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Geology & Plate Tectonics Timeline – Essential Points

Early Observations of Earth

  • 1598 Ortelius publishes first modern atlas; notes Africa–South America fit ➔ early continental‐fit idea.
  • 1678 Hennepin documents Niagara Falls; recession rate (≈1 m/yr) implies Earth’s age ≫ biblical estimates (≥5{,}000 yrs).

Concept of Deep Time

  • 1795 James Hutton: rock cycle & uniformitarianism (“present is key to past”); Earth with “no vestige of a beginning nor prospect of an end.”
  • 1862 Lord Kelvin models Earth cooling ⇒ age ≈100 Myr; underestimated (ignored radioactivity).

Seismology & Earth’s Interior

  • 1846 Robert Mallet coins “seismic,” “epicentre”; shows quakes = crustal faulting, wave energy.
  • 1906 Oldham uses seismic‐wave refraction ⇒ liquid outer core; seismograph networks grow.

Fossil, Paleontological & Magnetic Evidence

  • 1858 Snider-Pellegrini: matching plant fossils across oceans ⇒ pre‐split supercontinent.
  • 1906 Bruhnes discovers remanent magnetism; finds polarity reversals (every 2\times10^{5}–10^{6} yrs).

Radiometric Dating & Nuclear Heat

  • 1905 Rutherford: nuclear decay, half‐life concept, internal heat source.
  • 1911 Arthur Holmes pioneers U–Pb dating; establishes quantitative geologic timescale (multiple isotope pairs, e.g., ^{238}\text{U}\rightarrow{}^{206}\text{Pb}).

Early Continental-Motion Hypotheses

  • 1910 F.B. Taylor links mountain belts to lateral continental drift; notes trenches = subduction zones (mechanism unresolved).
  • 1912 Alfred Wegener proposes “Continental Drift,” supercontinent Pangea; lacks driving force.
  • 1928 Arthur Holmes: mantle convection as drift mechanism; revises Earth age to ≈1.6 Gyr.

Ocean Floor Revelation

  • 1872–1876 HMS Challenger maps Mid-Atlantic Ridge; identifies deeps & highs.
  • 1895 Murray’s bathymetric charts prove seafloor relief.
  • 1939 WWII sonar maps guyots/seamounts (Hess).
  • 1959 Tharp–Heezen physiographic maps detail ridges & fracture zones.

Seafloor Spreading & Magnetic Stripes

  • 1955 Benioff detects dipping quake planes (now “subduction zones”).
  • 1961 Hess & Dietz: seafloor spreading—new crust at mid-ocean ridges.
  • 1963 Tuzo Wilson: mantle hotspots explain volcanic chains & guyot tracks.
  • 1965 Vine–Matthews–Morley: symmetrical magnetic stripes parallel ridges confirm spreading; age increases away from ridge.
  • 1965 Bullard uses computers to statistically fit South America–Africa on a sphere.

Plate‐Boundary Types & Wilson Cycle

  • 1965 Tuzo Wilson defines transform faults (e.g., San Andreas) connecting spreading centres & trenches.
  • 1966 Wilson Cycle: opening–closing oceans, supercontinent assembly/dispersal via subduction & spreading.

Modern Geodetic Measurement

  • 1950s–1960s WWSSN enhances global quake detection; quakes align with plate boundaries.
  • 1965 National Geodetic Satellite Program; Satellite Laser Ranging (SLR) network (accuracy ≈\pm1 cm).
  • 1976 Launch of LAGEOS satellites for high-precision crustal motion.
  • 1978 GPS constellation initiated; civilian use from 1993 (standard accuracy meters; geodetic receivers millimetres).
  • 1985 NASA SLR & GPS directly measure plate velocities (cm/yr), matching plate-tectonic predictions.