Earth & Planetary Science

hypothesis vs. theory

testable possible idea for observed data vs. considered true through repeated testing… ethics include acknowledging others’ work/never falsify/teach others

early western european way of thinking

geocentric model (copernicus), then kepler’s laws of planetary motion (elliptical orbits/planet covers same amount of space over time no matter where in orbit/orbital period is proportional to its orbit size), newton’s law of conservation of angular momentum, john adams predicted existence unknown planet (neptune)

uniformitarianism & geoscientist way of thinking

james hutton idea that processes today operated in past, think in terms of hundreds of millions of years

Nucleosynthesis (creation protos & neutrons)

primordial (1000 seconds after big bang, H & He), stellar (fusion in stars, up to Fe^56), hydrogen/carbon/silicon burning (H+H=2^D, +H=3^He) aka fusion, spallation (cosmic radiation)

Evidence for Formation of Solar System

On light spectrum no radiation shines through at specific wavelength which tells you composition of photosphere (from gamma to shortwave it goes Ca - H - Fe - Mg - Na - O), or meteorites either primitive (unchanged since beginning time) or processed (new) or iron (core of something larger) & gives info composition

Nebular Hypothesis

spherical cloud gets perturbed and rotates then collapses into protoplanetary flat disk, where planetary evolution is not uniform: hottest at center Fe/Ni/Si first then frost line and H2O/Ch4/NH3

Planetary Evolution

Nuclear accretion and condensation where those w/ highest melting points condense first (creates frost line - idea water degassed from meteors on Earth, or Jupiter much closer slingshot in than out and pulled Gas Giants w/ it but mixed water w/ rocky planets first)

Earth’s Moon

Unusually large, large body hit earth & cores merged (our core lot iron moon’s little) then debris consolidated as moon, created 23 degree axis, other ideas: capture/co-accretion/excessive angular momentum & stuff sucked out to slow

Earth’s Structure

slightly elliptical, started as amalgamation materials then heat from collisions/radioactive decay created gravitational differentiation, 90% Earth = O/Mg/Si/Fe (O & Fe most abundant, then there’s lots Al/Ni/Ca/S)

Inner Core

solid, iron-nickel alloy, up to 1220 km, creates magnetic field through crystallization of outer core which releases heat of fusion, high pressure stabilizes iron (which is heavy so sinks)

Outer Core

liquid, iron-nickel alloy, up to 2260 km

Mantle

MOSTLY SOLID, SiO4, up to 2900 km, flows in the way glaciers flow, continents sit on top, also contains O/Mg/Ge, driven by conduction at top and bottom of mantle and convection in rest (flowing faster than conductive rate allows stay unmixed w/ core)

Crust

solid, mostly SiO4, 6-40 km, bimodal topography, also O/Ca/Si/Mg/N, lithosphere divided into mobile plate tectonics driven by mantle convection

Rayleigh Number

whether something convects or not: Temperature\*Depth\*Thermal Expansion\*Gravity\*Density / Viscosity\*Thermal Conductivity, >1000 = likely convect bc takes too long to conduct, temperature increases w/ depth… more likely to convect when inc temp gradient/dec viscosity/inc height/dec thermal conductivity/inc gravity

Convergent Plate Boundaries

Plates collide: Ocean-Ocean one bends and subducts creates trench, Ocean-Continental ocean plate will always subduct creates island arc, Continent-Continent resist subduction and bend up creates mountains

Divergent Plate Boundaries

Plates separate, forms gap that mantle fills forming new oceanic crust at mid-ocean ridges and rift valleys

Transform Plate Boundaries

Plates slide past each other, creates fracture zones and faults

Plate Tectonic Theory

Alfred Wegener proposed continental drift where continents drive through oceanic (false), based on jigsaw arrangement/matching continental shelf and fossil records/glacial deposits where shouldn’t be

Mid-Ocean Ridges

Harry Hess used sonar in WWII to study mid-ocean ridges - youngest along center and oldest along symmetrical exterior, igneous rocks point North and switch as poles reverse - magnetic isochrons of ridges form symmetric barcode

Drivers of Tectonic Activity

Convection coupling oceanic crust and moving w/ friction, gravity on peak of mid-ocean ridge creating ridge push, momentum of dense subducting oceanic plate creating slab pull

Mineral

Naturally occurring, solid, generally inorganic (can be biogenic), specific atomic arrangement of 3D periodic form , >4000 known

Polymorphs

Same chemical composition but diff minerals based on phase transitions, where form diff bonds (into triangular/tetrahedral/octahedra/dodecahedral w/ small cations filling in linked anions)

Structures of Silica (tetrahedrals)

