Geology Exam 1

The earth, other planets, and the sun all formed at about the same time. Evidence (primarily from meteorites and lunar samples) suggests that this was ________ years ago.

4,500 million

How is a tsunami wave generated? And, in the open ocean, at what sort of speeds do tsunami waves travel?

A tsunami wave can be generated by powerful volcanic eruptions that are right below sea level, big underwater landslides or landslides originating from coastal mountains that crash into the ocean below, the impact of meteorites, and of course, powerful earthquakes that shake the ocean floor (usually happening at or near subduction zones). In the ocean, tsunamis can move up to hundreds of kilometers per hour (usually upwards of 800 kilometers per hour).

What sort of basic dip-slip fault types would you expect to be associated with-- 1st, A) Rifting Events (e.g. mid-ocean ridges, or continental pull-apart zones) ? 2nd, B) Mountain Building events (e.g. continental collision) ?

A) Normal and detachment faults. B)Reverse and thrust faults.

BUT, there is another important reason that we cannot just use rocks (that were never alive) for C-dating. WHY is that?

Another reason carbon dating does not work well on rocks is because carbon dating mandates that the materials being tested have interacted with the atmosphere using photosynthesis or respiration. Rocks are not alive, and therefore do not use either of those processes. Usually, carbon dating is done on bone, wood, or other carbonate materials. However, carbon dating CAN be used on very young sediments. Key Idea=> the organism had to interact with atmospheric carbon,, where C-14 is -continually re-generated (upper atmosphere)!

What kind of igneous rock is produced at a spreading ridge—basalt, or rhyolite, or andesite?

Basalt Yes. Hi percentage melting of asthenospheric mantle makes basalt.A mid ocean ridge is a place where the deeper mantle (i.e. the asthenosphere) is rising.Why is there melting beneath a mid-ocean ridge?-- due to reducing of pressure on the "plastic-like" mantle as it rises. Called "Decompression" melting.

The Mohorovicic Discontinuity (Moho) separates the

Mantle/Crust

Canadian Shield (quiz answer)

a region of exposed cratonic rocks.

The western margin of north america is a(n) _____________plate margin, whereas the eastern margin of the African continent is a(n)______________plate margin. Group of answer choices

active, passive

A scientific theory is

among other things, well substantiated and has been thoroughly tested.

Nonconformity

an igneous or metamorphic rock, formed, was uplifted and eroded, and then had sedimentary layers deposited atop.

The Appalachians are a good example of

an old mountain range

Faunal succession is most helpful in recognizing a kind of unconformity in which sedimentary layers are undistrubed (i.e. flat lying) like in a layer cake. In this kind of unconformity (with flat-lying layers) there is a large time gap between the layers. This kind of unconformity is called a(n) ________.

disconformities.

Probably the biggest problem with Wegener's theory of continental drift was that

his mechanism was not consistent with what geologists understood about the strength of rocks.

Elastic rebound theory can be described as a model for

how rocks eventually break (rupture) when sufficient stress is applied.

Faunal succession

is the recognition of that different kinds of life lived at different times in the past.

The age of ocean floor rocks are generally

less than 200 million years.

The tremendous thermal energy generated inside the earth through the decay of radioactive elements eventually finds its way to the surface (via conduction and convection). This energy is the main driving force behind all the following phenomena except

movement of water in the hydrologic cycle (rivers, glaciers, etc.) (other answers were: volcanic eruptions movements of tectonic plates earthquakes)

Transform boundaries occur where--

oceanic lithosphere slides laterally past continental lithosphere oceanic lithosphere slides laterally past oceanic lithosphere continental lithosphere slides laterally past continental lithosphere

You are standing in the middle of a road on the west side of a strike slip fault looking eastward across the fault. The road has been displaced southward on the opposite side of the fault. You are looking at a ______ fault that is ______ the San Andreas fault.

right lateral, like

Paraconformity

a disconformity that is not well represented by an wavy erosion surface.

Which of the following rates represents a geologically typical plate motion velocity?.001 cm per year, 5 cm per year, or 100 cm per year----> Pick ONE

5 cm per year Sure, typical plate velocities are anywhere from 1-15 (or so) centimeters per year

Really, a subduction zone is a fault-- with motion of rock along a surface. Question: What sort of fault is this? (thrust/reverse, or strike-slip, or normal?) Explain.

