Geology 101 Final Exam

Which of the following statements about deep (slab) earthquakes is NOT true?

Deep (slab) earthquakes have higher maximum intensities than a crustal quake of comparable magnitude

What are the differences between relative and absolute age?

Relative age is determined by stratigraphic principles and places rock layers/geologic events in chronological order, while absolute age determines numerical dates via the radioactive decay rate.

Which of the following is not a feature of divergent plate boundaries?

Reverse faults

The best way to distinguish halite from calcite is by their different

cleavage directions

Mt. St. Helens is an example of a

composite volcano

Which of the following is NOT a characteristic of divergent plate boundaries?

composite volcanoes

The most silica rich magma compositions are found in

continental arcs

Place the following stages of deformation in order of least stress required to most stress required:

elastic, ductile, fracture

Monoclines form as a result of

fault movement in underlying rock

Most deaths due to the Laki eruption in Iceland were a result of

fluoride poisoning

A geologic structure produced by ductile deformation is called a

fold

An index mineral of high grade metamorphism is

garnet

An igneous rock with a felsic composition and a coarse texture would be called

granite

the time required for 1/2 of atoms of particular radioisotopes to decay

half-life

On what basis are Mercalli intensity values assigned to locations?

qualitative perceptions of and damage caused by the earthquake

Which of the following minerals undergoes mostly physical weathering with little or no chemical weathering?

quartz

when unstable isotopes lose mass from the nucleus in order to become more stable

radioactive decay

In Oregon west of the Cascades we would expect to find ________ faults, while east of the Cascades _________ faults predominate.

reverse or thrust; normal

What type of fault is the San Andreas Fault?

right lateral strike-slip

How would you identify the presence of an syncline by looking at a geologic map?

rock layers would dip toward each other, with the youngest layer in the middle

Original horizontality

sediments deposited in horizontal layers - deformation occurs later

Consider the minerals that make up the following rocks. Which rock will be most likely to show ductile behavior?

shale

Calcium carbonate sediments such as limestones are deposited in

shallow, tropical oceans

The study of the age of rock layers and the environments they represent is

stratigraphy

Galena is a(n) _______ mineral and the primary source of _________.

sulphide, lead

The strike of a tilted rock layer is

the compass direction of its intersection with a horizontal surface

Richter magnitude underestimates the true size of very large earthquakes because

the largest earthquakes rupture very long segments of faults

At convergent plate boundaries,

the plate of higher density subducts into the mantle

Which segment of the San Andreas Fault in northern/central California has the highest risk of producing an earthquake in the next several decades?

the segment between San Francisco and San Jose

oxidation of organic matter by respiration

aerobic metabolism

An example of an oxide mineral is

hematite

A mafic magma is a magma that is

high in silica and high in sodium and potassium

The presence of ripples or cross-bedding indicates sediment deposited by

running water or wind

High grade metamorphism of shale produces

schist

How do seismic waves change when passing through soft sediments, such as those that underlie the Willamette Valley?

velocity decreases and amplitiude increases

Seismic S waves produce

vertical motion perpendicular to the direction of wave propagation

Typical rates of plate movement are

2 to 3 centimeters per year.

4. How are absolute ages of rocks determined?

Absolute age is determined by looking at the level of radioactive decay in the rock if the decay's half-life is known, in which case the ratio of parent to daughter atoms can be used to distinguish how much time has passed since the rock was formed.

Which statement best describes our understanding of when to expect the next large Cascadia subduction zone earthquake?

Although the average time between CSZ earthquakes is 500 years, radiocarbon dating of drowned coastal forests and tsunami sand layers in coastal marshes shows that the time between CSZ earthquakes has varied from 150 to 1000 years. Because it has been 300 years since the last CSZ earthquake, the next CSZ earthquake could occur today or not for another 700 years.

