announcements 25 people have still not joined the class on astronomy place. you can not get credit...
Post on 22-Dec-2015
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Announcements
• 25 people have still not joined the class on Astronomy Place. You can not get credit until you “join the class”. Once you join, all your previous submissions will show up in my gradebook.
• Planet Assignment 4, due Monday March 1, – Part 1: Astronomy Place tutorial “Shaping
Planetary Surfaces”– Part 2: Angel Planet Assignment 4
Objectives:
• Describe the significance of bombardment in the early solar system.
• Compare and contrast the structure & evolution of the terrestrial planets.
• Describe the differentiation into core, mantle & crust.
• Describe the heating and cooling processes in planetary interiors. Describe the importance of planetary size on its evolution.
When Planets Form - Bombardment & Differentiation
• Bombardment of planet as it forms, HEATS and melts its surface
• Molten iron and other heavy elements sink toward the center
• Falling iron converts gravitational potential energy to kinetic energy -> HEAT
Inside the Terrestrial Worlds
• After they have formed, the molten planets differentiate into three zones:• core - made of metals• mantle - made of dense rock• crust - made of less dense rock
• Lithosphere - the rigid, outer layer of crust & part of the mantle which does not deform easily
Heating the Planets
• Planetary interiors heat up through:• accretion
• differentiation
• radioactivity
Supplies all the heat at the beginning
Supplies heat throughout the planet’s life
Cooling the Planets
• Planets Cool by Radiating Heat to Space from their Surface
• Heat is Transported from the Interior to the Surface by:• conduction - atoms & molecules moving &
hitting other atoms & molecules• convection - macroscopic flows: hot material
rising & cool material sinking
Role of Planetary SIZE
• Larger planets heat more– More iron to flow to center– More radioactive elements to split
• Larger planets cool slower– Extra layers provide extra insulation
Role of Planetary Size
• Heating proportional to Volume ~ R3
• Cooling proportional to Surface Area ~ R2
• Heating/Cooling ~ Volume/Area ~ R = Size
• Smaller Planets Cool Faster & Heat Less(by impacts and splitting of radioactive nuclei)-> Thicker rigid Lithosphere -> Less volcanism & Tectonic Activity
How do we Know about the Interior of Earth
• Earthquakes make waves
• Waves travel through Earth, the higher the density the faster the waves travel
• Two types of waves– Back & forth
– Side to side
Shaping Planetary Surfaces
• Major geological processes that shape planetary surfaces:• impact cratering: excavation of surface by asteroids or
comets striking the planet• volcanism: eruption of lava from interior• tectonics: disruption of lithosphere by internal stresses• erosion: wearing down by wind, water, ice
Counting Craters to find Surface Age • Cratering rate decreased as Solar Systems aged.
• The older the surface, the more craters are present.
History of Plate Tectonics
• South America and Africa fit together like a jig-saw puzzle, with matching geological formations and fossils
• New Idea (Wegner 1912)Continental Drift
• Rejected by Geologists– Counter to established ideas– Lack of overwhelming evidence– No mechanism to drive motions