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Terrestrial Worlds 2 Earth - The most unique of all
Earth basics • 3rd planet from Sun (1 AU), 5th largest world • Orbit - 1 Earth year • Sidereal rotation - 23.9 hours (solar day -24 hrs) • Surface gravity- 9.8 m/s2. • 1 bar of pressure • 78% N2 21% O2 < 1% others 0.003 CO2. • Temperatures- ~100oF summer (max. 140oF, deserts) - ~0 oF winter (min. -130 oF, poles)
Unique Features • oceans, • Plate tectonics • oxygen atm. • Life!
Earth -Bimodal heights Broad regional highs (continents) Broad regional lows (ocean basins) 4 km difference
Earthquakes Detected earthquakes form lines
Earth’s crust broken into pieces ~8 large and 10 small plates
Rising current (hot) Plate dragged aside Breaks at weakest point (where it is hottest) New lava wells into gap. DIVERGENT boundary Falling current drags plate after it. 1 plate hits another and sinks. CONVERGENT boundary Crust follows Convection Currents
Why Does This Happen? • The plates float on a semi-liquid layer called the asthenosphere • The liquid allows slabs to slide under each other.
Earth -tectonics • All a consequence of internal convection: • Extension faults occur at upwelling of mid-ocean ridges (divergent boundary) • Compression faults occur at downwelling of subduction zones (convergent boundary) • Strike-slip faults occur as plates jostle around,
Earth -Volcanism • All a consequence of internal convection: • Low viscosity lavas occur at upwelling of mid-ocean ridges -shield volcanoes • High viscosity lavas occur at subduction zones as crust is remelted - tall, explosive, stratovolcanoes Result: Earth is the ONLY world to have stratovolcanoes, because it’s the only world to have plate tectonics
Earth - Erosion & Surface processes • Mass wasting • Wind -deserts • Biological (unique) • Water -main process • River Channels erode at head, deposit at mouth • Materials move along beaches • Glaciers grind material down
Earth -Cratering Earth has about 200 craters at the surface.
Earth’s Volatiles(atmosphere and hydrosphere) Earth is unique in that: • the majority of it’s volatiles are liquid. • Atmospheric composition is not all CO2(78% N2 , 21% O2 ,<1% others, 0.003 CO2 ) • Life affects the atmospheric balance.
Four Important Questions • Why did Earth retain most of its outgassed water? • Why does Earth have so little atmospheric carbon dioxide, unlike Venus? • Why does Earth’s atmosphere consist mostly of nitrogen and oxygen? • Why does Earth have a UV-absorbing stratosphere?
Earth Oceans and Temperature Why does Earth have oceans while Venus and Mars do not? • Earth is the right temperature to have liquid water due to distance from the Sun. • Temperatures are maintained by moderate greenhouse warming • CO2 balance maintained by oceans and life • (they act as a sink for all the CO2 that would otherwise be in the atm. making extra warming) • Magnetic field prevents H2O breakup.
Why Does Earth have a Nitrogen/Oxygen Atmosphere? • Most of the CO2 is locked up. Nitrogen is the main ingredient left. • Plant life produces oxygen, as plants increase oxygen levels increase. Large excess over time. • Some of excess oxygen gets broken and remade into ozone • (3 O2 molecules become 2 O3)