geology

Some zircon minerals found in a sandstone are dated using U238/Pb206 and are found to have 70% of U238and 30% of Pb206. A) Using the graph above, construct a decay curve and use it to determine the number of half-lives that have passed since the zircon formed. B) Based on your result for Part A, calculate an absolute age for the zircon mineral, keeping in mind that the half-life of U238 = 4.468 billion years. C) Explain how this information can be used to constrain an age for the sandstone.

.a) .4 half lives b) 1.787 billion yrs (.4 x 4.4468 billion yrs) c) this info can help constrict the age of the sandstone because, assuming that no extra Pb came into the sandstone, the sandstone should be approximately 1.787 billion yrs

Compare and contrast the textures in these two photos of metamorphic rocks, and explain why they are different. What tests would you perform to conclusively identify Rock B? Propose a protolith for each rock, and state your reasoning.

1. gneiss: foliated, shale 2. quartzite: nonfoliated, to identify whether it's quartzite we could see if it scratches glass because quartzite is higher on the hardness scale than glass is; acid test: if it fizzes then it is marble, but if it does not then it is quartzite. Quartz sandstone. the top rock is flatter and has dark layers. the main reason they are different is that gneiss is a foliated rock meaning that it has parallel surfaces and/or layers.

(a) If each sediment in the photos below became a rock, what would be the name for each rock formed? Explain your reasoning. (b) Generally speaking what are the relative distances from the source that each sediment was transported, and the relative energy of the water during deposition? Explain your answer, referring to observations of sorting, rounding, and other features in the photos.

1. quartzite because it forms from the metamorphism of pure quartz sandstone. 2. shale because it is made of clay 3. biochemical limestone because it forms in marine environments where shells are located 4. conglomerate bc coarse grained and includes feldspar and sand. B) quartzite-medium distance and water bc of semi-roundness shale- deep in the water biochemical- deep in the water conglomerate- transported semi-distance bc rouned, but coarse grained.

(a) Identify each of the rocks shown below (Rocks 1 - 4), and describe the observations that served as the basis for your identification. You must fully explain your reasoning for full credit. (Note: The shiny reflection of Rock 3 is caused by abundant, coarse muscovite.)(b) In the gray boxes displayed on the cartoon of a mountain interior (below), show where each of the rocks from part (a) is likely to occur. Explain your reasoning.

1. shale- marine environment bc of prints 2. slate- layers 3. schist - large mica flakes 4. gneiss- it is always foliated; dark and light layers B) shale-in the ocean, deep waters, slate-low pressure and temperature, schist- metamorphism of mudstone/shale, gneiss-high temperatures and pressures

Identify the structures shown on the two diagrams below. Include arrows that show relative motion, and identify hanging and footwalls, if appropriate.

1. strike-slip fault 2. normal fault

unconformity

A boundary between two different rock sequences representing an interval of time during which new strata were not deposited and/or were eroded. examples of unconformities include angular unconformity, nonconformity, and disconformity.

gneiss

A compositionally banded metamorphic rock typically composed of alternating dark- and light-colored layers. The gneiss banding gives it a striped appearance.

thrust fault

A gently dipping reverse fault. the hanging-wall block moves up the slope of the fault.

schist

A medium-to-coarse-grained metamorphic rock that possesses schistosity. It is a type of foliated metamorphic rock.

marble

A metamorphic rock composed of calcite and transformed from a protolith of limestone. during the formation of marble, calcite composing the protolith recrystallizes, so fossil shells, pore space, and the distinction between grains and cement disappear.

shadow zone

A seismic shadow zone is an area of the Earth's surface where seismographs can only barely detect an earthquake after its seismic waves have passed through the Earth. When an earthquake occurs, seismic waves radiate out spherically from the earthquake's focus.

reverse fault

A steeply dipping fault on which the hanging-wall block slides up. reverse faults accommodate shortening of the crust.

shear stress

A stress that moves one part of a material sideways past another part. most common stress at transform plate boundaries.