A subduction zone is a thrust fault. Thrust faults form in parts of the crust that are being compressed, and subduction zones involve compression. Sometimes, subduction zones are even referred to as "megathrust faults".

Some mountain ranges, notably the Sierra Nevada and (to some extent) the Rocky Mountains LACK substantial crustal roots. Question...WHY IS THIS?

Although most tall mountain ranges have deep crustal roots, the Sierra Nevadas and the Rockies are a bit of an anomaly. Seismic testing of the lithospheric mantle suggests that the lithosphere underneath the Sierra Nevadas and Rocky mountains is lower density/buoyant which holds up the crust. Some sources also point to the fact that the mantle underneath the Rockies is unusually warm, which expands the mantle, and that expansion pushes up the crust, which in turn lifts up the Rocky Mountains.

What is the difference between an earthquake "epicenter" and an earthquake "focus"?

An earthquake focus is the initial point where rocks rupture in the crust. An earthquake epicenter is the point on the surface of the land that is directly above the focus. Sure, it's the difference between "point of rupture" within the earth (focus) and the point on the earth's surface directly ABOVE the point of rupture (epicenter).

Approximately when did Pangea BEGIN its initial break-up?

Answers for this question seem to be slightly varied across sources, but the consensus is that Pangea started the process of breaking up approximately 250 million - 180 million years ago. AND... this is precisely why the oldest ocean crust is only about 180-190 my old.Was there ocean crust before this? Almost undoubtedly so, but it was all subducted away, prior to the accretion of Pangaea.

At the end of this video, it's mentioned that geologists will sometimes recommend drilling into a particular kind of fold, in order to hit trapped oil. Is this fold an ANTICLINE or a SYNCLINE?--- select one of those fold types!

Anticline anticlines are "dome-shaped" upwarps (like upside down bowls!),, and if a layer is impermeable to oil,, then oil tends to migrate upwards and collect beneath this roof-like-layer!

what are the various dangers associated with caldera forming eruptions?

Ash Fall, Pyroclastic Ash Flows (PF's), Lahars, and certain noxious/poisonous gas emissions. Not to mention longer term dangers that could include detrimental changes to climate, water, and to soils in the region.

Recognizing that this proximity of the newly formed ocean crust to the subduction trench means that the descending plate was relatively warm....decide whether or not the subduction angle at that time would have been steep or shallow. Please explain your reasoning.

Because the descending plate was relatively warm, I assume that the subduction angle would have been more on the shallow side, as the plate is not very dense. Older and colder plates tend to be more dense, and therefore have steeper subduction angles. key idea:"Near the ridge" means that the ocean crust is relatively WARM (compared to ocean crust further from a ridge)... WARM rock is more buoyant (i.e. less dense) and therefore--- we expect a SHALLOW subduction angle

How Do We Know where the MOHO is located, or that it even exists??

By measuring seismic waves, we are able to figure out what type of material is inside earth and its location. The rate in which the seismic waves are traveling suggests what kind of material the waves are traveling through. Mohorovicic found that at a certain depth, the P- and S-waves change in speed, which led him to believe there was some sort of boundary between the crust and the mantle. The Moho was discovered in the early 1900's.It was determined that seismic waves with travel paths that were relatively deep in the earth (below about 15km oceans and about 30km continents) went zipping along quite quickly. This "fast zone" turned out to be the upper mantle!In other words—he found that there were two generally DIFFERENT seismic wave speeds,, depending on how deep the waves were traveling!

Which is a correct comparison of oceanic and continental crust?

Continental crust is thicker, lower density, and higher in silica (i.e. "felsic") compared to oceanic crust.

True or False: Anticlines always form topographic ridge-like features.

False

Understanding the origin and composition of earth's core region requires...

Fe-Ni meteorite analysis seismic wave analysis theoretical modeling

OUTER CORE --> mostly solid, or mostly liquid (i.e. fully molten), or partially molten (i.e. significant portions of melt, but not fully molten) ??

Fully molten

How does the boiling temperature of water change with pressure? In other words, does high pressure result in a higher or lower boiling point?

High pressure results in a higher boiling point. Due to high pressure, water under a geyser becomes superheated or above the normal boiling point. When the superheated water rises, the pressure and boiling point drops, which allows the water to turn into steam and blast out of the geyser.

