Exam 1 Flashcards
Memorize by 2/25
Can science prove anything? Explain.
No, because we cannot confirm that the pattern will always repeat itself the same way. Instead, scientific data either supports or rejects our hypotheses
What does a scientific hypothesis have to be?
They must be falsifiable, meaning they can be supported or rejected using data but never proven. A hypothesis that isn’t falsifiable or testable is merely speculative
What is the difference between a law and a theory? Which is more strongly supported?
Theories aim to provide explanations for observations (essentially to provide the “why”). Laws aim to provide descriptions of observed phenomenon (provide the “how”).
Both are EQUALLY supported by data and scientific tests
What is considered “not science”? Why? What violates scientific method?
Things aren’t scientific if they don’t adhere to the scientific method or peer review process. This doesn’t necessarily mean they’re wrong or unimportant, they’re just not science.
Things violate the scientific method if they don’t rely on repeated observation, can’t be tested (non-falsifiable hypotheses), and/or don’t accept falsification
Construct a hypothesis and null hypothesis
If I turn the key in the ignition, the car will start
If I turn the key in the ignition, nothing will happen
If I smack my head into this wall, it will hurt me.
If I smack my head into this wall, I won’t feel it.
How old is the universe and how do we know?
About 14 billion years old
The furthest light that we’ve observed in the universe is just under 14 billion lightyears away
How old is the Earth and how do we know?
About 4.6 billion years old
We know this based on geometric dating of the oldest rocks/grains within rocks, as well as testing on meteorites
What is the evidence that supports the Big Bang Theory?
Observation of light waves in the universe as red-tinted (which, according to the Doppler effect, means they’re moving away)
Background cosmic radiation (the observable “echo” that resulted from the initial explosion)
How does the Doppler effect work?
If a wave is moving towards you, the wavelength will appear to compress/shorten, causing it to appear blue (shorter wavelength of light)
If a wave is moving away from you, the wavelength will stretch and shift toward red light
In the universe, almost everything has a red tint, meaning it’s moving away from us
How did the moon form and how do we know?
The moon formed when a large planetesimal hit Earth, causing debris to be ejected into orbit
Earth’s gravitational field captured this debris and eventually, it clumped together and formed a sphere due to gravity
We know this because:
- Earth is slightly titled
- The mantle is smaller than expected based on other planets
- The moon has the same rocks and chemical makeup as the Earth’s mantle
How and where are elements formed? What about heavy elements?
After the Big Bang, nucleosynthesis led to the formation of hydrogen and helium (the simplest elements)
As stars burn off these elements, they collide with one another and combine to form new elements (up until Iron)
Heavy metals are created when stars explode in supernovas because this event releases a lot of energy and increases the chances of atoms hitting each other to form elements heavier than Iron
What is the Iron Catastrophe?
Once the Earth got big enough, it began to differentiate into layers based on density, giving us the Iron dense core, the mantle, and the crust
As the core formed and spun, it created Earth’s magnetic field, allowing the ozone layer to form
Where does our water come from? Our atmosphere?
At this time, Earth was mainly lava and volcanoes. At these eruption sites, gas is released (along with molten rock of course)
These gases, such as hydrogen, accumulate and are trapped by the ozone layer to form the atmosphere
One such gas was water vapor and this became the main source of water for the oceans
How are the layers of the Earth defined? What does density have to do with this?
The core, mantle, and crust have different chemical compositions based on density (the most dense elements clump to the core/center, with the mantle being made of heavy silicates)
How do we know about the layers of the Earth?
Seismic waves tell us what the core is made out of because there are different travel times as they move through different mediums
What are the 2 types of crust?
How are they different?
Continental - less dense + mainly granite
Oceanic - denser b/c it’s made out of basalt (iron and magnesium)
What are some lines of evidence for plate tectonics?
What about for continental drift?
C.D. = continents seem to fit together like puzzle pieces, matching fossil records, matching landforms like mountains, glacial rocks, continuity of fault lines
P.T. = all of this + seafloor spreading
What are the 3 types of plate boundaries?
What features are associated with each?
1) Divergent (apart) = continental rifting and ocean basins (+ mild earthquakes)
2) Convergent (together) = major earthquakes, volcanoes, and mountain ranges
3) Transform (side-by-side) = moderate earthquakes
What are the 3 types of Convergent plate boundaries?
