Exam II Review Flashcards
How old is the Earth?
4.565 Ga
Order of eras
(youngest to oldest) Cenozoic, Mesozoic, Paleozoic
Meaning of ka, Ma, Ga
thousands, millions, billions
What distinguishes the mechanical layers? How do they relate to the compositional layers?
Lithosphere: rigid solid (crust and upper mantle, including Moho)
Asthenosphere: weak solid (mantle)
Outer core: liquid (core)
Inner core: solid (core)
The lithosphere is primarily oxygen/silicon/aluminum/magnesium, the asthenosphere is primarily oxygen/silicon/magnesium, the outer core is mostly liquid iron, and the inner core is mostly solid iron.
What layers within the Earth are liquid?
Outer core
Differences between continental and oceanic crust
Continental: less dense, thicker, more buoyant, plagioclase feldspar (must abundant mineral)
Oceanic: thinner, more dense, made of basalt and gabbro
About how fast do plates move?
1-15 cm/yr
Types of plate margins and most highlighted examples of each
Convergent: north american plate meeting pacific plate
Divergent: mid atlantic ridge, east african rift
Transform: fracture zones around mid atlantic ridge
Volcanism, earthquakes, and mountains at different kinds of plate margins (info in the table)
table, bitch, table
Where are volcanic arcs formed? Know highlighted examples
Subduction zones (either oceanic subducts continental or oceanic subducts oceanic)
Mariana Islands, Cascades, Andes
What is the difference between a theory and a hypothesis?
Hypothesis: An explanation for observations to be tested (may be supported, not confirmed)
Theory: An explanation for observations that have been tested numerous times and is supported by evidence
What are the four components of the definition of a mineral used in lecture?
1) solid
2) naturally occurring
3) crystalline structure
4) definable composition
Cleavage vs crystal form (how are they different?) Why is one more useful than the other?
Cleavage: a mineral breaking on planes of atomic weakness
Crystal form: how a mineral grows unimpeded (has crystal faces)
Cleavage is more useful bc most minerals don’t have a perfect environment to grow unimpeded in
Most abundant mineral in crust of the Earth
fuckin plagioclase feldspar
In order, what are the two most abundant elements in the crust and the Earth as a whole?
Crust: oxygen, silicon
Earth as a whole: iron, oxygen
What are the three rock types, what differentiates them, and what are their rock forming processes?
1) Igneous: made from magma
2) Metamorphic: recrystallizing in solid state
3) sedimentary: rock fragments/dissolved rock components compacted on surface
Origin of mafic versus felsic magma
Mafic magma comes from mantle (50% SiO2)
Felsic magma comes from crust (75% SiO2)
How do we interpret grain size in igneous rocks? (cooling rate and depth)
Larger grains form at a slower cooling rate deeper w/in earth
Small grains form at fast cooling rate at or near surface of earth.
Which is more explosive, basaltic magma or rhyolitic magma? Why?
Rhyolitic magma is more explosive because its high viscosity traps more dissolved gas and keeps it at a higher pressure than the atmosphere
What kinds of volcanoes are created by effusive and explosive eruptions of basaltic, andesitic, and rhyolitic lava?
Effusive Basalt: shield
Effusive Andesitic: composite
Effusive rhyolitic: dome
Explosive basalt: cinder cones
Explosive Andesitic: composite
Explosive rhyolitic: calderas
be able to recognize all of these in photos
What is the leading cause of fatalities in volcanic eruptions?
pyroclastic flows
What are the two types of weathering? Examples of each?
Physical: frost wedging, root wedging
Chemical: dissolution, hydrolysis, oxidation, hydration (creates clay minerals like Kaolinite)
Relationship between grain size and surface area to volume ratio (reading)
Small grain size means high surface area to volume ratio 🤷🏻♀️
What is soil?
Unconsolidated geologic material that has been modified at Earth’s surface by weathering and addition of organic material
What group of minerals is a product of weathering and common in soils?
Clay minerals
Order of the five horizons in soil
OAEBC
Origin of O and E horizons
wet conditions (that’s what she said)
O is top soil with organic material
E is transition soil
How do soils vary according to latitude, slope, and age?