Define what we mean by "INDEX FOSSILS" and explain how they are used in determining sedimentary rock ages. (In other words-- what are the characteristics of good index fossil?)

Index fossils are remains of species that were geographically wide-spread, abundant, easy to identify/distinctive, and represent a short-lived period of existence. The location/specific sedimentary rock the index fossils are found in can help determine the age of said sedimentary rock if we know when that certain species was alive. Yes, a good index (or "guide") fossil is wide-ranging and has a short geologic time span as a species. With guide/ fossils, a "long-lived" species is LESS useful because it cannot pin point a particular moment in geologic time.

Once it detached from Pangaea, did the Indian subcontinent moved relatively rapidly-- Did it move NORTHWARD OR SOUTHWARD?

India broke away at around 110 million years ago and moved rapidly northward. Yes, northward motion,And, compared to other plate motion (typically about 1-10cm/yr), India was moving along more "rapidly"!

The video shows a feature known as "stream capture". What is meant by that term?

It means that as the strike slip fault moves along, erosion happens, and the rivers on either side of the fault start to flow and funnel its water into new channels. The constant horizontal movement of the fault means that the rivers are constantly changing and flowing into one another, as if they are "stealing" or "capturing" water from each other. Stream Capture= when a stream channel is caught up (captured/intercepted) by another stream channel

Fold and thrust belts are characterized by

Large overthrust faults, crustal shortening, and crustal thickening

What magnitude earthquakes are typical of mid-ocean ridge; high (6 or greater) or low (5 or less).

Low magnitude earthquakes are typical of mid-ocean ridges. The deepest and most powerful earthquakes tend to be those originating from subduction zones this is probably a consequence of the relatively "warm" crust is present at MORs(mid-oceanridges).... This warm rock has a tendency to deform in a more plastic (than brittle) manner. This means that there is less chance to build up stress for large earthquakes.

CRUST --> mostly solid, or mostly liquid (i.e. fully molten), or partially molten (i.e. significant portions of melt, but not fully molten) ??

Mostly solid

INNER CORE --> mostly solid, or mostly liquid (i.e. fully molten), or partially molten (i.e. significant portions of melt, but not fully molten) ??

Mostly solid

LITHOSPHERE --> mostly solid, or mostly liquid (i.e. fully molten), or partially molten (i.e. significant portions of melt, but not fully molten) ??

Mostly solid

Craton (textbook answer)

Much of the old crust, or "basement rock" as it is sometimes called, can be covered by younger sediments. So the colored map here of North American Age Provinces refers to the deep roots of the continent. These roots are called the continental CRATON and where it is exposed (with no overlying sediment of younger age) it is called a SHIELD region.

Why are the magnetic lineations identical on either side of the mid-ocean ridge?

New ocean crust is moving laterally and uniformly away from the ridge in TWO equal/opposite directions---new crust is produced and moves perpendicularly away from the ridge. As the crust cools, it acquires the prevailing magnetic field. So, since the magma comes out on BOTH sides and moves outwards in BOTH directions, and acquires the prevailing magnetic field orientation....they are more or less identical on either side of the ridge. Upwelling new lava, right along the ridge crest, moves outwards, on either side, like a conveyor belt. Each side is cooling and receiving the same magnetic "imprint" from the earth's prevailing magnetic field. —therefore, you get a kind of mirror image effect, where both sides show the same magnetic anomaly pattern.

Which type of unconformity (angular, nonconformity, or disconformity) involves original crystalline rock (formed at high temperature=>igneous or metamorphic) which has been uplifted and eroded AND THEN covered by subsequent sedimentary layers?

Nonconformity.

The first seismic waves to arrive at a seismic station are

P waves.

HOW DOES the P-wave seismic velocity of the lower mantle compare to the P-wave seismic velocity of the outer core?

Pwave velocity in lower mantle is GREATER than that in the outer core. See figure-- Pwave velocity shows a huge drop, going from lower mantle to outer core And, the trend in the mantle itself is that velocity INCREASES with depth.But things change dramatically as the waves enter the outer core (where they slow). The slow-down (upon entering the outer core) is probably because the outer core is a liquid (and liquids don't transport pwaves at very high velocities)

Explain why rocks sometimes FOLD instead of fault. And, as part of the explanation, discuss what geologic conditions would favor folding (bending) versus faulting (breaking)?

