Biogeography Chapter 8

• Looking at index fossils.
• Largely limited to determine geological events.
• Determines sequential order which a series of events occured

• Using radiometric dating techniques.
• Computes numerical age.
• Example: Carbon 14 (organic matter) 1/2 life=5730 years to upper limit 40,000 years.

Thought the supercontinent was fragmented by the Great Flood in the Bible

• Contraction theory: Earth cooled, shrank, and deformed creating mountains and ocean basins.
• Arching pressure under compression formed mountains.

• Permanence Theory: Locations of continents and ocean basins were permanent.
• Positions of continents may have changed, but not in relation to each other.

• 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)

• 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).

• Fit of continents
• Plants and animals match
• Rocks match
• Ice movement matches
• Climates were different positions do not match

• 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.

• In the 1950s and 1960s ocean cores were recovered and showed reversing polarity.
• rock was much younger than expected
• proved seafloor spreading

Earth's crust is broken into many pieces, called 'plates' and these move in specific ways to create all the earth's features.

• 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

• 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

• Pangea- Supercontinent (late Permian)
• Gondwana- South America, Africa, Australia, India, Antarctica
• Laurasia- North America, Asia, Europe

• Changes in total solar irradiance
• Indirect effects of ultraviolet radiation on stratosphere

• 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.

Surface albedo (reflectance of sun on land masses)

• 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)

• 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.