A. What is the prominent feature in the photo below? Briefly describe how it formed by referring to observations in the picture and your knowledge of how sediment is transported and deposited. B. For this photo, describe how and why the grain size and roundness of sediments on the valley bottom may vary with distance from the base of the mountains. Also explain why the white material in the foreground of the photo may have formed. Fully explain your reasoning.

A) Alluvial fans occur at mountain fronts, where a fast moving stream empties onto a plain. however, in arid regions where there is not enough water for the stream to flow continuously, the sediment is deposited at the mountain front in a wedge-shaped apron of gravel and sand. B) the further the sediment is from the base of the mountain, the finer and rounder it will be. coarser at the valley (bc small and at an angle) the white stuff is evaporite material such as salt. (evaporite-a natural salt or mineral deposit left after the evaporation of a body of water)

. A) In our tumbling experiment, the rain water that interacted with our mineral and rock samples had an initial pH of ~4.99 and initial specific conductance of ~7 uS/cm. How did pH and specific conductance of the rain water change after the tumbling experiment? Why did this happen? B) How might these observations explain why most rivers have a neutral pH (>7)? Since most rivers flow to the ocean, how might our observations explain why ocean water is salty?

A) Both the pH and the specific conductance increased. The pH changed because the chemical weathering the rocks and minerals were undergoing neutralize the acidity in the rain- new minerals and substances were added to the water as the original rocks and minerals broke down, making the water more neutral. Specific conductance(how well water can conduct an electrical current) increased because the dissolution of the rocks and minerals increased the amount of ions in the water.

A) Explain the difference between physical and chemical weathering. B) What processes can cause originally solid rock to break into pieces and what are the various reactions that can contribute to chemical weathering? In your answer, give two examples of physical weathering and two examples of chemical weathering processes and explain how each occurs.

A) physical weathering is the process in which intact rock breaks into smaller grains or chunks. Physical weathering includes jointing, frost wedging, and salt wedging. chemical weathering is the process in which chemical reactions alter or destroy minerals when rock comes in contact with water solutions and/or air. This includes dissolution, hydrolysis, and oxidation. B) One type of physical weathering that breaks rock is jointing. Joints are natural cracks that form in rock due to the removal of overburden or due to cooling. The removal of overburden is caused by erosion, and with less pressure comes cooler temperatures. Another type of physical weathering includes thermal expansion. In thermal expansion, heat can expand a layer of rock and upon cooling, the layer contacts. Consequently, forces that have been created bc of this change cause the outer part of the rock to break off in sheet like pieces. One type of chemical weathering is dissolution. Dissolution causes minerals to dissolve in water. This can cause holes in the rock. Another type of chemical weathering is hydrolysis. During hydrolysis, water chemically reacts with minerals and breaks them down to form other minerals. This weakens the mineral and makes it less resistant to weathering.

Below is a photo of a landscape from the western U.S. A) Why do the different sedimentary layers making up the canyon wall have different slopes? B) Why are these rocks red, and what does that color suggest about the weathering that occurred when the sediments were deposited in the geologic past?

A) they have different slopes due to differential weathering which is what happens when different rocks in an outcrop undergo weathering at different rates. B) The red color is due to the presence of iron. Through oxidation, the rocks "rust" and get this color. this says that the weathering occurred before the sediments were deposited.

. A). The cartoon below illustrates changes in sediment from coast to deeper ocean. Explain why this change in sediment type occurs. B) Which rock outcrop would represent the a previous environments from the geologic past represented by the cartoon? Note the features in the photo that support your conclusion. C) If a marine regression occurs, resulting in a significant drop in sea level, what sequence of sedimentary layers would you expect to overlay the limey deposits in the cartoon? Explain your answer.

A) this change in sediment occurs because the sand is located in the shallow end because there is less water so it is not as fine. The mud is next because of sediment from the ground. Next comes the limey outcrop and this is due to the foraminifera. B) A is the limestone because of the zoom in of the foraminifera. B is the sandstone because there is wave action there. C is mud because mud gets deposited in still water. C) marine regression is a geological process occurring when areas of submerged seafloor are exposed above the sea level. sea level is dropping. If a marine regression occurs, then the coastline moves out and the mud with be on top of the limestone and the sand will be on top of the mud (hence sand, mud, lime from top to bottom).