Rocks can fold instead of fault when they are in a more "plastic" state. Folds occur when there are certain combinations of composition, temperature (typically higher), strain rate, and lithostatic pressure. Rocks are more likely to undergo folding deeper within the earth with constant pressure and temperature rather than closer to the surface, where they are more likely to break and be less plastic. Folding requires compressive stress (=directed pressure) AND elevated temperature. Elevated temperatures are a necessity in order to make rocks ductile as opposed to brittle!

Which separated from Pangaea first, North America or South America

The North American plate separated from Pangaea first, about 180 million years ago. The South American plate pulled away later, around 120 million years ago. Yes, and this is why the North Atlantic is broader than the South Atlantic (it's been spreading for a longer period of time).

What do we call the application of FORCE that produces a change in shape within a rock? A) Strain, B) Stress

Stress "change in shape" of a rock is STRAIN and it is caused by the FORCES that we call "stress."

What sort of fault is the San Andreas?--- A. Normal Fault B. Reverse Fault C. Strike Slip LEFT LATERAL (transform) Fault D. Strike Slip RIGHT LATERAL (transform) Fault

Strike Slip right lateral (transform) fault

Which of the following fault types does NOT tend to move rocks in a vertical sense (i.e does not move rocks on either side of the fault up or down relative to other side)?? A) Strike-Slip, B) normal, C) thrust

Strike slip

Ophiolites provide a means to examine ancient

oceanic lithosphere

The asthenosphere is mostly... (solid, liquid, partially molten)?

The asthenosphere is also mostly solid, but does have portions of melt (in other words, it is "near" it's melt point).... If you consider the INNER core, it's interesting because it is a place that is insanely hot (like similar to surface of sun! 6000 degrees or so) but it is SOLID,, and that's because super high pressure prevents melting!

If you simply ground up a detrital sedimentary rock, and obtained an isotopic date, would that date most likely be younger or older than the TRUE age of the sedimentary rock?

The date would most likely be older than the true age of the sedimentary rock itself because sedimentary rock is composed of much older rocks. With isotopic dating alone, there is no way to really tell when the sedimentary rock itself was formed/cemented together. Since sedimentary rock generally forms at lower temperatures, the rock fragments/minerals usually keep their original ages. We can only speculate how old specific rock fragments/grains in the sedimentary rock are, but we cannot obtain a definitive dating on when the sedimentary rock itself was formed using isotopic dating. Bingo!by FAR, the BIGGEST problem with using isotopic dating for detrital sed rocks is that these kinds of rocks are composed of fragments of pre-existing rock. (i.e. "detrital" sedimentary rocks).

How does the "magnetic dip angle" vary with latitude? (HINT: Think about where on the earth the magnetic field lines are vertical and where they are horizontal, relative to earth's surface.)

The magnetic field lines at both North and South poles are vertical relative to Earth's surface. If you hold a compass in the Northern Hemisphere for instance, the North end of the needle will point downwards. If holding a compass in the Southern Hemisphere, the North end of the needle will point upwards. At high latitude (i.e. polar regions) = steep dip (near 90degrees)At low latitude (i.e. equatorial regions) = shallow dip (near 0 degrees, i.e. parallel to earth's surface).

A tectonic boundary where one tectonic plate is subducted beneath another is a

convergent boundary

How does the amount (i.e. volume of magma per year) of igneous rock production at the world's mid-ocean spreading ridges compare to the amount of magma produced by land volcanoes— much more at mid-ocean ridges, or much less at mid-ocean ridges? Pick one of the above AND EXPLAIN YOUR ANSWER.

The volume of magma produced per year is greater at the mid-ocean ridges. This is because the magma at mid-ocean ridges is constantly flowing and the new basalt is constantly pushed outwards by the divergent plate boundary. By contrast, land volcanoes mostly erupt occasionally and magma is not necessarily flowing constantly. Yes, upwards of ¾ (or more) of all volcanic rock produced on earth, per year, comes out at spreading centers (=mid ocean ridges)

In a black smoker environment, where does the water come from that we see flowing out of the "chimney" structure— Is the water coming from the surrounding seawater, or is the water coming up from earth's mantle? (Pick one AND EXPLAIN YOUR ANSWER.)