Latitude: thin soils in desert, thick/organic in tropical conditions, slow chem weathering in arctic (chem weathering happens at high temps)
Slope: accumulates at base of slopes, closer to oceans/shores etc
Age: the older, the thiccer (the younger, the thinner, the less organic)
What are the key nutrients in soil
Nitrogen
Phosphorus
Potassium
What, and when, was the dustbowl
A period of massive windblown soil loss in the 30s
What is the SD state soil?
Houdek soil
a loam
old glacial deposits -> thousands of years as a grassland
Four classes of sedimentary rocks:
clastic, chemical, biochemical, organic
What are the two aspects of lithification, turning sediment into sedimentary rock?
compaction + cementation (but also be aware of physical and chemical weathering, I think?)
What are the grain size boundaries for sand/sandstone? (mm)
1/16-2 mm
What is the concept of uniformitarianism; what are simple examples of its application?
Definition: processes we see active today were active in the past and explain analogous characteristics observed in rocks
ex: crossbedding=sand dunes, poor sorting and striations=prolly glaciers?
What is the basic unit of mapping sedimentary rocks?
formation: a mappable unit of related beds
- formations are basic units of geologic maps
Know what sedimentary rocks are clastic, chemical, biochemical, and organic
Clastic: conglomerate, breccia, sandstone, mudstone, arkose, siltstone, shale
Chemical: evaporites (halite and gypsum), some limestones and cherts, travertine
Biochemical: most limestones, most cherts, carbonate rocks containing calcite, chalk, fossiliferous, micrite
Organic: coal, oil shale
What are transgressions and regressions? (Be able to to recognize sequence as presented in lecture)
Trans: when the sea advances upon the land
Regs: retreat of the sea from the land’s surface
Sequences to recall:
- trans: (from top to bottom) limestone-shale-sandstone
- regs: (from top to bottom) sandstone-shale-limestone
so wherever sandstone is determined where the ocean STARTED
Know the highlighted feature of rocks distinctive to each of the following paleo-environments: dunes, glaciers, streams, swamps, deep open oceans, and arid lakes
Dunes: grains are pocked/frosted, large cross beds
glaciers: poorly sorted boulder conglomerates, glacial striations, boulders floating in silt and clay
streams: conglomerates, sandstones, shales, channels in beds, cross bedding, current ripples
swamps: coal, lots of organic material and water
deep open oceans: shales and bedded cherts (silica shells accumulating)
lakes: thin beds of shale, wave ripples, rain drop impressions, mud cracks, halite and gypsum (evaporites)
Know two sedimentary structures that can be used to determine paleocurrent directions (and be able to tell direction based on a picture of cross beds)
crossbedding and ripples
General aspects of the two highlighted ways in which tectonics creates sedimentary basins
convergent boundaries: compressional thrust faulting and folding creates foreland basins (Appalachian Basin)
divergent boundaries: extension from tectonic divergence causing faulting in which some blocks are down-dropped…creates continental rift basins (Newark Basin)
How is metamorphism different from igneous processes?
It recrystallizes in the solid state, not the liquid state
How does foliation orientation relate to directions compressional tectonic stresses?
Foliation orientation forms perpendicular to tectonic stress
General ideas of metamorphic grades and facies
grade: conditions of pressure and temp (low, intermediate, high)
facies: fields on a PT graph that are named after some rocks that form there
Basics of two “environments” of metamorphism discussed in lecture
1) contact metamorphism (heat from igneous intrusion)
2) regional metamorphism: heavy on pressure and temp
What makes a good metamorphic index mineral? (be able to distinguish good and poor index minerals on a diagram)
A ‘good’ index mineral is one that has a limited PT range of stability and defines its conditions more narrowly
What controls the mineralogy of a metamorphic rock?
The starting material (protolith) and the conditions of metamorphism (pressure, temp)
Know plausible protoliths for marble, quartzite, and amphibolite
marble: limestone
quartzite: sandstone
amphibolite: basalt
Recognize schist vs gneiss vs quartzite in pics
schist has lots of foliation, gneiss is banded, and quartzite has neither/looks more grainy
Know the sequence of four metamorphic rocks created by progressive metamorphism (low to high grade) of a shale protolith
With shale as protolith (from low to high) we have…
1) slate
4) phyllite
3) schist
4) gneiss
Two settings in which we find extensive exposures of metamorphic rocks
1) shields (Canadian Shield)
2) exhumed orogenic belts (Black Hills)
Where do we find metamorphic rocks in SD?