Isolated tetrahedra (singular pyramid), single chain silicates (sharing corners), double chain silicates (think jewish star or double helix), sheet silicates (layer then cations then layer), framework (interconnected silicates - all O’s are shared)

Goldschmidt’s Rule of Substitution

minerals are rarely pure bc nature tends towards entropy, when atomic radii are similar (size difference within 15% and charge difference within +-1) atoms of different elements are likely to substitute for each other in a substance, eg. olivine can either be created by Fe or Mg and still be olivine but melting points often change

Formation of Crystals

Either from nucleation (from melt after melting temp lowered) or precipitation (saturated solution evaporates and crystals plop out), slow cooling/lots of space = large crystals, fast cooling/limited space = small crystals, Gibb’s Phase Rule: the more components there are in a system the more phase changes there are

Silicates

90% of crust, SiO4 tetrahedra, isolated = olivine, single chain = pyroxene, double chain = amphiboles, sheet silicates = micas/clay, framework = quartz/feldspar

Oxides

O2- bonds to cations, ore and gemstones, eg. add graphite which has carbon and is reductant that de-oxidizes hematite Fe2O3 to get pure iron

Carbonates

CO3^2-, triangular structure, eg. calcite and dolomite

Halides

evaporative deposits from salt precipitating out of sea water, eg salt flats

Sulfates

SO4^2- tetrahedra, evaporites, eg. gypsum and anhydrite

Sulfides

sed environments, hydrothermal, anaerobically formed, metallic and opaque, copper/zinc/lead/Hg/Co ores, eg. galena

Phosphates

PO4^3- phosphate ions, anisotropic structure (diff directions based on angle you’re looking)

Color

Caused by trace impurities, not diagnostic

Streak

Rub against porcelain tile, diagnostic, eg. hematite black but streaks red

Luster

Subjective way reflects light, metallic or nonmetallic (vitreous/resinous/waxy/earthy/pearly/silky)

Cleavage

tendency to break along certain weak points, number planes/angle cleavage, poor/good/perfect, eg. halite/galena/calcite have 3 planes & mica has one perfect plane

Fracture

not good cleavage so conchoidal breakage, in stronger framework bonds eg. quartz/obsidian (glass not mineral)

Moh’s Hardness Scale

rub rocks against each other and the harder will scratch the softer, talc is one and diamond is ten

Additional mineral tests

specific gravity (density), crystal habit, acid tests (halite bubbles in H2O and calcite bubbles in HCL), combustion (sulfur burns), magnetism, taste, smell

Rocks & Rock Cycle

Naturally occurring aggregates of mineral or nonmineral matter; wilson cycle of rift to mid ocean ridge and plate moves until subducted and brings another continent w/ it crashes to form mountains then rifts, pangea 237 million years old and rodinia 750 million years old

Igneous Rocks

Solidification and crystallization through cooling magma, starting point of all rocks, either fine grained from lava (extrusive) or coarse grained from magma (intrusive), most felsic to mafic: quartz/feldspar/mica/pyroxene/amphibole/olivine

Plutonic Rocks

Intrusive igneous, granite - diorite - gabbro - peridotite

Goldschmidt’s Rule on Differentiation

Elements have an affinity to substitute into groups: lithophiles like to go in silicates (continental crust), chalcophiles like to go in sulfides (oceanic crust), siderophiles like to go in iron (core), atmophiles like to go in atmosphere

Incompatible Elements

As melted mantle buoys up and solidifies the things that are incompatible in the mantle want to join melt (minerals that live in crust - K/Ca/Ba/Ur) and compatible things like to stay behind in mantle (Mg/Ni/Cr/Fe/Co/Zn), more compatible means mineral has smaller cations to fill in spaces in lattice of other mineral

Felsic vs. Mafic

Silica and Feldspar, less dense, lighter color, forms near surface, more viscous (extrusive rhyolite and intrusive granite) vs. Mg and Fe, more dense, darker color, forms deeper, less viscous (extrusive basalt and intrusive gabbro)

Pyroclasts

rocks cooled from violent lava explosions from pressure building in volcanic system of viscous felsic rock

Porphyry

rock w/ two distinct crystal sizes, phenocrysts grow large and slow then remaining melt rapidly cools around it

Solidus vs. Liquidus

Fully crystallized starts to convert to liquid vs. Increased conversion to liquid once only initial amount is still crystallized

Melting through Depressurization

If rock in the mantle moves up fast enough it’ll depressurize and turn adiabatic (doesn’t lose heat to surroundings) and ejects from geotherm (slope of temperature as a function of pressure) until it intersects w/ the solidus (similar slope but higher intercept at T) & rock has reached T sufficient to begin melting… mid ocean ridges and hot spots