1) Continental - Continental = no subduction (similar densities) = mountains
2) Oceanic - Oceanic = subduction of older plate (b/c older = colder)
3) Oceanic - Continental = subduction of oceanic b/c denser materials
How did paleomagnetism help explain seafloor spreading?
Rocks preserve magnetization when they cool and solidify (dip below the “Curie temperature”)
This means that when magnetic reversals occur (switching of the m. north and south poles), this is reflected in the rock formations
This led to the creation of magnetic stripes along the ocean floor where magma is released and forms new rocks
How does density play a role in plate tectonics/subduction?
When plates collide, the denser one will be pushed beneath the other and sink back into the Earth’s interior at a subduction zone
What stage of the Wilson cycle is the Atlantic Ocean in? The Pacific?
Atlantic = younger (juvenile) b/c it’s growing
Pacific = older (elderly) b/c it’s shrinking
Are the Himalayas still growing? Why/How?
Yes, because they are formed by a continental-continental convergent boundary, in which two plates of very similar densities collide and neither subducts
Can mountains form along Oceanic-Continental plate boundaries?
Yes, but they’re much smaller than C-C
Ex: the Andes
What are minerals made out of?
Elements, the smallest unit of which is atoms (composed of protons, neutrons, and electrons)
What are the types of bonds that hold minerals together?
Ionic - exchange of electrons, then held together by the attraction of a positive cation to a negative anion (ex: salt)
Covalent - sharing of electrons, leading to strong bonds and difficult to break materials (ex: diamond)
Metallic - electrons shared across the whole material (cations surrounded by moving cloud of electrons), leading to weak bonds but good conduction of electricity
What is the definition of a mineral?
A naturally occurring, inorganic, crystalline solid with a specific chemical formula
Where do most minerals/crystals form from? Liquid or solid?
Liquids (magma)
What is a polymorph? How do they change? How does this work in a real geologic setting?
Minerals with the same chemical formula but different structures
Each polymorph is formed under specific conditions - replicate those conditions and you can change a mineral into its polymorph (hypothetically)
Real ex: as oceanic crust is subducted under continental crust, it is put under intense heat and pressure, but these conditions are inconsistent across the entire subduction zone. This means polymorphs will form based on the conditions they’re in
What is a polymorph of diamond?
Graphite (NOT COAL, PLEASE DEAR GOD COAL IS NOT A MINERAL)
How does cleavage in minerals work?
It will break in a predictable pattern based on the location/direction of the weakest bonds
If it has equally strong bonds across the mineral, it will have fracture (irregular breakage), NOT cleavage (ex: quartz)
What is a rock?
One or more minerals
Can we tell where certain materials are formed? How?
Yes, based on their physical properties, particularly density (if it’s denser, we can assume it was made in the mantle or came from a meteorite)
Why do minerals have different levels of hardness?
Because of the different types of bonds (covalent bonds = stronger mineral)
What are some of the ways we ID minerals?
Cleavage - predictable breakage
Facture - unpredictable breakage
Luster - metallic or nah
Color - some are distinct
Streak - color of powdered form
Density - mass/volume
Crystal Form - geometric shape
Hardness - resistance to scratch
Some minerals don’t form in distinctive crystal forms because of…
Chemical impurities (which lead to variations)
Explain Bowen’s Reaction Series
Temperature impacts which minerals are formed, which means that minerals formed under different temps will never form in the same rock (though it may be possible for them to be found in the same sedimentary rock)
Why do we care about minerals? How do we use them?
Minerals are used in just about everything: jewelry, salty food, medications, powdered makeup, and technology (heavy metals, often those found in meteorites, are essential components of electronics)
What are the 3 types of rocks?
Igneous, Sedimentary, and Metamorphic
Where are igneous rocks sourced from?
When molten rock in the form of either lava (above the surface) or magma (below the surface) cools and crystallizes
How does cooling rate affect the look of igneous rocks?
Cools faster = smaller grains and smoother texture
Cools slower = bigger grains and rougher texture
What affects the cooling rate?
The location of the rock when it solidifies
Extrusive = above the surface
Intrusive = below the surface
Texture
The size, shape, and arrangement of the mineral grains inside of a rock (describes the rock’s overall appearance as either rough or smooth)
Aphanitic
Absence of visible crystals due to cooling so fast
Phaneritic
Visible crystals or mineral grains
Partial melting
Minerals have different chemical and physical properties, including different melting points
When there are several minerals inside a rock, they won’t melt at the same time
This means the rock with be partially melted and partially solid
Decompression melting
When pressure decreases, the melting point decreases (less heat is needed to make the rock melt)
This occurs at areas in which molten rock is rising towards the surface (top of convection cells, hot spots, and divergent plate boundaries)
Which has a higher melting point, the mantle or the continental crust?
