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°-In these reactions, the isotope that undergoes decay is the parent isotope, while the decay product is the daughter isotope.
°-Physicists cannot specify how long an individual radioactive isotope will survive before it decays, but they can measure how long it takes for half of a group of parent isotopes to decay (half life of the isotope). °-For a given decay reaction, the half-life is constant. °°Half Life (in the context of radioactive decay)°°°-Example:U238 is the parent, Pb is the daughter. 4.47B years is the amount of time need to convert half the mass of U to Pb. °-Half life useful technique°-UPb used to age very old rocks°-CN used to age very young rocks°-Half life measure can be used to date rocks in betweenPick isotope, look at the half life, and see if its appropriate for the rocks you’re looking at. °-We’re not dependent on half life, we can date rocks when we have a small amount of parent/daughter (1/2 life is just a guide)°-In reality, they can use carbon dating to date anything that’s 80k years and younger. °-Half life is incorporated into the formula below. °°-Formula: N0: The initial number of parent atoms. If that’s not given, just add the number of parent atoms and the number of daughter atoms. Lambda: The rate of decay per year
N is the number of parent atoms at time tWhen N is ½, there are equal number of parent and daughter atoms°-Can arrive at time°°Radiocarbon Dating- How to Apply°-Used to date recent objects°-The atmosphere contains 78% nitrogen°-There’s a process called cosmic radiation, which is a reaction where Nitrogen is turned into Carbon (reduces number of protons by 1)°-Plants take in this carbon dioxide to build (C14 that was created from cosmic radiation)°-The organism dies quickly (grass), we can take that material and date it. °-It’s concentration will remain stable until the organism dies (it won’t take in any more C14). °-At that point, the C14 reaction decays at a constant rate into N14°-Apply equation. We know the decay rate, we can measure the C14 andthe N14 in the organism. From that, the time elapsed since the organism died can be found. °
Origin and Evolution of Life11/26/2014°The Oldest Life on Earth°°-Where does evidence of early life comes from? Rocks called chert (finegrain silica)°-Side-note: Fossilized tree-trunks are all silica (silicon dioxide) (no organic matter)°-The bacteria we’re looking at have been fossilized. (fossilized in rock that are 3.5B years old- chert). °°Extraterrestrial life?°-Possible evidence that comes from 2 meteorites°-Interesting thing: their carbaonatious condrites (they have a lot of carbon in them)°-People have been able to extract amino acids from them (the building blocks of life). °-Controversial: someone claimed to analyze a piece of one of the meteorite, magneto tactic bacteria (and then compares it to modern day bacteria).