Geological and Environmental Sciences Exam Notes

Solar System Formation (Nebular Theory)

  • Nebula forms from hydrogen, helium, and heavier elements from stars.

  • Gravity pulls gas/dust inward, forming an accretionary disk.

  • Proto-Sun forms at the disk's center.

  • Dust concentrates in inner rings, ice in outer rings.

  • Fusion starts; the Sun ignites.

  • Dust and ice form planetesimals via collisions.

  • Planetesimals collide, forming a proto-Earth.

  • Gravity shapes proto-Earth into a sphere; core and mantle differentiate.

  • Protoplanet collision forms a debris ring.

  • The Moon forms from the ring.

  • Atmosphere develops from volcanic gases.

  • Oceans form from condensed moisture and comets.

Earth Formation

  • Protoplanetary disk.

  • Orbit clears.

  • Chunks collide into planetesimals.

  • Planetismals amalgamate, growing larger.

  • Irregular proto-Earth forms.

  • Interior heats, softens.

  • A Mars-sized protoplanet collides 4.5 billion years ago.

  • Debris forms a ring around Earth.

  • The moon forms and clears the debris orbit.

  • Gravity reshapes the moon into a sphere.

Early Earth

  • 4.54 Ga (billion years old).

  • Extremely hot with constant volcanic eruptions.

  • Volcanic gases form the early atmosphere (H2O, CO2, NH4, CH4).

  • Tons of asteroid/protoplanet impacts until ~3.85 Ga.

  • Surface melts and remelts.

  • Impact energy separates heavy and light elements, forming core, mantle, crust, hydrosphere, and atmosphere.

  • Water present by 3.85 Ga, potentially from comets, chemical reactions, or volcanoes.

  • Earth cools; water condenses, forming oceans.

  • CO2 dissolves into oceans, precipitates into solids, and is trapped in the crust.

  • Oceans full of dissolved iron (Fe).

Atmosphere

  • Early atmosphere: H2O, CO2, NH4, CH4; greenish and cloudy.

  • No free oxygen initially.

  • Outgassing from Earth’s interior.

  • Water condenses, forming oceans.

  • CO2 dissolves into oceans, becomes trapped in rocks in the crust.

  • Modern Atmosphere

    • Nitrogen (N2): 78.08%

    • Oxygen (O2) - 20.95%

    • CO2 - 0.04%

  • O2 entered the atmosphere after photosynthesis evolved (1.8 Ga), significant O2 by 600 Ma.

Radioactive Decay Law

  • dN/dt=−λNdN/dt = -\lambda N

  • λ\lambda = decay constant

  • Parent = radioactive isotope (e.g., 238U^{238}U)

  • Daughter = stable isotope (e.g., 206Pb^{206}Pb)

  • Earth's oldest materials dated to 4.54 billion years (4.54 Ga).

  • Earth's age is constrained by measuring both Earth rocks and meteorites.

Earth's Structure (Chemistry and Physics)

  • Driving principles: pressure, temperature, gravity.

  • Based on chemistry and physics.

  • Crust (least dense) - Solid.

  • Mantle (denser) - Solid/Plastic.

  • Outer Core (most dense) - Liquid.

  • Inner Core - Solid.

  • Common elements: C, N, Fe, Ni, Si, O, Mg, S, Al, H, Na, Ca, K.

  • Crust: Major O, Si; Minor Fe, Al, Ca, Mg, Na, K, S

  • Mantle: Major Mg, O, Si; Minor Ca, Fe, Al

  • Outer Core: Fe, Ni, Minor O, S

  • Inner Core: Fe, Ni

  • Atmosphere/Biosphere: Major N, O, C, H; Minor P, S

Earth's Interior - Seismic Waves

  • Earthquakes act like ultrasounds.

  • P-waves (primary, compression): fast, move through solids and liquids.

  • S-waves (secondary, shear): slower, move only through solids.

  • Reflection and refraction occur when passing through different densities.

  • Surface waves: Love (horizontal shearing) and Rayleigh (rolling).

Mohorovičić Discontinuity ("Moho")

  • Boundary between crust and mantle.

  • ~35 km below continents, ~7 km below ocean crust.

  • Defined by increased seismic wave velocity.