The mantle b/c it’s lower in the Earth and subject to greater pressure
Pluton
A crystallized remnant (intrusive rock) of a magma chamber
Other intrusive rock formations:
- Sill (horizontal)
- Pipe (vertical)
- Dike (angled)
Chilled Margin
When magma touches existing rock, it melts the closest part, which then cools very quickly
This leads to a fine grained rim around an intrusive rock (where it came into contact with existing rock)
Inclusions
A piece of an existing rock breaks off into the magma and remains unmelted, becoming part of the final intrusive rock
What does Felsic and Mafic mean?
The classification of igneous rocks based on composition and silica content
Felsic = high silica (lighter color), low iron/magnesium, low water content (high viscosity + explosive), low melting point (crystallizes last)
Mafic = low silica (darker color), high iron/magnesium, high water content (low viscosity), high melting point (crystallizes first)
What are the other two classifications of igneous rocks besides mafic and felsic?
Intermediate - in the middle of literally everything
Ultramafic - mafic rock on steroids
What does Bowen’s reaction series tell us about the formation of igneous rocks?
Ultramafic rocks crystallize first because they have a high melting point
Felsic rocks crystallize last because they have a low melting point
Explain assimilation and fractional crystallization
Assimilation = existing rock gets melted into intruding magma and becomes a part of it
F.C. = change in the composition of magma as it cools (denser materials get “picked out” first)
Xenolith
A rock left intact from the assimilation process (wasn’t melted completely when it was taken up by the intruding magma)
How can fractional crystallization cause changes in overall chemistry over the life cycle of rocks?
Since the denser materials will be taken out over time, this means rocks gradually get less dense and more felsic
How does the understanding of igneous rocks predict volcanic activity?
Magma composition (based on our understanding of the minerals within the magma) affects volcanic eruptions. That is, lower viscosity magma flows more easily, while higher viscosity magma is more explosive
How do plate tectonics influence the igneous rocks we see?
The igneous rocks that form are based on the composition of the magma/lava, which differs depending on where the material melted (based on tectonic activity)
E.g. - magma that rises from the lower mantle will form (ultra)mafic rocks, magma that comes from the subduction of oceanic crust will form mafic rocks, and magma that results from the melting of continental crust will form felsic rocks
How can we determine how far away a clastic sedimentary rock is from its source?
Rounding and sorting
Explain the concepts of physical and chemical weathering. Can we predict what will weather first, and if so, how?
Physical - essentially rocks breaking down other rocks, with no chemical alteration (water, wind, ice)
Chemical - changes the chemical composition by reacting with water, oxygen, acid, etc.
Rocks that are lower on the hardness scale will weather first
What does grain size have to do with water energy?
The larger a grain is, the more energy or velocity is required to move it
Can you ID the basic types of sed rocks (sandstone, mudstone, etc.)
How do we base those classifications?
The classification of clastic sedimentary rocks is based on the sizes of the sediments and then by the roundness
How can igneous and metamorphic rocks become sedimentary?
Weathering and erosion (followed by either compression or cementation)
What is the difference between clastic and carbonate?
Clastic = made up of compacted sediments (physical)
Carbonate = made up of interlocking crystals (chemical)
Where are carbonate rocks typically found?
Near water or marine environments such as coral reefs
How do sea level rise and fall naturally?
Due to the melting and and freezing of glacial ice (usually in a predictable pattern)
Transgression v. Regression
Sea level rise v. Sea level fall
How are evaporites formed?
Salts left behind by the evaporation of seawater
What are the different sediment structures? How are they formed?
Beds - layers of sediment with distinct properties
Mudcracks - surface cracks that form when wet sediment (mud) is exposed to air and shrinks as it dries out
Ripple Marks - small curving ridges formed when fluid currents agitate the surface sediment (push it in the direction of the flow)
What does it mean if ripple marks are symmetrical? Asymmetrical?
Sym. = water flow goes back and forth (like the tides)
Asym. = water flows in one direction (like a river)
Cross Beds and Graded Beds
Cross = inclined layers caused by water/wind movement (tells us info about ancient currents)
Graded = coarse grains @ bottom, fine grain @ top
What is needed to make metamorphic rocks?
Heat, pressure, and/or fluid
What is a protolith? What is the most common one?
