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.