11. Outline the evolution of the different vertebrate groups. Include the evolutionary advances made by each group.

Amphibians - evolved from fish, the earliest vertebrates, by the end of Devonian Period. Flourished in the Mississippian and Pennsylvanian Periods due to the abundance of suitable habitat at the time. They are tied to water as a means of reproduction, since their eggs are soft and the young breathe with gills. Reptiles - evolved during the Permian Period when vast deserts had formed on the Pangaea, replacing amphibians as the dominant land vertebrates. They lay hard-shelled eggs which may be laid on land and are more closely related to mammals than to dinosaurs, despite appearances. Archosaurs - overtook mammal-like reptiles during the Triassic Takeover as they evolved a superior limb structure, with legs underneath the body rather than at the sides. Archosaurs included dinosaurs, marine reptiles, and flying reptiles, after evolving from feathered dinosaurs of the Jurassic Period. Mammals - evolved to be endothermic (having the ability to regulate body temperature), have insulating hair, and give birth to live young. They were generalists until the extinction of dinosaurs at the end of the Cretaceous Period, and it is hard to separate the fossils of "true" mammals from those of mammal-like reptiles since mammalian traits are not observable in fossils.

Using the elastic rebound theory, describe what happens to the rocks at the focus before, during, and after an earthquake.

As described by the elastic rebound theory, rigid rocks at the focus of the earthquake break once their elastic strain limit is reached, allowing brittle behavior to dominate. After this, the elastic strain is recovered replaced by displacement along the fault, starting the process over again.

Which of the following list of igneous rocks are all extrusive?

Basalt, rhyolite, andesite

What properties determine whether a rock deforms by ductile deformation or brittle deformation? Include an explanation of the conditions that favor brittle deformation, and those that favor ductile deformation.

Brittle vs ductile behavior is determined by pressure, temperature, strain rate, and composition. Low pressure and temperature favors brittle behavior, while high pressure and temperature favors ductile behavior, as well as low strain rate. Rocks made of certain minerals also tend to be more brittle (basalt, granite, etc) or more ductile (shale, limestone, etc). It is more common to see brittle behavior near the surface, while ductile behavior is more common with increasing depth.

What are the types and tectonic settings of metamorphism?

Burial - basins, passive margins Subduction - accretion at subduction zones Regional - collisional mountain belts Contact - volcanic arcs

Describe the identification and naming of the different types of sedimentary rocks.

Clastic - composed of insoluble weathering products (solid mineral grains), and classified by their particle size. Chemical - composed of soluble weathering products (dissolved ions), classified by composition. Biogenic - composed of organic remains (plant matter, shells, etc), classified by composition.

The _____________________ are being formed by accretion of buoyant materials onto the overriding plate, while the _________________ are being formed by magma intrusion and volcanism above the depth where the subducting plate is causing melting in the upper mantle.

Coastal ranges, Cascades

Which of the following rocks was formed in the fastest-moving water?

Conglomerate

recognize strata in different areas as equivalent in age

Correlation

igneous intrusions or faults younger than rocks they intrude or offset

Cross-cutting

7. What was Earth's first atmosphere like and how did it form?

Earth's first atmosphere was similar to those of Venus and Mars and formed from the degassing of Earth's interior following accretion and differentiation. It was composed of carbon dioxide, methane, ammonia, and water vapor, as well as sulfur, nitrogen, and halogens. The volcanoes of today still release the same gases.

3. What are unconformities, and how does each type of unconformity form?

Gaps in stratigraphic record which represent missing time, or rock not formed/lost to erosion. The three types are: • Nonconformity - sedimentary rocks directly over igneous intrusion or metamorphic rocks • Angular unconformity - horizontal layers over tilted layers • Disconformity - erosional surface between horizontal layers

fragments of old rock incorporated in younger rock

Inclusions

The rocks of the core consist mostly of:

Iron and nickel

A relatively new technology that has been very effective in identifying and mapping faults in areas with heavy weathering and thick vegetation (such as western Oregon) is

LiDAR

6. Why did life evolve on Earth, and how did life most likely start?

Life evolved on earth due to a combination of the distance from the sun (not too hot or cold), being of a good size (enough gravity to hold atmosphere, but not enough to result in a thick atmosphere of solar gasses; large enough to still have a hot interior and active tectonics), plate tectonics which recycle earth materials such as CO2, and a magnetic field which protects the surface from cosmic radiation. The oxygenated atmosphere of present was not necessary for life to begin and came later, in the Proterozoic Eon. The most likely hypothesis for the start of life is that life started at hydrothermal vents on the sea floor, which would have provided energy from sulfur and protection from ultraviolet radiation. This hypothesis is supported by evidence from a genetic analysis of archaebacteria (the oldest life forms on earth and the closest living link to ancestors of all life) found in hot springs.

