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Siccar Point, Scotland. The unconformable contact of Old Red Sandstone on vertical Silurian rocks noted by James Hutton, who in 1788 first recognized the significance of its meaning in relationship to necessity for an old age for the earth. “No vestige of a beginning, no prospect of an end.”.
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Siccar Point, Scotland The unconformable contact of Old Red Sandstone on vertical Silurian rocks noted by James Hutton, who in 1788 first recognized the significance of its meaning in relationship to necessity for an old age for the earth “No vestige of a beginning, no prospect of an end.” http://www.glg.ed.ac.uk/courses/field/siccarpt/
Earth Structure Earth starts as molten ball of rock. Elements begin to differentiate (layers based on density).
Earth Structure How do we know its structure? -- deepest drill only 7 miles deep. -- from earthquakes (seismic activity).
Seismic Waves P-wave: - faster S-wave: - slower - liquids stop wave. - cause most damage
Outer Layers Lithosphere (crust + hard upper mantle) - outermost layer of Earth - includes continents and ocean floor Asthenosphere = plates move on this. Convection occurs here.
Inner Layers Mantle - mostly solid rock - 80% of Earth’s volume. Outer Core -liquid iron/nickel - rotation creates magnetic field. Inner Core= solid iron.
Magnetic Field Outer core creates magnetic field Protects us from solar wind (radiation). Magnetic field reverses every 10k to 1,000,000 years.
Crust Continental Crust Oceanic Crust -- more dense -- younger (why?) -- less dense -- older
Plate Tectonics Alfred Wegener - 1915 (Continental Drift) Evidence: • Continents fit like a jigsaw puzzle. • Same geology on each side of ocean. • Fossils of land animals on each side of ocean.
Proof Not until the 1960’s. Seafloor spreading hypothesis: If the seafloor is spreading, then magnetic reversals will match on each side of the spreading ridge.