Black Hills (specifically Custer, SD)
Epicenter vs focus (hypocenter)
Focus/hypocenter: the place inside Earth’s crust where an eq originates
Epicenter: The point on the Earth’s surface directly above the focus
Characteristics of eqs at different plate tectonic boundaries
Subduction zones: most powerful, can be deepest (Wadati Benioff)
Mid-ocean ridges: very shallow and weak
Transform fault zones: powerful, shallow
Continental collision: powerful, deep
Where is the greatest concentration of intraplate eqs in the US? Why there?
New Madrid, Missouri (failed rifts from Precambrian and Mesozoic)
-crust is stronger in intraplate eqs and can transmit lots of energy
Be able to roughly determine distance from an eq using seismometer record
1) find out delay time
2) look for where the delay time (vertical axis) is the same size between the two lines on the graph
Characteristics of different types of seismic waves
Surface (rayleigh and love): slow, on surface, undulating water motion
S-Waves: shear motion perpendicular to ray path, moves thru interior, undulating water motion, can’t go thru liquid
P-waves: compression-motion parallel to ray path, move thru liquid, fastest waves
Difference between magnitude and intensity
Magnitude: measure of energy
Intensity: measure of the effect on humans
Difference between richter magnitude and moment magnitude
Richter: based on local seismograph measurement
Moment: represents actual energy release
how much more energetic is an earthquake 1 magnitude than another? Difference of 2? etc
32x increase per magnitude (going up twice would be 1000x, 32 x 32)
Basics of damaging secondary effects of earthquakes
fires, liquefaction, landslides, subsidence/lift, tsunamis
At what kind of plate tectonic boundary are the greatest tsunamis generated? Why?
subduction zones (thrust faults); sudden vertical displacement of sea flow, pushes water up and down up and down
Several parts of the US are most subject to tsunami hazards, where?
Washington + Oregon (pacific northwest), as well as CA, Hawaii, and Alaska
What causes large local variations in shaking by earthquakes (eg, the San Francisco Bay Area eq in 89)
amplification of seismic waves in sediments
How good are we at forecasting specific timing of earthquakes?
We can make long term predictions but not short term ones
What are the three elements of long-range earthquake forecasts?
1) probability
2) specified magnitude
3) defined period of years
Most fatal, most costly, and most powerful earthquakes?
Most fatal: Shaanxi China 1556 830,000 killed
Most costly: Japan 2011 $360 billion damage
Biggest: Chile 1960, M 9.5
EQ in US that did tremendous damage via fire?
1906 San Francisco
Types of Faults (identify in photos)
normal (hanging wall block goes down, foot wall block goes up)
reverse
thrust
strike slip
Fault activity
active: movement in past 12 ka
potentially active: active in 2.6 Ma but not last 12 ka
inactive: no activity in 2.6 Ma
Different ways that we learn about the interior of the earth
Seismic wave fronts and travel times, reflection and refraction of wave energy, magnetism, gravity
what kind of seismic waves are not transmitted through a fluid/liquid
S waves cannot go through liquid/fluid
What is refraction?
the bending of a ray as it passes through a boundary between two different materials
What is the Moho?
crust-mantle boundary
How do seismic waves refract when they speed up?
If a ray passes into a layer in which it travels more rapidly, it would bend up and toward the boundary
The “low velocity zone” LVZ corresponds to what mechanical layer?
The asthenosphere! (specifically under the oceanic lithosphere!)
What does the S wave shadow zone tell us?
that s waves can’t pass through the core/liquid/fluid
Is there a P wave shadow zone?
Yes, bitch, there is. It’s caused by the waves’ velocity slowing down as it passed through the fluid of the outer core.
What does seismic tomography tell us?
it creates a 3D image of variations in seismic-wave velocities within the earth to understand where waves will speed up and slow down (with anomalies of course)
Use of seismic reflection studies
often used by gas and oil companies bc it defines subsurface bedding, stratigraphic formation contacts, folds, and faults