Explain why uplift and erosion that reveals rocks that have been buried in Cartoon A produce the cracks shown in Cartoon B.

During exfoliation, large granite plutons like the ones in these images, may split into sheets along the joints parallel to the face of the mountain. Erosion and jointing allow sedimentary rock beds to break into rectangular blocks. As seen in Cartoon B, these blocks then topple over and uplift exposes the granite .

slate

Fine-grained, low-grade metamorphic rock, formed by the metamorphism of shale. It is formed at relatively low temperatures and pressures.

a. Determine the relative ages of rocks making up the Grand Canyon area based on the cross section shown. Put your answer in the form of a list with the appropriate stratigraphic principle written next to each choice. List the oldest geologic event on the bottom, and the youngest on top. Note that the Zoroaster = granite. And the Brahma and Vishnu Schist = metamorphic rocks. The remaining rock formations are sedimentary. Note: If the timing of some events has more than one interpretation, then bracket on your list a time range under which the event could have occurred.

INNER GORGE- erosion kaibab - superposititon toroweap - superposition coconino - superposition supai - superposition erosion - disconformity redwall - superposition erosion - disconformity muav - superposition bright angel shale - superposition tapeats - superposition erosion - nonconformity (left), angular (right) tilting - principle of original horizontality Hakata - superposition Bass - superposition Shinumo - superposition erosion - nonconformity faulting - only cuts through zoraster and older Zoraster - crosscutting relations Brahma - superposition V.S. - superposition

foliation

Layering formed as a consequence of the alignment of mineral grains, or of compositional banding in a metamorphic rock. The most common types of foliated metamorphic rock include slate and gneiss.

Explain why seismic waves refract as they travel through the Earth. How do seismic data inform geologists that the outer core of the Earth is liquid? Explain your answer fully, using sketches that show the interior structure of the Earth.

Seismic waves refract as the waves travel through the earth due to changes in velocity as waves travel down. Seismic data shows that the outer core is liquid because both p-waves and s-waves can go through solids. However, only p-waves can go through liquids so geologists can see that the outer core is liquid because s-waves do not go through.

elastic-rebound theory

The concept that earthquakes happen because stress builds up, causing rock adjacent to a fault to bend elastically until breaking and slip on a fault occurs. the slip relaxes the elastic bending and decreases stress.

outer core vs inner core

The core is the dense, iron rich center of the Earth. The outer core is consists of liquid iron alloy. It is a liquid because the temperature in the outer core is so high that even the great pressures squeezing the region cannot keep the atoms in place. The inner core consists of solid iron alloy. It is solid because it is deeper and is subjected to even greater pressures.

earthquake focus vs epicenter

The focus is the place within the Earth where rock ruptures and slips, or the place where an explosion occurs. Energy radiates from here. The point on the of the Earth that lies directly above the focus is the epicenter.

earthquake focus

The location where the earthquake begins. the closer it starts to earth's surface, the more damage it can cause.

lithosphere

The relatively rigid, nonflowable, outer 100- to 150-km-thick layer of the Earth, constituting the crust and the top part of the mantle. Oceanic lithosphere is thinner than continental lithosphere.

crust

The rock that makes up the outermost layer of the Earth. There are two types of crust: continental and oceanic crust.

A) What is the geologic term for the cracks shown in photo A? How do they form, and what kinds of processes might make them bigger with time? B) Photo B shows cracks in a limestone, versus the granite shown in Photo A. Describe why the cracks in Photo B result in their observed shape.

