The global distribution of marsupials as it relates to plate tectonics and continental drift:
Marsupials are located only in Australia and the Americas. This is because the marsupials evolved as the continents drifted around. At a crucial time period, Australia, Antarctica, and South America were attached together and seperate from Africa and Eurasia.
What drives continental drift? endogenic energy given off by radioactive decay in the interior of the earth causes convection currents in the earth's interior. As the plastic layer of the mantle convects and forms convection loops, it drags pieces of the crust around the surface.
I distinguished endogenic energy given off by radioactive decay in the interior of the earth from the exogenic energy of the sun that has driven most of the processes covered so far this quarter (wind, weather, ocean currents).
The Rock Cycle:
a combination of endogenic and exogenic processes produce three broad catogories of rock: igneous, sedimentary, and metamorphic.
Igneous rock is formed from completely melted material (magma) that hardens. There are two forms of igneous rock -
-extrusive volcanic rock which cools very quickly at the surface to form very small crystals (or no crystaline structure in the case of obsidian glass).
-intrusive igneous rock where magma cools very slowly underground forming large crystals.
Sedimentary rock is formed by the weathering, erosion, transportation, and deposition of rocks. When the resulting sediments go through a process of lithification (compaction, cementation,hardening) they form a clastic sedimentary rock (made up of bits and pieces of other rock).
When minerals dissolved in water precipitate out of the solution, or the water evaporates away, this forms a chemical sedimentary rock.
Metamorphic rock results from the alteration of igneous, sedimentary, or other metamorphic rocks. When buried deep enough to undergo extreme heat and pressure, the crystaline structure of the rock is partially melted and reformed in a much harder, denser structure. Water can also play a role in metamorphism.
Igneous rock was melted magma that hardened.
Sedimentary rock is made from materials that settled out of water.
Metamorphic rock is altered to make it harder and more dense.
Next Monday, I will finish up chapter 8 with examples of these rock types, and a review
of plate tectonics.