Presentation on theme: "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."— Presentation transcript:
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 Siccar Point, Scotland No vestige of a beginning, no prospect of an end.
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. -- infer from earthquakes (seismic activity). We use P-waves and S-waves.
Seismic Waves Seismic = earthquakes P-wave: (pump) - fastest - travel completely through Earth. S-wave: (snake) - slow - no liquids - 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 Earths volume. Outer Core - liquid iron/nickel - rotation creates magnetic field. Inner Core = solid iron.
Plate Tectonics Alfred Wegener (Continental Drift) Evidence: -- Continents fit like a jigsaw puzzle. -- Same geology on each side of ocean. ex. Appalachian mountains, coal beds -- fossils of identical land animals on each side of ocean.
Mountain belts earlier than 260 ma
Magnetic Field Outer core creates magnetic field Protects us from solar wind (radiation). Magnetic field reverses every 10k to 1,000,000 years.
Proof Not until the 1960s. Seafloor spreading hypothesis: If the seafloor is spreading, then magnetic reversals will match on each side of the spreading ridge.