The term for the cracks in picture A are called joints. They form due to the removal of overburden or due to cooling in rocks. Joints can get bigger through erosion which removes some of the rock near joints. The cracks in photo B result in their observed shape due to chemical weathering of limestone. The dissolution of the calcite in the limestone causes the round edges of the joints. As dissolution continues, the joints continue to widen.

arkose

a clastic sedimentary rock containing both quartz and feldspar grains. This is a type of clastic sedimentary rocks.

normal fault

a fault in which the hanging-wall block moves down the slope of the fault. normal faults accomodate stretching of the Earth's crust, as happens during rifting.

mudcrack

a fracture caused by the drying out and shrinking of silt or clay. this is a type of bed-surface marking.

alluvial fan

a gently sloping apron of sediment dropped by an ephemeral stream at the base of a mountain in arid or semiarid regions. It is formed by a fast-moving stream that abruptly emerges from a mountain and the water spreads over a broad surface.

marine transgression

a geologic event during which sea level rises relative to the land and the shoreline moves toward higher ground, resulting in flooding. Transgressions can be caused either by the land sinking or the ocean basins filling with water.

marine regression

a geological process occurring when areas of submerged seafloor are exposed above the sea level. The opposite of this is marine transgression. sea level is dropping

quartzite

a metamorphic rock composed of quartz and transformed from a protolith of quartz sandstone. during metamorphism, preexisting quartz grains recrystallize, creating new, larger grains.

dissolution

a process during which materials dissolve in water. Dissolution primarily affects salts and carbonate minerals.

metamorphic grade

a representation of the intensity of metamorphism, meaning the amount or degree of metamorphic change. classification depends primarily on temperature because temperature plays the dominant role in determining the extent of recrystallization.

compressive stress

a set of stress directed toward the center of a rock mass (a rock is squeezed). horizontal compression drives collision

right-lateral strike-slip fault

a strike slip fault in which the block on the opposite fault plane from a fixed spot moves to the right of that spot. these occur at transform plate boundaries.

nonconformity

a type of unconformity at which sedimentary rocks overlie basement (older intrusive igneous rocks and/or metamorphic rocks). the igneous or metamorphic rocks underwent cooling, uplift, and erosion prior to becoming the substrate.

tsunami

a wave produced by displacement of the sea floor. the displacement can be due to an earthquake, submarine landslide, or volcanic explosion.

delta

a wedge of sediment that accumulates where moving water enters standing water. These form at the mouths of streams that empty into lakes.

The cartoon above shows a sequence of sedimentary rocks with some basalts. (Note rock labels on diagram.) a) What methods could you use to try to constrain the ages of these rocks? Where might you be able to determine numeric ages, and where could you only determine relative ages? Explain your answer. b) The basalts have been radiometric dated as follows: basalt dike = 20 million years old; basalt lava = 25 million years old. Using relative age dating principles, do these results make sense? Explain. c) Some index fossils (ammonites) in the shale layers (the ones that are deeper than the sandstone) indicate that these shales are from the same geologic time period. The index fossils went extinct more than 65 million years ago. The limestone unit contains older ammonites that went extinct 80 million years ago. Based on this evidence, should the basaltic lava be reinterpreted as a basaltic sill? Explain your reasoning.

a) oldest- limestone, shale, basaltic lava, shale, sandstone, shale, basaltic dike. yes, you can if you find out which radio active elements and use half life-for basalts. b) yes it makes sense bc the dike is younger than the lava. c) yes, because based on part b, the lava is 25 million yrs old. d) no, because it would make it older than the shale and sandstone. this means that zircons, by some event, were added to the sandstone, making it seem older than it actually is.

numeric age dating

aka absolute age. the age of a geologic feature given in years.

alluvial fan vs delta

an alluvial fan is a gently sloping apron of sediment dropped by an ephemeral stream at the base of a mountain in arid or semiarid regions. a delta is a wedge of sediment formed at a river mouth when the running water of the stream enters standing water, the current slows, the stream loses competence, and sediment settles out.

angular unconformity

an unconformity in which strata below were tilted or folded before the unconformity developed; strata below the unconformity therefore have a different tilt than the strata above. An angular unconformity cuts across the underlying layers.

disconformity

an unconformity parallel to the two sedimentary sequences it separates. layers of sediment accumulate, sea level drops and erosion occurs, and sea level rises and new sedimentary layers accumulate.

radioactive isotopes

an unstable isotope of a given element. the isotope of an element has the same atomic number but a different weight.

