seismic imaging Requires seismic records from many different earthquakes Identifies regions where P- and S-waves are faster or slower than average Velocity variations of seismic waves attributed to variable temperatures and other material properties: - Higher temperatures, slower velocities - Lower temperatures, greater velocities

Where would you least expect to find active volcanoes?

Transform plate boundary

East African (Afar) Triple Junction

Two arms open up into linear seas Third arm is a failed rift Upwarping causes lithosphere to split into three arms (branches) Upwelling mantle plume impinges on base of lithosphere

Convergent Plate Boundaries

Two plates come together with one plate (usually oceanic) subducting (sinking) beneath another along an oceanic trench

According to the Rock Cycle, which of the following is the first stage in converting a metamorphic rock into a sedimentary rock?

Uplift and exposure

Which of the following is NOT a sedimentary environment where sediments accumulate?

Uplifted bedrock undergoing weathering and erosion

Whole-mantle convection

Upper and lower mantle part of one large convection system - Hot, rising mantle plumes originate at the core-mantle boundary

Investigating Deep Processes

Use computers to model Earth's interior based on seismic refraction data

Mesosphere (Lower Mantle)

Velocities of P- and S-waves increase with depth in the (Lower Mantle) Rocks in the _________ are solid but very hot and capable of flow

The bending of seismic waves when passing through Earth's interior is due to changes in wave ____________ when encountering different Earth materials.

Velocity

Which of the following is NOT a direct product of weathering?

Water

Exogenic wears down land forms:

Weathering •Erosion •Mass wasting

Grooves in Bedrock Indicate

Weird Ice Flow Directions

Which of the following characterizes a stream that has reached base level?

Wide flood plain

Seismic Velocities Increase

With Depth Within The Lithosphere

The following figure illustrates how the root zones of ancient mountain ranges consisting of igneous and metamorphic rocks eventually reach the surface. These ancient root zones are most likely exposed today...

Within the shield areas of cratons

Tectonic Cycle

also powered by Earth's internal heat energy, brings internal heat to surface, generates new crust, moves and deforms crust, and recycles crustal material

Surface waves

are confined to the surface and outer layers of the Earth Travel at speeds slightly less than that of S-waves Similar to waves in the ocean Do most of the destruction during an earthquake

Melting temperatures of dry peridotite

are everywhere higher than geothermal gradient

Sulfides

compounds that consist of one or more elements combined with sulfur

A magma rich in dissolved gases will produce...

explosive eruptions and volcanic ash.

Paleo-Magnetic Reversals

geophysicists found that some older layers exhibited polarity opposite from Earth's present magnetic field: - Earth's magnetic field reversed in the past Evidence suggests that Earth's magnetic field flipped from normal to reverse polarity, then back again, many times in the past

Intraplate Volcanism

igneous activity that occurs within a tectonic plate away from plate boundaries

Seismographs

instruments that measure the vibrations in the ground

The Geothermal Gradient

is a curve showing the increase of temperature with depth

Long-lived radioactive isotopes

keep planet warm today

S-waves cannot travel through

liquid outer core

Sulfates

minerals that contain sulfur and oxygen

Short-lived radioactive isotopes

only had half lives of a few million years and have long since decayed

P-waves bend downward when entering the

outer core due to a decrease in velocity... Bending of P waves in the outer core creates P-wave shadow zone

Rock Cycle,

powered by Earth's internal heat energy, produces the three basic rock types found in the crust

Hydrologic Cycle,

powered by solar energy, transfers and stores water in various reservoirs

Wet peridotite partially melts at depths below ~60 km (upper mantle) to

produce basaltic magma


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