Melting through Changing the Solidus

You either have a wet or dry solidus: if add water through subduction the geotherm doesn’t change but the melting point is lowered and you can cross solidus … island arc

Melting through Heating

Very rare, add heat and magma will melt, can occur by substituting elements changing properties of mineral… hot spot volcanism

Bowen’s Reaction Series (& Fractional Crystallization)

Minerals precipitate in order as a function of T and chemical composition of melt as magma chamber is cooled from 1200 to 600 degrees, ultramafic (w/ more density & higher melting point) precipitates first and felsic last (less dense & lower melting point)… olivine - pyroxene - amphibole - biotite mica - orthoclase feldspar - muscovite mica - quartz (after Mg and Fe precipitate out you’re left w/ mainly siliceous material until pure SiO2)… FC = crystals form & settle on magma floor in horizontal layers

Assimilation

Continuous partial melting mixes w/ parent rock to make new composition, xenoliths (extensions of one magma chamber) can reach into another chamber and combine w/ the differentiated rock

Forms of Magmatic Intrusion

Crystallized remnants of the last magma to move through rock: batholith (large intrusion magma) plutons (smaller intrusions) dikes (vertical extensions cross cutting rock) sills (horizontal extensions parallel to rock) stock (larger than dike moves to surface)

Oceanic Layers (bottom to top)

Magma, Peridotites (olivine/pyroxene rich rocks), Gabbros (basalts), sheeted dikes, pillow basalts, sediment, black smokers (fracture where water mixes & releases anoxic nutrients)

Sedimentary Rocks

Provides records past surface conditions, weathering breaks down igneous, erosion transports sed to deposition sites, burial compresses and lithification binds

Clastic Particles

Siliceous sediments, properties determined by current strength and distance of transport: rounding (angular vs rounded) and sorting (poor vs good), paleoflow directions - sed align in flow of river

Diagnostic Features of Sediments

Coarse Grains (>2 mm - boulder/cobble/pebble - sandstone/conglomerate), Medium Grained (.62-2mm - sand), Fine Grained (.039-.62mm - mud/silt), Ultrafine Grained (

Rift Basins

Tectonic plates separate, buoyant mantle rises and inflates top of ridge, increasing tension till the sides break apart and spread, creating basins on either side where deposition, eg. Red Sea

Thermal Subsidence Basins

As rift continues to spread, crust cools and contracts, creating depression and a passive margin, high dip angle in crust, eg. coral reefs in carbonate basins

Flexural Basins

Forearc basin created over subduction zone: as slab goes under it pulls a bit of above crust down before forming arc so there’s wedges on either side

Continental Sedimentary Environments

Lakes provide evaporites (halites/borate/nitrates/carbonate), or vegetation in swamps create peat

Sedimentary Structures

Mud (desiccation cracks when dried), cross bedding (laminations in terminating layers, saltation piles sed then falls downslope deposits on another dune, asymmetric when water unidirectional and symmetric when flow back and forth), bioturbation (organisms burrowing and turbate sed)

Composition of Sedimentary Rock Formations

Tillite (giant crystals surrounded by fine ones - glaciers slide rocks over another), Dropstones (glaciers dragging rocks over ocean and drop when melt), Turbidites (turbidity currents scour base and get massive granules that deposit out)

Creation of Sedimentary Rock

Burial layers sed and preserves through squeezing water out, diagenesis is chemical cementation (lithification) - precipitation of new minerals between sed to glue them together

Classification of Siliciclastic Sediments

75% siltstone/mudstone/clay, 14% carbonate, 11% sandstone/conglomerate; quartz arenite (everything else weathered away until almost completely quartz), bioclastic (limestone - calcite and aragonite, CaCO3, or phosphorite), evaporite halites (net evaporation > net precipitation)

Chert

Biogenic silica, SiO2, formed from shells of diatom and radiolarian, rainwater brings silica in, when photosynthetic algae die they fall and precipitate silica

What Controls Weathering Rates

surface area of grind (higher = faster - increases sites for water to interact w/ particles, want finer grains), temperature (hotter = faster - vibration provides more energy to overcome activation energy for chem reactions), amount of water (little = concentrated, a lot = diluted)

Congruous Weathering

Solutes released is equal to what’s dissolved (chemicals and charges balanced), eg. CaCO3 (calcium carbonate) + CO2 + H2O = Ca2 + 2H2CO3- … carbonate dissolves to neutralize acidity of CO2

Incongruous Weathering

Solutes released is not equal to what’s dissolved, eg. carbon sequestration: potassium feldspar + carbonic acid + water = kaolinite + silica + potassium + calcium bicarbonate (2KAlSi3O8 + 2H2CO3 + H2O = Al2Si2O5OH4 + 3SiO2 + 2K+ + 2HCO3-) where H+ is extracted and swapped w/ K+ to neutralize solution