Nonconformity vs Disconformity

both nonconformities and disconformities are types of unconformities, or a surface representing a period of nondeposition and possible erosion. in a nonconformity, sedimentary rocks overlie generally much older intrusive igneous and/or metamorphic rocks. a disconformity is an unconformity parallel to the two sedimentary sequences it separates.

Explain what the two diagrams below illustrate and their significance for understanding the physical differences within the interior of the earth. In your answer, explain the different kinds of seismic body waves and why the seismic rays make the different paths. (note this question is very similar to #19.)

both p-waves and s-waves can go through solids. However, only p-waves can go through liquids so geologists can see that the outer core is liquid because s-waves do not go through. the lines are bending because waves refract as they travel through the different layers of earth because they are composed of different things. in the shadow zones, the earth does not receive those specific waves.

breccia vs conglomerate

breccia is a coarse sedimentary rock consisting of angular fragments; or rock broken into angular fragments by faulting. conglomerate is a very coarse-grained sedimentary rock consisting of round clasts. breccia indicates that it hasn't been transported very far while conglomerate has (hence rounded pebbles).

clastic sedimentary rock vs chemical sedimentary rock

clastic sedimentary rocks consist of cemented together clasts, solid fragments and grains broken off of preexisting rocks while chemical sedimentary rocks are made up of minerals that precipitated directly from water solutions. Chemical sedimentary rocks typically have a crystalline structure. clastic ex. sandstone chemical ex. dolostone

breccia

coarse sedimentary rock consisting of angular fragments; or rock broken into angular fragments by faulting. A lot of breccia has poor sorting.

P-wave

compressional seismic waves that move through the body of the Earth. P-waves travel the fastest; thus, they arrive first.

siltstone

fine-grained sedimentary rock generally composed of very small quartz grains.It has a "fine" clast size.

A) How do grain size and shape, sorting, and roundness/angularity of sediments change as they are transported downstream? B) Compare how sediment in an alluvial fan differs in size, shape, sorting, and composition from sediment in a deep-marine deposit. Explain the sedimentary processes that account for differences in these two types of environments.

grain size decreases, sorting becomes more well sorted, more rounded B) Alluvial fans occur at mountain fronts, where a fast moving stream empties onto a plain. however, in arid regions where there is not enough water for the stream to flow continuously, the sediment is deposited at the mountain front in a wedge-shaped apron of gravel and sand. Here there is coarse sediment, not well sorted, conglomerate. In deep-marine deposits, currents deposit graded beds. only plankton and fine clay provide sources for sediment. mudstones, chalk shells, and chert then form. small size, well sorted, shape is fine.

principle of inclusions

if a rock contains fragments of another rock, the fragments must be older than the rock containing them. a conglomerate containing pebbles of basalt is younger than the basalt.

principle of superposition

in a sequence of sedimentary rock layers, each layer must be younger than the one below, for a layer of sediment cannot accumulate unless there is already a substrate on which it can collect. The layer on the bottom is the oldest and the layer on the top is the youngest.

Using the diagram below, explain how changes in velocity of p-waves relates to physical differences within the crust and mantle. Where on the diagram is the asthenosphere, and how does the p-wave velocity show its location?

in the mantle, the waves moves at a faster velocity because the rock is more dense. The outer core has a lower velocity than the mantle because it is less dense (since it is liquid). the asthenosphere is where it says "lower mantle" and the velocity increases because the asthenosphere is relatively soft and can flow.

