Earth Science Reviewer – Core Vocabulary

Earth’s Internal Structure (C-M-O-I)

  • Crust
    • Outermost solid shell where all terrestrial life and human activities occur.
    • Composition: primarily silicate minerals (granite in continents, basalt in ocean floors).
    • Average thickness ≈ 35\,\text{km} (continental) and 5\,\text{km} (oceanic).
    • Practical importance: hosts mineral resources, groundwater reservoirs, and provides the tectonic “rafts” (plates) on which continents drift.
  • Mantle
    • Extends from base of crust to
      2\,900\,\text{km} deep.
    • Semi-solid but able to flow slowly; made mostly of peridotite (olivine + pyroxene).
    • Convection currents move heat from Earth’s interior, driving plate tectonics (volcanism, mountain building, earthquakes).
    • Philosophical insight: Illustrates that even apparently rigid rocks flow on geologic time-scales, challenging the lay concept of “solid ground.”
  • Outer Core
    • 2\,900\,\text{km}–5\,150\,\text{km} depth; liquid iron–nickel alloy.
    • Flowing metal generates Earth’s geomagnetic field through the dynamo effect, shielding biosphere from harmful solar wind and enabling navigation technologies (compasses, bird migration).
  • Inner Core
    • Radius ≈ 1\,220\,\text{km}.
    • Solid iron (with some nickel); temperature estimated near 5\,700\,^{\circ}\text{C}, yet kept solid by immense pressure (>330\,\text{GPa}).
    • Growth of inner core slowly releases latent heat, sustaining outer-core convection.
  • Seismic Waves
    • P-waves (compressional) travel through solids & liquids; S-waves (shear) stop in liquids, revealing liquid outer core.
    • Wave refraction/reflection maps boundaries (Moho, Gutenberg, Lehmann discontinuities).

Earth’s Subsystems (G-H-A-B)

  • Geosphere
    • All solid Earth materials (rocks, soils, plate tectonics).
    • Provides nutrients and habitat foundation for biosphere.
  • Hydrosphere
    • Total water in all phases: oceans (≈97\% of Earth’s water), rivers, groundwater, glaciers, atmospheric vapor.
    • Regulates climate via heat capacity and ocean currents.
  • Atmosphere
    • Gaseous envelope (~78\% \text{N}2, 21\% \text{O}2); controls weather, climate, and shields from UV (ozone layer).
    • Conduit for biogeochemical cycles (carbon, nitrogen).
  • Biosphere
    • All living organisms, from microbes to redwood forests.
    • Acts as a geochemical engine (e.g., photosynthesis lowers \text{CO}2, raises \text{O}2).
  • Sphere Interactions
    • Volcanic eruption (geosphere) emits ash/aerosols → alters atmospheric composition → affects photosynthesis & animal health (biosphere) → ash in clouds seeds precipitation, impacting hydrosphere.
    • Deforestation (biosphere-driven) exposes soil (geosphere), changes evapotranspiration (hydro + atmo), and influences regional climate (feedback loops & ethical land-use debates).

Major Geologic Processes

  • Weathering
    • Physical (freeze-thaw, thermal expansion) & chemical (hydrolysis, oxidation) breakdown of rock in situ.
    • Produces regolith, clays, and releases ions essential for soil fertility.
  • Erosion
    • Transport of weathered material by water, wind, ice, or gravity.
    • Rates accelerated by human activity (agriculture, mining) → soil loss = sustainability concern.
  • Sedimentation / Deposition
    • Settling of particles when transporting medium loses energy; forms strata that preserve fossils & climate records.
    • Over geologic time lithifies into sedimentary rock (compaction + cementation).
  • Mass Wasting
    • Downslope movement under gravity (landslides, rockfalls, mudflows).
    • Triggered by earthquakes, saturation, deforestation—vital for hazard planning.
  • Process Chain
    \text{Rain} \rightarrow \text{Weathering} \rightarrow \text{Erosion} \rightarrow \text{Deposition} \rightarrow \text{Sedimentary Rock}

Universe & Solar System Overview

  • Big Bang
    • Universe began 13.8\,\text{billion years} ago from a singularity: rapid expansion produced matter, energy, space, and time.
    • Key evidence: Cosmic Microwave Background (CMB) radiation at 2.7\,\text{K}; Hubble’s Law (galaxies receding proportionally to distance) → universe still expanding.
  • Solar Nebula Theory
    • Solar System formed 4.6\,\text{billion years} ago from rotating disk of gas & dust.
    • Gravity contracted most mass into proto-Sun; remaining material accreted into planets, moons, asteroids.
  • Planetary Differentiation
    • Temperature gradient: inner region hot → volatile elements vaporize → terrestrial (rocky) planets (Mercury, Venus, Earth, Mars).
    • Outer region cool → ices & gases retained → gas/ice giants (Jupiter, Saturn, Uranus, Neptune).
  • Lunar Formation (Giant Impact Hypothesis)
    • Mars-sized body (Theia) collided with early Earth; ejected debris re-accreted into Moon.
    • Explains identical oxygen isotopes & reduced lunar iron core.
  • Philosophical note: Our planet, moons, and even life itself originate from cosmic collisions and stellar processes—humans are literally “star stuff.”