The water that comes out of the chimney structure is seawater that seeps through fractures and pores in the oceanic crust. The water is heated and then escapes from hydrothermal vents.

Canadian Shield (textbook answer)

We'd expect that early continents had new continental fragments added on with time. This is exactly what we see in North America (and on many other continents)- the oldest continental crust is in the north part of the continent, in what we call the Canadian Shield region. In the adjoining diagram, the Canadian Shield is composed of very old rock (purple and pink), in excess of 2.3 billion years. Around this "proto-continent" we find younger and younger crust, e.g. the green and yellow and blue material, younger than 1 billion years.

What sort of rocks would you expect to find in the center of an eroded SYNCLINE (or basin-type down-warp)-- Young rocks or Old rocks?

Young rocks. In a syncline, the youngest layer of rock is at the fold's center or hinge. Center of a SYNCLINE== Younger rocks.Why?--- because the young rocks (which before folding, sit on top) have been wrapped down and around the central core of old rocks as a consequence of compression.(Older rocks are found in the core/center of an anticline.)

One of the following is NOT a typical feature of a passive continental margin-which is it?

a deep trench (other answers were: continental shelf, slope and rise limited volcanic activity limited earthquake activity)

angular unconformity

a series of sedimentary rock has been tilted and then eroded (the dark line is the erosion surface) and then had sedimentary layers deposited atop.

Disconformity

a series of sedimentary rock has two layers that have a lengthy separation in time, marked by the lower layer having undergone a lengthy period of erosion (indicated by the wavy dark line). Then sedimentary layers were deposited atop.

The lithosphere is all of the following except

a zone that includes deep parts of the mantle. Other answers were (a zone that includes the continental and oceanic crust, a zone of rigid rock, a zone above the asthenosphere.)

Polar wandering refers to the ________ movement of the ancient magnetic poles, at the time a particular rock forms and retains the prevailing magnetic field.

apparent (but not actual)

The Sierra Nevada in California, the Tetons in Wyoming and the Basin and Range Province in Nevada are all examples of a(n)

block-fault mountain area

S-waves

cannot pass through liquids

Divisions of time on a geologic time chart are fundamentally based on Group of answer choices

changes in fossil assemblages

A lithospheric plate includes

crust upper-most mantle

An object that returns to its original shape after the force is released is ______ and an object that continuously deforms under force is ______.

elastic, plastic

True or false: A magnitude 6 earthquake is twice as powerful as a magnitude 3 earthquake.

false

Oceanic lithosphere is composed of the following rocks

gabbro. pillow basalts. pelagic sediment. ultramafic rocks. (it is NOT composed of andesite)

Evidence for "turbidity currents" has included

graded bedding on the continental rise. submarine telegraph cable breaks. shallow water fossils in abyssal sediments. (there have been NO eyewitness accounts)

What is the primary force that generates "ridge push"??

gravity

Which of the following is not used to determine relative time.

half-life (other options are: superposition, cross-cutting relationships, lateral continuity)

A plunging fold (syncline or anticline) is one that Group of answer choices

has a dipping (i.e. non-horizontal) "fold axis"

As a tsunami wave approaches shore-like all waves-its _________.

height (i.e. "wave amplitude") increases

Isotopic (sometimes called "radiometric") dates are best determined using Group of answer choices

igneous rocks.

The deepest portions of earth's oceans are found

in subduction zone trenches

At an ocean-continent Benioff Zone (where subduction occurs), the earthquake depth ______ as one moves further from the trench, and towards the continent interior.

increases

Earth's core is primarily made of

iron and nickel

Early evidence for continental drift (e.g. Alfred Wegener's work) included

matching of continental outlines. very similar rocks and fossils on separate continents. continuous climatic zones on a reassembled Pangea.

Which of the following is a correct match of fault type and stress?

normal, extension reverse, compression

Magnetic reversals

occur irregularly, but on average, about every 500,000yrs

An anticline is a fold in which the Group of answer choices

the limbs dip away from the axis and it is a upward arching fold.

Craton (quiz answer)

those portions of a continent composed of ancient Precambrian bedrock.

Unconformities refer to missing

time.