For the cartoon above, report numeric or relative ages as appropriate, and list the geologic eon or era when these rocks formed, for formations: P, B, R, M, H. Use the following information to help: Unit P has 75% of original K40 remaining, and Unit M has 80% of original K40. The halflife for K40 decaying to Ar40 is 1.3 billion years. In solving your answer, construct the decay curve for K40 on the graph below. Report your results in millions of years. Show all work and calculations for deriving your answer.

isnt relative age the same thing as the top? geologic era: B: P: .625 billion years R: M: .5625 billion years H: all formed in the proterozoic eon?

principle of horizontality

layers of sediment, when originally deposited, are fairly horizontal. if sediments were deposited on a steep slope, they would likely slide downslope before they could be buried and lithified.

jointing

natural cracks that form in rocks due to the removal of overburden or due to cooling. Changes in pressure and temperature caused by erosion which causes pressure and temperature to decrease, are a cause of jointing.

What is the order of geologic events that produced this sequence of rocks in the cartoon below? Make a list with the oldest event on the bottom of your list. Next to each event, name the stratigraphic principle you used to base your conclusion. Ignore Unit G.

oldest---- P: superposition F: cross-cutting? erosion: tilting B: superposition R: superposition M: cross cutting? H:superposition A: superposition erosion: angualar unconformity E: superposition X: superposition D: superposition K: fault J: superposition S:?

Provide a metamorphic rock name for each description below. What is the name of a protolith for each metamorphic rock? Description Foliated rock with alternating bands rich in quartz and feldspar or biotite, garnet, and sillimanite. Shiny, foliated rock rich in muscovite and biotite, with numerous crystals of coarsegrained garnet. Nonfoliated rock consisting entirely of fine-grained recrystallized quartz. Foliated rock with fine-grained muscovite interspersed with some clay. Rock composed of recrystallized calcite and is mostly nonfoliated. Some faint bands might be visible if the parent rock contained some mineral impurities.

one: gneiss, shale two: schist, shale third: quartzite, quartz sandstone fourth: phyllite, shale fifth: marble, limestone

p-wave vs s-wave

p and s waves are types of seismic waves. p-waves are compressional body waves, meaning that they cause particles of materials to move back and forth parallel to the direction in which the wave itself moves. s-waves are shear body waves. s-waves, because they are body waves, pass through the interior of the Earth. As shear waves, they cause particles of material to move back and forth perpendicular to the direction in which the waves itself moves.

body seismic waves

pass through the interior of the Earth. body waves arrive before surface waves.

uniformitarianism

physical processes that operate in the modern world also operated in the past, at roughly the same rates, and these processes were responsible for forming geologic features preserved in outcrops. Individual geologic features took a long time, and that not all features formed at the same time, so the Earth must have a history that includes a succession ow geologic events.

4. Our tumbling experiment simulated physical and chemical weathering of geologic materials in contact with rain water. Based on our simulation, describe how each material responds (if any) to both physical and chemical weathering: a. Minerals: quartz, calcite, halite b. Rocks: basalt, shale

quartz- the quartz had the strongest resistance to physical weathering, but was still affected by it slightly. It was also slightly affected by chemical weathering because of dissolution. calcite- the calcite was affected by chemical weathering because dissolution affects carbonate minerals. halite- the halite undergoes chemical weathering through dissolution basalt- the basalt underwent physical weathering shale- the shale underwent physical weathering as shown my the rounded edges on the product of this experiment

quartzite vs gneiss

quartzite forms by the metamorphism of pure quartz sandstone. During metamorphism, preexisting quartz grains recrystallize, creating new, larger grains. It is a nonfoliated rock. Gneiss is a compositionally layered metamorphic rock, typically composed of alternating dark-colored and light-colored layers that range in thickness from millimeters to meters.

ripple marks

relatively small, elongated ridges that form on a bed surface at right angles to the direction of current flow. these can be found on modern beaches and preserved on bedding planes of ancient rocks.

ripple marks vs mud cracks

ripple marks are relatively small, elongated ridges that form on a bed surface at right angles to the direction of current flow. These can be found on modern beaches and preserved on bedding planes of ancient rocks. Mud cracks are the openings between the hexagonal plates that form in mud when it dries up and cracks after deposition.

clastic sedimentary rock

sedimentary rock consisting of cemented-together detritus derived from the weathering of preexisting rocks. An example of this is sandstone.

