Earth Systems Science Unit 2 Review: Earth's Structure and Composition

Core Concepts

• Earth is a dynamic planet consists of various layers and structures
• Plate tectonics theory explains the movement and interaction of Earth's lithospheric plates
  • Driven by convection currents in the mantle
  • Causes earthquakes, volcanic eruptions, and mountain building (Himalayas)
• The rock cycle describes the continuous transformation of rocks between igneous, sedimentary, and metamorphic forms
• Earth's composition includes a solid inner core, liquid outer core, mantle, and crust
  • Crust and uppermost mantle form the lithosphere
• Geologic processes shape Earth's surface over time (weathering, erosion, deposition)
• Understanding Earth's structure and composition helps predict natural disasters and locate resources (oil, minerals)

Earth's Layers

• Crust: Outermost layer, varies in thickness (oceanic crust ~5-10 km, continental crust ~30-50 km)
  • Oceanic crust is denser and thinner than continental crust
• Mantle: Layer between crust and core, ~2,900 km thick
  • Upper mantle is solid, lower mantle is partially molten
  • Convection currents in the mantle drive plate tectonics
• Outer Core: Liquid layer, ~2,300 km thick, composed primarily of iron and nickel
  • Convection in the outer core generates Earth's magnetic field
• Inner Core: Solid layer, ~1,200 km thick, composed primarily of iron and nickel
  • Extremely high pressure causes the inner core to be solid despite high temperatures
• Lithosphere: Rigid outer layer, includes crust and uppermost mantle
• Asthenosphere: Partially molten layer beneath the lithosphere, allows lithospheric plates to move

Plate Tectonics

• Theory that explains the large-scale motion of Earth's lithosphere
• Lithosphere is divided into several plates that move relative to each other
• Plate boundaries: Divergent, convergent, and transform
  • Divergent boundaries: Plates move apart, creating new crust (mid-ocean ridges)
  • Convergent boundaries: Plates collide, causing subduction, mountain building, and volcanism (Andes Mountains)
  • Transform boundaries: Plates slide past each other, causing earthquakes (San Andreas Fault)
• Driving forces: Convection currents in the mantle, slab pull, and ridge push
• Evidence for plate tectonics: Seafloor spreading, magnetic anomalies, and fossil distributions
• Plate tectonics explains the formation and distribution of landforms, earthquakes, and volcanic activity

Rock Cycle and Types

• Rock cycle: Continuous process of rock formation and transformation
• Igneous rocks: Formed from the cooling and solidification of magma or lava
  • Intrusive (plutonic) rocks: Cool slowly beneath Earth's surface (granite)
  • Extrusive (volcanic) rocks: Cool rapidly on Earth's surface (basalt)
• Sedimentary rocks: Formed from the compaction and cementation of sediments
  • Clastic sedimentary rocks: Composed of rock fragments (sandstone, conglomerate)
  • Chemical sedimentary rocks: Formed by precipitation from solution (limestone, rock salt)
  • Organic sedimentary rocks: Formed from the remains of organisms (coal, chert)
• Metamorphic rocks: Formed from the transformation of existing rocks under heat and pressure
  • Foliated metamorphic rocks: Have a layered appearance (gneiss, schist)
  • Non-foliated metamorphic rocks: Do not have a layered appearance (marble, quartzite)

Earth's Composition

• Crust: Primarily composed of silicate minerals (feldspars, quartz)
  • Oceanic crust: Mafic composition (rich in magnesium and iron), denser than continental crust
  • Continental crust: Felsic composition (rich in silica and aluminum), less dense than oceanic crust
• Mantle: Primarily composed of silicate minerals (olivine, pyroxene)
  • Upper mantle: Solid, composed of peridotite
  • Lower mantle: Partially molten, composed of silicate minerals and iron
• Core: Primarily composed of iron and nickel
  • Outer core: Liquid, composed of iron and nickel
  • Inner core: Solid, composed of iron and nickel
• Elemental abundance: Oxygen (46.6%), silicon (27.7%), aluminum (8.1%), iron (5.0%), calcium (3.6%), and others
• Mineral composition varies with depth due to changes in pressure and temperature

Geologic Processes

• Weathering: Breakdown of rocks and minerals at Earth's surface
  • Physical weathering: Mechanical disintegration of rocks (frost wedging, exfoliation)
  • Chemical weathering: Alteration of rocks by chemical reactions (dissolution, oxidation)
• Erosion: Removal and transportation of weathered material by water, wind, ice, or gravity
  • Fluvial erosion: Erosion by running water (rivers, streams)
  • Glacial erosion: Erosion by glaciers and ice sheets (U-shaped valleys, cirques)
  • Aeolian erosion: Erosion by wind (desert landscapes, sand dunes)
• Deposition: Settling of transported sediments
  • Fluvial deposition: Deposition by running water (alluvial fans, deltas)
  • Glacial deposition: Deposition by glaciers and ice sheets (moraines, drumlins)
  • Aeolian deposition: Deposition by wind (loess, sand dunes)
• Mass wasting: Downslope movement of rock and soil under the influence of gravity (landslides, rockfalls)

Key Terms and Definitions

• Lithosphere: Rigid outer layer of Earth, including the crust and uppermost mantle
• Asthenosphere: Partially molten layer beneath the lithosphere, allowing for plate movement
• Plate boundaries: Zones where lithospheric plates interact (divergent, convergent, transform)
• Subduction: Process by which one plate descends beneath another at a convergent boundary
• Mid-ocean ridge: Underwater mountain range formed by divergent plate boundaries
• Fault: Fracture in Earth's crust along which movement has occurred
• Earthquake: Sudden release of energy in Earth's crust, causing seismic waves
• Volcano: Opening in Earth's surface through which magma, ash, and gases are expelled
• Magma: Molten rock beneath Earth's surface
• Lava: Molten rock that has been expelled onto Earth's surface
• Igneous rock: Rock formed from the cooling and solidification of magma or lava
• Sedimentary rock: Rock formed from the compaction and cementation of sediments
• Metamorphic rock: Rock formed from the transformation of existing rocks under heat and pressure

Real-World Applications

• Plate tectonics helps predict the location and frequency of earthquakes and volcanic eruptions
  • Seismic hazard maps guide building codes and emergency preparedness plans
• Understanding rock types and formations aids in the exploration and extraction of natural resources (oil, natural gas, minerals)
  • Sedimentary basins are often targeted for oil and gas exploration
• Geologic processes shape landscapes and influence land use planning
  • Floodplains, coastal areas, and hillslopes require special considerations for development
• Knowledge of Earth's composition and structure informs the study of other terrestrial planets (Mars, Venus)
• Geologic time scale provides a framework for understanding Earth's history and the evolution of life
  • Fossils and rock strata help reconstruct past environments and climates
• Geologic hazards (landslides, sinkholes) are assessed and mitigated based on an understanding of Earth's structure and processes
• Geothermal energy utilizes heat from Earth's interior for power generation (Iceland)