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Relative Dating
- Looking at index fossils.
- Largely limited to determine geological events.
- Determines sequential order which a series of events occured
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Absolute Dating
- Using radiometric dating techniques.
- Computes numerical age.
- Example: Carbon 14 (organic matter) 1/2 life=5730 years to upper limit 40,000 years.
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Antonio Snider-Pellegrini
Thought the supercontinent was fragmented by the Great Flood in the Bible
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Europe thinking before drift and Tectonic Theory
- Contraction theory: Earth cooled, shrank, and deformed creating mountains and ocean basins.
- Arching pressure under compression formed mountains.
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US thinking before drift and Tectonic Theory
- Permanence Theory: Locations of continents and ocean basins were permanent.
- Positions of continents may have changed, but not in relation to each other.
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Alfred Wegener and Tectonic Theory
- Contraction/Permanence ignored facts about geology and biogeography.
- Movements of continents show paleonotolgical evidence of species distribution.
- Agreement between paleontologists that continents connected during Carboniferous.
- Due to isotasy, it's impossible for a landbridge to sink (proves contraction theory wrong)
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How did Alfred Wegener prove Contraction Theory wrong?
- Radioactive materials produced heating (not cooling)
- Places where tension (not compression) produced topographic highs
- Alps had overthrust--multiple layers of rock (not arching)
- Most marine rock on continents was shallow (not deep having been thrust up from ocean basins).
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Multiple lines of evidence of continental drift
- Fit of continents
- Plants and animals match
- Rocks match
- Ice movement matches
- Climates were different positions do not match
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Skepticism for Wegener's theory
- Biogeographic evidence weak and could be explained without moving continents.
- Rates of movement were too high and geologic evidence was still unconvincing
- He couldn't identify clear mechanism by which solid continents move through ocean basins. He suggested molten convective currents, but didn't have evidence.
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Ultimate Acceptance of continental drift
- In the 1950s and 1960s ocean cores were recovered and showed reversing polarity.
- rock was much younger than expected
- proved seafloor spreading
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Theory of Plate Tectonics
Earth's crust is broken into many pieces, called 'plates' and these move in specific ways to create all the earth's features.
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Interactions between plates
- Transform Faults- 2 plates move past each other and create linear scars (Ex San Andreas Fault).
- Continental Collision- 2 plates collide, form high mountains (converging)
- Subduction- create linear volcanic mountain ranges like the Cascades in OR and WA. Subducts underneath other crust.
- Seafloor Spreading
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Hot Spots
- Fixed locations where magma comes through the mantle and creates volcanoes.
- Do not occur at plate boundaries
- Show us the direction of plate movement because the active volcano is over the hot spot and extinct volcanoes show the direction that the plate is moving.
- ex: Hawaii
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Pangea, Gondwanaland, Laurasia
- Pangea- Supercontinent (late Permian)
- Gondwana- South America, Africa, Australia, India, Antarctica
- Laurasia- North America, Asia, Europe
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Effects on Climate: Solar
- Changes in total solar irradiance
- Indirect effects of ultraviolet radiation on stratosphere
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Effects on Climate: Orbital (Milankovitch's theory of Orbital forcing)
- Variations in Earth's orbit- the shape around the orbit around the sun.
- Changes in obliquity (Tilt) changes the angle that Earth's axis makes with the plane of the Earth's orbit
- Change in direction of the Earth's axis rotation behaves like the spin axis of a top that is winding down.
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Effects on Climate:Configuration of land masses
Surface albedo (reflectance of sun on land masses)
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Effects on Climate:Atomospheric turbidity (aerosols)
- Strospheric
- Primary source of variation: volcanoes and asteroid impacts. Longer residence time and also a net cooling effect.
- Tropospheric (short residence time)- Salt from ocean waves, soot from combustion, or meteor impact, pollen volcanoes (cooling effect)
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Evidence of past climates
- Ice cores drawn from Greenland Antacrtica, and tropical mountain glaciers
- Show the Earth's climate responds to changes in solar output, in the Earth's orbit, and in greenhouse gas levels.
- Show large changes in climate have happened very quickly, geologically speaking.
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