Subjecting ____________ to metamorphism turns it into marble.

Limestone

13. What are mass extinctions? What may have caused the mass extinction at the end of the Cretaceous?

Mass extinctions are events in which entire groups of plants or animals die out, marking the end of periods and eras since those are grouped by fossil similarity. The mass extinction at the end of the Cretaceous Period was caused by the impact of a massive asteroid.

Describe the sense of movement and types of stresses associated with normal, reverse, and strike-slip faults.

Normal faults feature vertical down-dip motion. Reverse faults feature vertical up-dip motion. Strike-slip faults feature horizontal motion parallel to the strike, which can be left or right lateral. Types of stress responsible for each type of fault? compression (reverse), tension (normal), shear (strike-slip)

Which of these minerals has the greatest hardness?

Olivine

12. List the periods of the Paleozoic, Mesozoic, and Cenozoic Era, and describe the geologic events, environments, and animals that characterized each era.

Paleozoic - • Early and middle: Cambrian, Ordovician, Silurian, Devonian • 541 - 359 million years ago • Earth composed of shallow seas in tropical latitudes; marine sedimentary rocks were common and there was ideal habitat for the diversification of marine invertebrates; rich fossil records of these • Supercontinent near the north pole (South America, Africa, India, Australia, Antarctica, Madagascar) • Occasionally glaciated during early period, leading to changes in sea level and mass extinction of marine invertebrates • Subduction zone forms on the east coast of North America, beginning to form the Appalachians • Late: Mississippian, Pennsylvanian, Permian • 359 - 252 million years ago • Africa collides with N. Amer. Forming Pangaea and causing cooling + growth of an ice sheet over the South Pole, sea level fall, coal deposition in the mainlands, and shift from marine to continental sedimentary rocks • Giant amphibians were dominant until the evolution of reptiles during the Permian Mesozoic - • Triassic, Jurassic, Cretaceous • 252 - 266 million years ago • Pangaea begins to rift • The Atlantic is opened after a hotspot forms beneath Pangaea • Mass extinction of primate reptiles and the resulting dominance of dinosaurs during the Triassic • Archosaurs and mammals evolve Cenozoic - • Paleogene & Neogene • 66 million years ago to present • Climate cooler due to collision of India and Asia which enhanced rock weathering, lowered CO2, weakened greenhouse effect • Grass evolves, mammals flourish and diversify

A material that is _______ experiences only a small amount of ductile deformation before fracture.

brittle

sedimentary layers form in order from bottom (oldest) to top (youngest)

Superposition

The deadliest volcanic eruption in recorded history, with nearly 100,000 people killed, was the eruption of

Tambora, Indonesia in 1815

Identify and explain the relationships that exist between tectonic setting, magma composition, and type of volcano.

Tectonic setting determines the type of volcanic activity - divergent boundaries, for example, feature upwelling whereas convergent and transform boundaries do not. Magma composition is also directly related to the type of volcano - basaltic magma, for example, is found at shield volcanoes (such as Mauna Loa in Hawaii) and at cinder cones (such as Sunset Crater, in Arizona) but is not found at composite volcanoes. What magma compositions and types of volcanoes are associated with divergent or convergent boundaries? How about hot spots? why? Basalt produced by melting of mantle at divergent or convergent boundaries and hotspots. Where the crust is thin due to divergence of continental crust or thin oceanic crust, basalt is erupted with no change in its composition from passing through the crust. Basalt produces shield volcanoes if fluid and gas poor and cinder cones if frothy and gas rich. Where the crust is thick due to convergence at subduction zones or thick continental crust, fractional crystallization makes more silica rich magmas like andesite and rhyolite. Higher silica andesite and rhyolite produces composite volcanoes (stratovolcanoes) and lava domes.

