Review 2 Astronomy 150, April 27 th 2005. Moon’s Formation Giant-Impact theory –A Mars-sized object hits the Earth and the Moon is created from the debris.
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Presentation on theme: "Review 2 Astronomy 150, April 27 th 2005. Moon’s Formation Giant-Impact theory –A Mars-sized object hits the Earth and the Moon is created from the debris."— Presentation transcript:
Moon’s Formation Giant-Impact theory –A Mars-sized object hits the Earth and the Moon is created from the debris –Lack of volatiles – impact was a high energy event and volatile elements evaporated –Lack of iron core – the Moon was created from Earth’s mantle debris – Earth was already differentiated iron was in the core low amounts of iron in the ejected debris –Similar Oxygen isotope ratios similar composition
Mars 4.5OriginOrigin by Accretion 4.5 – 4.0DifferentiationFormation of the original crust 3.9 – 3.8Late Heavy Bombardment Formation of Hellas Basin and the heavily cratered southern highlands 3.8 – 0.6Geological Activity Formation of the Tharsis region and the Northern volcanic plains 0.6 - NowThe Big ChillLow-level cratering and wind erosion Mineral Olivine – quickly dissolves in water it cannot last for long in wet environments Southern Hemisphere –Mineral Hematite – created in hot, wet environments –Evaporative basins – rocks get saltier as you move down the crater (as the Salt Lake) Lower gravity, lack of plate tectonics broad, tall shield volcanoes
Venus Thick atmosphere: –no continuous meteoritic bombardment (like on the Moon) jagged rocks –Lack of simple craters more complex craters, impact basins Rocks – basalts geologically active world lava flows, volcanoes, but no plate tectonics “blob” tectonics Surface remelts every 0.5 billion years How do we know that it went through 5 planetary stages?
Atmospheres Primary atmospheres – Hydrogen and Helium –Why don’t we have H & He atmospheres? The Sun, combustion/freezing removes atmospheres Secondary atmospheres - main source is outgassing gasses released when rocks melt Venus – thick, hot atmosphere due to the greenhouse effect CO 2 stops IR light (heat) emitted from the surface from leaving the planet Earth – very little CO 2 plants! –Rocks also absorb CO 2 rusting –Ozone layer absorbs UV light UV light does not break up water molecules we have water and Venus does not Mars – thin atmosphere, no ozone –CO 2 in polar ice caps