CORNELL ASTRO 202 - Age of the Solar System (9 pages)

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Age of the Solar System



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Age of the Solar System

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Lecture Notes


Pages:
9
School:
Cornell University
Course:
Astro 202 - Our Home in the Solar System

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What is the best way to tell how old the solar system is By studying rocks ASTRO 202 Age of the Solar System Rocks from where Anywhere we can find them as long as they are old Thursday February 21 2008 To date Earth rocks we are here so easy Prof Don Campbell Lunar rocks we went there and collected them Mars rocks some hit the Earth after being blasted off Mars Meteorites they hit the Earth and we collect them Space particles we collect them with spacecraft Beta decay How do we tell the age of a rock or particle Rubidium Strontium dating By looking at its isotopic composition Alpha decay Brown are protons always 8 so an the nucleus of an oxygen atom Uranium lead dating Green are neutrons number can vary making different isotopes 1 Parent Isotope Daughter Isotope Half life millions of years Decay Constant yr 1 40K 40Ar 1 250 5 81 10 11 87Rb 87Sr 48 800 1 42 10 11 Number of parent atoms number of daughter atoms constant Potassium K has 19 protons Argon Ar 18 so Beta decay via capture of an electron by the nucleus converting a proton to a neutron Rubidium Rb has 37 protons Strontium Sr has 38 so Beta decay by losing an electron from nucleus converting a neutron to a proton Oldest rocks on Earth are Acasta Gneisses in northwestern Canada near Great Slave Lake 4 03 billion years Gneisses are sedimentary or igneous rocks that are heavily modified by high temperatures and pressures The Acasta Gneisses are granitic igneous rocks that have been metamorphosed Isua sedimentary rocks in West Greenland 3 7 to 3 8 billion years Zircon crystals with Uranium Lead ages of 4 4 billion years have recently been reported from younger sedimentary rocks in west central Australia From USGS 2007 Cleaned exposures of the Acasta gneisses at their discovery site Ancient tonalites an igneous plutonic intrusive rock 4 03 billion years occur on left side of the picture and are intruded by highly deformed younger granite sheets and mafic dykes 2 The 4 4 billion year old Zircon crystal ZrSiO4



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