Describe the types of eruption and associated volcanic hazards produced by Cascade volcanoes such as Mount Hood, Mount Rainier, and Mount St. Helens.

The Cascade volcanoes are composite volcanoes, and erupt effusively. The hazards of composite volcanoes include the initial pyroclastic flow of expelled volcanic debris, which does damage to the immediate area around the volcano and the temperature of which can melt accumulated snow and ice, leading to an event called a lahar. Lahars are slurries of snow and ice combined with expelled volcanic material which travel downstream from the volcano with immense destructive power and will destroy any structures in their path (ex. bridges). Lahars are the greatest threat posed by a future eruption of Mount Rainier - debris from a prior lahar caused by an eruption at Rainier is known to have traveled all the way to Puget Sound. Another hazard of these volcanoes is ashfall - airborne ash expelled during eruption - which can destroy structures under the weight of accumulated ash, cause harm to engines and other exposed moving parts, and even prove fatal to humans/animals if too much ash is inhaled. Additionally, if the eruption and resulting ashfall is intense enough, it has the potential to cause global cooling - such as that seen after the eruption of Mount Pinatubo - due to sulfides within the ash reflecting sunlight. Subduction zones like the Cascades produce composite volcanoes - also called stratovolcanoes - that erupt silica rich andesite and rhyolite magmas. Due to the viscous nature of silica rich magmas found at composite volcanoes like those in the Cascades, eruptions will be explosive if the magma contains gas. Once the magma degasses, the eruption becomes effusive and builds lava domes rather than flows due to the thick, pasty nature of andesite and rhyolite.

Explain how seismographs from three or more locations are used to locate the epicenter of an earthquake and determine its Richter magnitude.

The distance from a seismograph to the epicenter defines a circle of possible locations with the radius being the distance to the epicenter, but the direction is still not known so multiple three or more seismographs are used to triangulate the exact location. Circles formed by each seismograph will all intersect at a single point - the epicenter. Seismographs are also used to determine the Richter magnitude by providing the two measurements needed to determine an earthquakes placement on the Richter scale: the amplitude of the largest wave (+ deviation from horizontal) the distance to the epicenter (+ distance in arrival times of P and S waves)

8. How did the evolution of photosynthetic organisms change the Earth's atmosphere? What is the evidence for this in the rock record?

The evolution of photosynthetic organisms lead to the oxygenation of Earth's atmosphere as it weakened the greenhouse effect (heat retained in the atmosphere by CO2). The process of photosynthesis removed carbon from the atmosphere as biomass, and undecomposed biomass (fossil) was stored in sediment and rock. This resulted in an atmospheric increase of O2 and decrease of CO2, leading to widespread glaciation in the late Proterozoic, aka the Snowball Earth.

Identify and briefly define five properties of minerals that are useful for identifying a mineral. Explain which of these properties are most reliable and which are not.

The five properties useful for identifying minerals are: composition - mafic - high in iron, green to dark in color; felsic - high in silica, pink/red to light in color; and intermediate, which falls in the middle ground. texture - vitreous, metallic, etc streak - the color of the "streak" left behind when a mineral is tested against a streaking plate/tile hardness - the resistance of the mineral to being scratched; minerals can be scratched by any mineral with a higher hardness, and will scratch any mineral with a lower hardness. One of if not the most reliable property for identification. (ex. galena and graphite share the same color but have very distinct differences in hardness; graphite is much lower on the scale and streaks very easily - galena less so.) color - the observable color of a mineral. Color is the least reliable property in mineral identification given that so many different minerals share the same color. Do not confuse rocks with minerals. Texture is a property of rocks, not minerals and refers to size and arrangement of mineral grains in a rock. Crystal habit is a property of minerals and refers to the characteristic shape a given type of mineral takes and reflects its atomic structure. What you described as texture is actually called luster. Composition is also a property we used in rocks and refers to whether the rock is made mostly of dark colored, iron and magnesium bearing minerals, or light colored, sodium and potassium bearing minerals.