Earth's Layers

  • Crust: Rigid, variable thickness and composition, 0.1-1% of Earth’s radius.

  • Lithospheric Mantle: Rigid, olivine, pyroxene, garnet, 35-100km depth.

  • Upper Mantle: Rigid, low-velocity zone (1-6% melt). Minerals change to spinel+perovskite.

  • Lower Mantle: Solid, minerals change to periclase + perovskite, densely packed

  • Outer Core: Liquid, Fe + Ni alloy.

  • Inner Core: Solid, Fe + Ni alloy.

Significance of Liquid Outer Core

  • Liquid outer core + Earth's rotation = magnetic field due to rotating spiral currents.

  • Results: Compass points north, Earth protected from solar wind by the magnetosphere.

  • Protects satellites (GPS) and electric grid.

  • Van Allen Belts trap charged particles.

Continental Drift (Alfred Wegener)

  • Continents fit together like a jigsaw puzzle.

  • Similar rocks, geologic structures, and fossils across the Atlantic.

  • Hypothesis: Continents were joined in a supercontinent ("Urkontinent" or "Pangaea").

Evidence for Continental Drift

  • Fit of continents (modern coastlines).

  • Locations of past glaciers (Paleozoic Era Ice Age = 280-260 Ma).

  • Climate belts.

  • Fossil distribution.

  • Matching geologic units (Pre-Cambrian rocks in S. America and Africa, Appalachian Mountains).

Paleomagnetism

  • Magnetic field generated by convection in the outer core and can reverse.

  • Magnetic declination: Angle between magnetic north and geographic north.

  • Magnetic signal recorded in rocks (sediments and cooled lavas).

  • Paleopoles: Past positions of Earth’s magnetic poles.

  • Magnetic anomalies: Differences between expected and measured magnetic field strength.

Bathymetry

  • Study of underwater topography using SONAR.

Mid-Ocean Ridge (MOR)

  • Submarine mountain belt at divergent oceanic plate boundary.

Sea Floor Spreading

  • New crust forms at mid-ocean ridges; old crust consumed elsewhere.

  • Spreading Rate: Atlantic = 2 cm/year, Pacific = 10 cm/year

  • Evidence: Sediments get older and thicker away from ridge axis, oldest oceanic crust is ~200 Ma.

Continental and Oceanic Crust

  • Oceanic Crust

    • Thinner

    • Denser

    • Low silica content (SiO2SiO_2)

  • Continental Crust

    • Thicker

    • Less Dense

    • High silica content (SiO2SiO_2)

Plate Tectonics

  • Lithosphere floats on asthenosphere (Isostasy).

Plate Boundaries

  • Divergent: Plates move apart, creating new crust (e.g., mid-ocean ridges, continental rifting).

  • Convergent: Plates move toward each other, consuming crust (e.g., subduction zones, continent-continent collisions).

    • Oceanic/Oceanic: One subducts; older, colder, denser plate subducts.

    • Continental/Oceanic: Creates volcanic arc; subducted crust melts and makes new crust with volcanic range.

    • Continental/Continental: collide, creates mountain ranges like Appalachians.

  • Transform: Plates slide past each other horizontally.

Features of Convergent Plate Boundaries

  • Earthquakes: Wadati-Benioff Zone.

  • Accretionary Prism: Sediment and rock scraped off downgoing plate.

  • Basins: Back-arc and fore-arc.

  • Trench: Deep trough bordering volcanic arc.

Transform Boundaries

  • Plates slide past each other, horizontal motion.

  • Fracture zones: Narrow bands of vertical fractures.

Special Cases

  • Triple Junctions: Three plates intersect.

  • Hot Spots: Isolated volcanoes from mantle plumes.

Margins

  • Active: Coincides with plate boundary (e.g., Coast of California).

  • Passive: Does not coincide with plate boundary (e.g., East Coast of US).

Orogeny

  • Mountain building, uplift, and deformation.

Deformation

  • Brittle: Cracking and fracturing.

  • Plastic: Bending and flowing.

Geologic Structures

  • Folds: Bends or wrinkles in rock layers (anticlines, synclines, monoclines, domes, basins, plunging folds).