The original rock before metamorphism (mudstone is the most common)
How do metamorphic rocks link to plate tectonics?
Different plate boundaries will have varying degrees of heat and pressure, which will then lead to different grades of metamorphic rocks. Thus, observation of the rock can inform us about the type of boundary it may have formed at
What are some of the changes we see to rocks in metamorphic processes?
Recrystallization, Phase change, Metamorphic reactions, Pressure solution, Plastic deformation, and Foliation
Recrystallization
Heat = grains expand and fuse together (creating bigger grains with wonky boundaries)
Phase change vs Metamorphic reactions
P.C. = transformation of a mineral into one of its polymorphs (a physical change to crystal structure)
M.R. = a chemical change
Plastic Deformation vs Pressure Solution
P.D. = squishing spherical grains into an elliptical shape
P.S. = squishing spherical grains into elliptical ones, while also releasing the fluids inside of them (leading to wonky boundaries of crystallized fluid between grains)
Foliation
Minerals realigning into a preferred orientation (leading to a wave-like pattern)
Thus, Non-foliation = no preferred orientation and no wavy pattern
How can hydrothermal metamorphism happen?
Rocks come into contact with very hot water solutions, which speeds up metamorphic reactions and leads to compositional changes (called metasomatism)
What is the difference between stress and pressure?
Confining = pressure from all directions at once
Directed = pressure from a specific direction = bends/folds
(Shear) Stress = directed pressure acting in parallel but opposite directions
What are some signs of increasing metamorphism?
The grade of the rock depends on how different it looks from its protolith (more different = more metamorphosed)
Thermal/Contact Metamorphism
Magma comes into contact with a rock (ex: magma intrusions)
Dynamic Metamorphism
Shearing (or shear stress) that causes recrystallization and new textures (ex: a transform plate boundary)
Regional Metamorphism
A broad region of metamorphism caused by high pressure over a large area (ex: convergent plate boundary)
How do deep-formed metamorphic rocks get to the surface?
Exhuming: at a convergent plate boundary (mainly continental-continental), pressure will force things to go upwards
Explain the whole rock cycle (in simple terms)
MAGMA or lava (the starting point of all rocks) + cooling/crystallization = IGNEOUS
Weathering + erosion = sediments
Sediments + compaction + cementation = SEDIMENTARY
Heat + pressure + fluids = METAMORPHIC
Melting of any of the 3 types of rock = MAGMA once again
What is relative and absolute age dating/ Why do we use relative?
Relative = comparison
Absolute = actual age/exact #
It can be difficult to find the exact age of rocks, especially older ones, so we use relative dating in place of exact numbers
What are the principles of stratigraphy?
These principles help use compare layers of rock to discover the order of events (relative ages):
Superposition, Original Horizontality, Lateral Continuity, Cross-cutting Relationships, Principle of Inclusions, Faunal Succession
Superposition
The oldest rock layer will be at the bottom (if undisturbed)
Original Horizontality and Lateral Continuity
O.H. = rocks form in horizontal layers
L.C. = rock layers form in unbroken, flat expanses, so if something divides them (like a river), the division must have happened second
Cross-cutting Relationships
A geologic feature that cuts through another will be younger than the thing it cuts through
Principle of Inclusions
Clasts within a rock are older than the rock itself
Faunal Succession
Fossils contained in successive layers of rock occur in predictable orders and combinations
Normal vs Reserve Fault
N = hanging wall shifts down
R = hanging wall shifts up
How does Walther’s Law of Facies work? Are there times it doesn’t work?
We should be able to “read” the rock layers like a book (starting at the oldest at the bottom all the way to the top)
If there are rock layers (“chapters”) missing from the “book”, it can be difficult to study. These missing layers are known are unconformities
How does radiometric dating work? Why can’t we use carbon dating for very old things?
Unstable isotopes will naturally decay (from parent to daughter) at a constant rate called a half life. By measuring the amount of parent and daughter isotope, we can tell how old something is
Carbon is good for dating organic material, but not for very old things because it has a short half life
How did we make the geologic time scale?
Most of it was constructed with relative dating, especially biostratigraphy (using index fossils to measure a unit of time), with some absolute dates via magneto-stratigraphy, dendrochronology (studying tree rings), and radiometric dating
What is an index fossil? What characteristics do good ones have?
Specific fossils used to define units on the geologic scale
Must be: abundant, easily identifiable, geographically widespread, lived independent of environment, and lived for a narrow stratigraphic/temporal range
