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Lecture 4

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Lecture FourSeptember 14 2011Time Scale of Earth History Age of universeo 13514 Ga giga annumbillions of years o Based onastronomical theorymodels Hubble Space TelescopeAge of Sun and solar systemo 457 Ga o Based on models of stellar evolution and dating of primitive solar system objectsCarbonaceous chondrites meteoritesAge of Earth o 454 Ga o Based on ages of terrestrial rocksage of solar systemmodels of solar system formationNo rocks this old found on Earth whyPlate tectonics volcanic lavas weathering and erosion Oldest around 42 Ga check into it found in Canadian shield Nebular Theory Interstellar cloud inherits elements from previous generations of starso Rotation o Gravitational collapse o Solar nebula is formed Clouds of dust gas and material pockets of air that has gravitational pull and coalesces into a denser massAs it comes together the gravitational attraction becomes stronger and you end up with a much denser mass instead of loose cloud of gas and dust o Eg having a super nova occur nearby causing this material to collide and begin that process of gravitational collapseThrough this process stars are formedMaterial at centre has highest temperature and pressure where everything is coming together o Outer area is cooler and lower pressurePhysics of rotating mass of loose material dictate that it will flatten into a disk everything is more or less rotating in the same directionIf material at the centre of nebula can get dense enough fusion can occur o Fusing two atoms together o Eg fusing to hydrogen atoms together to make a helium atom o When centre has high enough pressure and nuclear fusion occurs that is when you can consider it a star o Lots of circumstances where it doesnt get to that point though start never has nuclear fusion and giving out energyOur sun did get to the point of nuclear fusion o Source of its energy is nuclear fusion o Eg going outside and feeling the suns radiationo Fusing two hydrogen atoms together a little bit of mass left over that turns into energyCondensation
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