  • Joints: Natural cracks in rocks (columnar jointing).

  • Faults: Fractures where rocks slide past each other (dip-slip, strike-slip, oblique-slip).

  • Veins: Seams of minerals in open joints.

  • Shearing Stress: moves one part sideways past another part

  • Foliation: layering formed by mineral alignment or compositional banding in metamorphic rock, differential pressure + shear stress.

Mountain Building and Plate Tectonics

  • Subduction zones (oceanic-continental).

  • Continental collisions (continent-continent).

  • Continental rifting.

Geologic Maps and Cross Sections

  • Geologic Maps: Show rock unit distribution.

  • Cross Sections: Depict subsurface contacts.

  • Strike and Dip: Measurements used to create maps and cross-sections

PART 2: MINERALS, IGNEOUS, SEDIMENTARY & METAMORPHIC ROCKS

1. Minerals

Crystal lattice: ordered atomic structure → physical properties.

Silicate groups: isolated, chain, double chain, sheet, framework.

Variable composition: solid solution series (e.g., olivine).

Mineral growth: from cooling magma, evaporation, hydrothermal activity.

Human uses: electronics (quartz), construction (calcite), pigments.

2. Igneous Rocks

Partial melting: source rock determines melt chemistry.

Fractional crystallization: mafic minerals crystallize first.

Assimilation: surrounding rock melts into magma.

Mafic lava = low viscosity (flows easily), Felsic lava = explosive.

Intrusions:

Dike: vertical.

Sill: horizontal.

Laccolith: dome-shaped.

Batholith: large, deep-rooted (e.g., Sierra Nevada).

3. Volcanism

Effusive eruptions: basaltic, low gas.

Explosive eruptions: rhyolitic, gas-rich.

Hazards: ashfall, pyroclastic flows, lahar (mudflows), gas release.

Monitoring: seismicity, gas emissions, ground deformation.

4. Sedimentary Rocks

Texture reflects transport history: well-sorted & rounded = long transport.

Lithification: compaction + cementation.

Environments:

Terrestrial: alluvial fans, rivers, deserts, lakes.

Coastal: beaches, deltas.

Marine: continental shelf, reef, deep sea.

Biochemical indicators: fossil types, shell composition.

Evaporites: form in restricted basins (e.g., halite, gypsum).

5. Metamorphic Rocks

Grades:

Low: slate, phyllite.

Medium: schist.

High: gneiss, migmatite.

Facies: mineral assemblages reflecting T/P conditions.

Tectonic settings:

Subduction zones: blueschist.

Continental collisions: high-grade regional.

Shock metamorphism: impacts (e.g., meteor craters).

PART 3: RESOURCES, GEOLOGIC TIME & RADIOACTIVE DATING

1. Energy Resources

Fossil fuels: formed in anoxic environments, buried over geologic time.

Coal: from terrestrial plant matter in swamps.

Oil: marine plankton → kerogen → crude oil.

Gas hydrates: methane in ice lattices under deep-sea sediments.

Renewable energy: solar, wind, hydro, geothermal.

Environmental effects: greenhouse gases, acid rain, habitat destruction.

2. Mineral Resources

Strategic minerals: essential for technology (REEs, lithium).

Ore enrichment:

Mechanical: panning, sluicing.

Chemical: smelting, leaching.

Sustainability: recycling, reducing use, finding alternatives.

Reclamation: restoring land after mining.

3. Geologic Time

Time units:

Eon: Phanerozoic (visible life).

Era: Paleozoic, Mesozoic, Cenozoic.

Period: Jurassic, Cretaceous, etc.

Major events:

Cambrian Explosion (~541 Ma): rise in diversity.

Permian Extinction (~252 Ma): largest mass extinction.

K-T Boundary (~66 Ma): dinosaur extinction.

Quaternary (~2.6 Ma–now): ice ages, humans.

4. Radiometric Dating

Decay chains: multiple steps from parent to stable daughter.

Closure temperature: below this, radiometric clock starts.

Concordia diagram: used in U-Pb dating to check reliability.

Dating techniques:

Fission track: tracks from spontaneous nuclear decay.

Luminescence: trapped electron release dates last exposure.

Applications: archaeology, climate change, plate motion studies.