Geology Exam 3 Self-test
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