Faint Young Sun Paradox; Solar Luminosity

solar luminosity has increased by 30% since beginning of earth (our rocks are 4 billion years old yet logically would’ve only crosses freezing point 2 billion years ago)

Urey’s Reaction

Net reaction: CO2 + CaSiO3 = CaCO3 + SiO2 … by adding carbonic acid to a pyroxene we have dissolved bicarbonate but not neutralized it, so we depolymerize the silicic acid to become quartz and water, allowing the calcium to react with the bicarbonate creating calcium carbonate and CO2 which gts sucked into limestone

Silicate Weathering Feedback

Negative Feedback Loop: Volcanism increases CO2 increases temperature, which increases weathering which sucks down more CO2 and decreases temperature - runaway GHG effect bc even if weathering sucks out all CO2 it means ocean temp still rising creating more water vapor increasing heat

Stability of Mineral Weathering

Inverse of bowens: what precipitates first is most unstable and dissolves first (bc conditions of creation farthest from conditions of Earth’s surface)… olivine - pyroxene - amphiboles - biotite mica - potassium feldspar - muscovite mica - quartz… felsic less likely dissolve and mafic more likely

Physical Weathering (& biological)

Better w/ colder temp: frost wedging (freeze and thaw), exfoliation (uplift decreases pressure so start breaking apart), salt weathering (halite precipitation wedges apart rock), spheroidal weathering (corners preferentially attacked by water), roots break up soil and extract CO2 which increases dissolution

Flux

Amount of water flowing along surface area per unit time… start at concentration of saturation (equilibrium w/ the solute) where rate of dissolution is greater than water transit time, but as increase transit rate mineral get dissolved less until so fast none weathers

Soils

Bottom bedrock constantly uplifted to create new soil, less weathering w/ thicker soil, at low erosion rates chemical weathering is low and same at high rates (bc no more material to weather) and highest in middle (parabola)

Metamorphic Rocks

Changes in pressure, heat, and chemical environments alter mineral compositions of existing rocks, studied to connect history of interior and exterior of earth, create centers of continents (ancient centers = cratons, oldest rock in middle younger surrounding)

Low and High Grade Metamorphism

Low grade = less T/P, high grade = more T/P, high grade = increased crystal size and coarseness of foliation… same parent rock but diff grade or diff parent but same grade all give diff types metamorphic rocks

Foliated Metamorphic Rock

Regionally metamorphosed, flat/wavy parallel cleavage lines preferred orientation… from low to high grade: slate - phyllite - schist - gneiss - migmatite

Nonfoliated Metamorphic Rock

Contact metamorphism, many equant crystals, granoblastics: hornfel/quartzite/marble/greenstones/amphibolites/granulite

Burial Metamorphism

A form of diagenesis, low grade from increasing pressure of sediments

Contact Metamorphism

Big source superheats rocks but low pressure, heat from igneous metamorphoses rock immediately surrounding

Regional Metamorphism

High pressure and temperature over widespread crustal area, common in subduction zones and convergent plates

Seafloor Metamorphism

Water infiltrates mid-ocean ridges and convects through basaltic lava

Other forms of metamorphism

Ultra high pressure (very low depth, rarely come to surface, creates mafic eclogites), shock metamorphism (shockwaves from meteor collision rapidly increase T/P, produce tektites)

Geochronology

studying naturally occurring clocks using either absolute aging (radioactive decay) or relative aging (stratigaphic record of rock sequences in relation to each other)

Steno’s Laws

Form of relative aging: Law of original horizontality (depositional centers always lay sediments horizontally), Superposition (oldest rock on bottom youngest on top), Lateral Continuity (sediments extend outward on a plane)

Cross-Cutting Relations

Form of relative aging, compressive forces act on horizontal layers to fold them into a bend, then top gets eroded, then new horizontal deposition cements the original layer at an angle

Faunal Succession

Form of relative aging, fossils succeed each other vertically in chronological order, rely on common organisms w/ shells (calcite) bc easier to preserve

Unconformities

Space in rock record bc not all preserved, from sedimentary rock being uplifted above sea level and eroded then sea level rises above it and deposition restarts

Disconformity

Flat layer, then erosive undulating layer (from uplift folding rock), then another flat layer, indicates missing time

Angular Unconformity

Tilted sedimentary layers then a cross-cutting layer, indicates both tectonic process and erosion in two time frames

Nonconformity

Igneous or metamorphic rock layer, then erosive undulating layer, then sedimentary layer, indicates shift in rock formation process

Divisions of Geologic Time

Era (paleozoic/mesozoic/cenozoic), period (cambrian, triassic, paleogene), epoch (period of time in life of species formation)