Lecture #22: (Monday March 20)

I. Formation of terrestrial planets
-- they from from the materials that can "stick together" at the local temperature in the disk (which gets hotter the closer to the Sun)
-- metals can stick together at the highest temperatures, then rocks, then ices
-- large planets, moons, and asteroids initially form very hot, both because of gravity and because of internal radioactivity
-- over time, they cool, as the radioactivity dwindles and the heat escapes
-- smaller bodies will cool faster, just like food from the oven
-- larger bodies should still have molten interiors and be volcanic
II. Buoyancy
-- when a planet's interior is molten, then bouyancy will separate the various interior substances
-- importance of density- Eureka!
-- floating objects displace their weight, sunk objects displace their volume
-- if a floating object must displace its weight, what it is floating in must be denser than the object itself or it would have to displace more than its own volume in order to float
-- for a rock to float up to the crust of a planet, it must be less dense than the other rocks and metals
III. Differentiation
-- the separation of materials that occur in a molten interior, when low density things float and high densities sink
-- occurs for large enough bodies to get hot enough to become molten
-- denser metals (Fe) sink, lighter elements (Si and O) rise to mantle
-- core is metallic (iron, nickel), mantle is rocky (granite,basalt)
-- rough densities: metal -> 8 g/cm^3 , rock -> 3 g/cm^3, ice -> 1 g/cm^3
IV. Initial structures
-- chondrules (small spherical balls of cooled molten rock, basic building block)
-- glasses (cool quickly, "frozen" into random configurations)
-- crystals (cool slowly, plenty of time to reach a regular array)
IV. Rocks
-- igneous: basalt (dark- come from deeper, less Si and O) and granite (lighter- come from higher up, more Si)
-- sedimentary: surface phenomena- shale and sandstone
-- metamorphic: reprocessed chemically or by pressure- diamond, slate, marble
V. Surface formation
-- regoliths and breccias (due to impacts)
-- cratering (see the Moon)
-- magma flows (due to internal heat) (see Mars' Olympus Mons)
-- geologic activity: subduction, earthquakes, mountains (see Mars' Valles Marineris)
-- erosion by air and water (see Grand Canyon)