Exogenic Processes in Earth Science

Exogenic processes

• Erosion: process of soil and rock transportation
• Deposition: laying down of sediments transported by erosion agents
• Weathering: decomposition of rocks and materials on Earth's surface
  • Mechanical Weathering: rock breaks without chemical composition change
    • Temperature: repeated heating and cooling cause exfoliation (surface peeling)
    • Frost Action: water expands when frozen, breaking rocks
    • Abrasion: solid particles carried by wind, water, etc. wear down rocks
    • Living Organisms: plants, animals, and humans contribute to mechanical weathering
  • Chemical Weathering: change in rock's chemical composition
    • Hydrolysis (water): dominant factor in chemical weathering
    • Oxidation (oxygen): combines with substances to form new ones
    • Carbonation (carbon dioxide): combines with rainwater to form weak carbonic acid
    • Acidification (acid rain): organisms like plants produce acid, causing weathering.
  • Residual Soil: remains on its parent rock
  • Transported Soil: moved by wind, water, glaciers, and waves
  • Bedrock: parent rock under residual and transported soil.

Agents of Erosion

• Wind: active in deserts, fields, and beaches
  • Dunes: wind-built mounds of loose sand
  • Loess: fine sand and silt deposit from wind
• Running Water: major erosion agent (rivers, streams, runoff)
  • Runoff: rainwater flowing on the surface and into rivers/streams
  • Oxbow Lake: U-shaped water body formed when a river changes course

Plate Tectonics

• Seafloor Spreading:
  • New crust forms from intruding magma as plates move apart (lava erupts)
  • "Hot and less dense material from the mantle rises to the surface along mid-ocean ridges, pushing the seafloor away in both directions"
  • As oceanic crust moves away from ridges, it cools, contracts, and becomes denser, aiding ridge formation
  • Continuous magma formation causes ocean floor widening
  • Convection Currents: drive magma upwelling

Ocean Basin

• Evolution of Ocean Basin:

  • Embryonic Stage: continents separate forming rift valleys (e.g., Great Rift Valley)
  • Juvenile Stage: seafloor basalts form as continental margins separate, rift valleys deepen and flood

• Structure of Ocean Basin:

  • Continental Shelf: submerged part of continental landmass

Mass Movement Processes (downward movement of soil and rock under gravity)

• Slope Failure: caused by the weakening of supporting rocks by heavy rain
  • Alluvial Fan: fan-shaped deposit of sediments at the base of a stream
  • Delta: landform formed by sediment deposition at river mouths
  • Flood Plain: flat area near a river/stream
  • Levee: natural wall built by sediment deposits blocking water
  • Mudflow: rapid flow of water-saturated soil down a slope
  • Slump: downward sliding of rock/unconsolidated material on a curved surface
  • Debris Flow: soil and water flow down a slope
  • Creep: slow, gradual downhill movement of soil due to expansion and contraction

Folding (rock bending)

• Anticline: upward bend
• Syncline: downward bend
• Plateau: formed by folding

Faulting (rock fracture)

• Fault: rock movement along a fracture
• Normal Fault: rock on one side is lower relative to the other (tension)
  • Fault-block mountains: uplifted blocks of rock by normal faults
• Reverse Fault: one block pushed up relative to the other (compression)
• Strike-Slip Fault: sideways movement of blocks

Continental Drift Theory

• Alfred Wegener: proposed the theory of continental movement
• Pangaea: supercontinent
• Laurasia and Gondwanaland: continents that formed from Pangaea breakup

Geological Time Periods:

• Paleozoic Era (541 - 252 million years ago)

  • **Cambrian Period (541-485): ** Cambrian explosion of life, trilobites, the first vertebrates
  • Ordovician Period (485-444): diversification of marine life, first land plants
  • Silurian Period (444-419): early jawed fish, emergence of terrestrial ecosystems
  • Devonian Period (419-359): age of fishes, first tetrapods, mass extinction
  • Carboniferous Period (359-299): high oxygen levels, vast forests, first reptiles
  • Permian Period (299-252): rise of reptiles, dominant amphibians, largest mass extinction

• Mesozoic Era (252-66 million years ago)

  • Triassic Period (252-201): first dinosaurs, gymnosperms, mass extinction (end-Triassic)
  • Jurassic Period (201-145): dinosaurs, birds, flowering plants, giant-lizard hipped dinosaurs
  • Cretaceous Period (145-66): separation of Gondwana and Laurasia, emergence of flowering plants, placental mammals, mass extinction (dinosaur extinction)