(bio)chemical sedimentary rock

sedimentary rock formed from material (such as shells) produced by living organisms. These rocks can be found in and near bodies of water.

S-wave

seismic shear waves that pass through the body of the Earth. S-waves travel about 40% slower than P-waves, so they arrive later.

tensional stress

stress which stretches rocks in two opposite directions (the rock is pulled apart). The rocks become longer in a lateral direction and thinner in a vertical direction.

wave refraction

the bending of waves as they approach a shore so that their crests make no more than a 5 degree angle with the shoreline. it decreases the angle at which waves move close to shore.

daughter isotope

the decay product of radioactive decay. The parent isotope is the isotope that undergoes decay.

core

the dense, iron-rich center of the Earth. The inner core is a solid iron alloy while the outer core consists of liquid iron alloy.

mainshock

the largest earthquake in a sequence. Sometimes preceded by foreshocks and sometimes followed by aftershocks.

asthenosphere

the layer of the mantle that lies between 100-150 km and 350 km deep; the asthenosphere is relatively soft and can flow when acted on by force. The asthenosphere lies below the lithosphere.

oxidation

the loss of electrons during a reaction by a molecule, atom or ion. Oxidation with iron-bearing minerals can rust.

epicenter

the point on the Earth's surface directly above the focus of an earthquake. the greatest damage tends to take place here.

exfoliation

the process by which an outcrop of rock splits apart into onion-like sheets along joints that lie parallel to the ground surface. this is a form of jointing.

chemical weathering

the process in which chemical reactions alter or destroy minerals when rock comes in contact with water solutions and/or air. This includes dissolution, hydrolysis, and oxidation.

physical weathering

the process in which intact rock breaks into smaller grains or chunks. Physical weathering includes jointing, frost wedging, and salt wedging.

hydrolysis

the process in which water chemically reacts with minerals and breaks them down.Hydrolysis reactions in feldspar produce clay.

aftershock

the series of smaller earthquakes that follow a major earthquake. aftershocks happen bc slip during the mainshock does not leave the fault in a perfectly stable configuration.

foreshock

the series of smaller earthquakes that precede a major earthquake. these happen before the mainshock and aftershock.

mantle

the thick layer of rock below the Earth's crust and above the core. the mantle is made up of the upper mantle and the lower mantle.

half-life

the time it takes for half of a group of a radioactive element's isotopes to decay. the daughter isotope number gets larger while the parent isotope number decreases.

evaporite

thick salt deposits that form as a consequence of precipitation from saline water. the type of salt mineral depends on the amount of evaporation.

surface seismic waves

travel along the Earth's surface. surface waves arrive after body waves.

conglomorate

very coarse-grained sedimentary rock consisting of rounded clasts. A lot of conglomerate rocks have poor sorting.

shale

very fine-grained sedimentary rock that breaks into thin sheets. Shale has a very fine clast size.

spheroidal weathering

weathering that causes the corners and edges of rock to be more rounded. This happens because weathering attacks a corner from three directions.

differential weathering

what happens when different rocks in an outcrop undergo weathering at different rates. This can cause cliffs to have a stair-step shape.

principle of baked contacts

when an igneous intrusion "bakes" (metamorphoses) surrounding rock. the rock that has been baked must be older than the intrusion.

11. The photo to the right shows a sedimentary rock sequence from the Grand Canyon. All the rocks contain fossils of marine organisms, indicating that the sediments were once deposited in an ocean. (a) What are the relative ages of the rock formations, and which relative age dating principle was the basis for your answer? (b) How did the marine environment change through time to cause deposition of these three sedimentary rock formations? Explain your answer in terms of the kinds of sediment that make up these rocks and where the sediment was deposited relative to a shoreline (e.g. shallow vs. deep water).

youngest to oldest bc of superposition: limestone, shale, sandstone. B) a marine transgression occurred (like question above)