5. What is the geologic time scale and what is it based on?

The geologic time scale divides Earth's history into eons, eras, periods, and epochs based on major geologic events, similar rock types, and fossils.

What is the relationship between the crust and the lithosphere?

The lithosphere includes the crust, but also includes the uppermost mantle.

10. What is the Cambrian Explosion, and what caused it? Where can we find fossil evidence of this event?

The significant increase in diversity of marine invertebrates, caused by an increase in atmospheric oxygen which allowed organisms to form carbonate and phosphate for structure and support. It lead to the first animals with shells, bones, and spinal cords. Fossils from this era can be found at the Burgess Shale in British Columbia.

Which of the following statements about basalt magma is true?

basalt is NOT high in viscosity

Which of the following minerals is a sheet silicate with excellent cleavage in one direction?

biotite

Which of the following minerals is usually DARK in color?

biotite

Describe the geologic evidence that led to the discoveries of continental drift, seafloor spreading, and subduction.

Wegener initially proposed his theory of continental drift using the puzzle piece like "fit" of the continental coastlines with each other, the distribution of similar rock types across separate continents, and the distribution of similar fossils across separate continents as evidence. However, his theory was discounted due to a lack of explanation for how the continents could have moved in such a manner. Later on, many years after his death, discoveries were made about Earth's magnetism which backed up his theory. Earth's magnetism sometimes reverses, resulting in a "normal" state of polarity and a "reverse" state of polarity. While rocks are forming, the crystals align themselves with the current polarity and remain in that state, even if the Earth's polarity changes around them. After this discovery, alternating bands of crust with "normal" polarities and "reverse" polarities were able to be observed running parallel to ocean ridges. Through this, we can observe and confirm that the seafloor is growing, and since the Earth itself is not expanding, oceanic crust had to be destroyed somewhere. That was later confirmed to occur at subduction zones - places where two plates meet, and the older/denser plate is subducted beneath the other plate and destroyed, resulting in upwelling, volcanism, etc. Evidence for subduction: lack of old oceanic crust relative to continents; relationship of deep earthquakes to trenches shows where old oceanic crust is removed by subduction

In which tectonic setting does pressure increase faster than temperature, producing a low geothermal gradient and metamorphic facies indicative of high pressure and low temperature?

accretion wedge

Deep earthquakes- those that originate at depths greater than 70 km - only occur at subduction zones because

all of the choices listed here are needed to explain why deep earthquakes only occur at subduction zones

organisms which convert carbohydrates to alcohol, due to lack of available oxygen

anaerobic metabolism

A volcanic rock of intermediate composition, characteristic of subduction-zone volcanoes like those of the Cascade Range, is

andesite

bands of sedimentary rocks rich in iron oxide

banded iron formations

Mid-ocean ridge volcanism produces what type of magma?

basalt

Which of the following substances meets the definition of a mineral?

ice

The viscosity of a magma

increases with increasing silica content and decreases with increasing temperature

Which of these hazards would NOT be expected during an eruption of a shield volcano such as Mauna Loa on Hawaii?

lahars

How does earthquake magnitude differ from intensity?

magnitude reflects energy release, while intensity reflects the amount of damage

Schist-like foliation (schistosity) is seen in metamorphic rocks containing which kinds of minerals?

micas

In areas undergoing tectonic tension, such as the Red Sea, extension of the Earth's crust causes which type of fault to form?

normal

Magnetic patterns in rocks making up the oceanic crust appear as

normal and reversely magnetized strips roughly parallel to the mid-ocean ridge axis

The oldest continental rocks are nearly as old as the earth, but the oldest oceanic rocks are only about 200 million years old. This is because:

of subduction of oceanic lithosphere

The mineral ____________ is an iron magnesium silicate mineral (that recently rained down on parts of Hawaii).

olivine

In a clastic sedimentary rock, looking at ______ tells you about conditions of transportation and deposition, while looking at _______ tells you about their source.

particle size and shape, particle composition

single celled anaerobic organisms, with no cell nucleus

prokaryotes

Transform plate boundaries are marked by

two plates sliding relative to one another