Hydrologic (Water) Cycle

  • Evaporation
    • Solar energy converts liquid water to vapor (latent heat flux regulates climate).
    • Primary sources: oceans (≈86\% of global evaporation), lakes, vegetation (transpiration).
  • Condensation
    • Cooling air reaches saturation → vapor forms cloud droplets/ice crystals; releases latent heat powering storms.
  • Precipitation
    • Rain, snow, sleet, hail return water to surface; global mean ≈1\,000\,\text{mm yr}^{-1}.
  • Collection / Runoff / Infiltration
    • Water gathers in rivers, lakes, oceans; infiltrates to recharge aquifers; or glacially stored.
    • Imbalance in collection vs. evaporation drives sea-level rise.
  • Sphere Connections
    • Water cycle couples hydrosphere with atmosphere (clouds), geosphere (weathering & nutrient transport), and biosphere (plant uptake).
    • Ethical dimension: Freshwater scarcity highlights need for sustainable management.

Earth Science as an Integrated Discipline

  • Sub-fields: Geology, Oceanography, Meteorology, Astronomy.
  • Unifying theme: systems thinking—changes in one component ripple through others (e.g., climate change links atmospheric CO₂, ocean acidification, glacial melting, biodiversity loss).
  • Societal relevance: predicting natural hazards, locating resources, informing environmental policy.

Rock Types & Mineral Formation

  • Igneous Rocks
    • Form by solidification of magma/lava.
    • Intrusive (Plutonic): slow cooling → coarse grains (e.g., Granite: quartz + feldspar + mica).
    • Extrusive (Volcanic): rapid cooling → fine grains (e.g., Basalt: plagioclase + pyroxene).
    • Provide information on mantle composition & volcanic hazards.
  • Sedimentary Rocks
    • Form from lithified sediments or chemical precipitation.
    • Clastic (Sandstone: quartz grains) & Chemical/Biogenic (Limestone: calcite from shells).
    • Preserve fossils → paleo-environment reconstruction.
  • Metamorphic Rocks
    • Pre-existing rocks altered by heat, pressure, or fluids.
    • Examples: Marble (metamorphosed limestone, mainly calcite) & Slate (metamorphosed shale, exhibits foliation).
    • Useful for studying tectonic pressure-temperature paths and are valuable building stones.
  • Rock Cycle Summary
    \text{Magma} \xrightarrow[]{cool} \text{Igneous} \xrightarrow[]{weather\,\&\,erosion} \text{Sediments} \xrightarrow[]{lithify} \text{Sedimentary} \xrightarrow[]{heat\,pressure} \text{Metamorphic} \xrightarrow[]{melt} \text{Magma}
  • Minerals
    • Naturally occurring, crystalline substances with fixed chemical composition (e.g., quartz \text{SiO}2, calcite \text{CaCO}3).
    • Mineral assemblage reflects formation conditions—geothermobarometers in metamorphic studies.

Quick Enumeration & Concept-Map Reminders

  • Types of Igneous Rocks: Intrusive, Extrusive.
  • Types of Erosion: Water, Wind, Glacial.
  • Water Cycle (order): Evaporation → Condensation → Precipitation → Collection.
  • Concept Map for Rocks & Minerals should include:
    • Three rock classes ↔ two examples each ↔ associated minerals ↔ formation environment (heat, pressure, magma, ocean settings).
    • Use arrows to show transformations (e.g., shale → slate → schist).

Memory Aids & Study Tips

  • Acronyms
    • C-M-O-I (Crust, Mantle, Outer core, Inner core).
    • G-H-A-B (Geosphere, Hydrosphere, Atmosphere, Biosphere).
  • Visualization
    • Think of Earth layers as a four-layer cake (crust = icing).
    • Picture water cycle as a traveler moving through states of matter.
  • Active Learning
    • Draw mini diagrams, flow charts, concept maps.
    • Teach a peer: explaining solidifies understanding.
    • Relate concepts to local examples (hometown river erosion, local rock outcrops).
  • Ethical/Practical Connections
    • Deforestation, groundwater depletion, and climate change exemplify the real-world stakes of Earth Science knowledge.