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How is the uranium to lead ratio in a rock used to estimate its age? How does this dating technique provide an estimate for Earth's age? How old is Earth according to this dating method?
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This decay process happens over a long period of time, with a half-life of about 4.5 billion years. Show more…
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What is one assumption in the use of the uranium/lead ratio for dating ancient geologic formations?
A radiometric dating technique uses the decay of $\mathrm{U}-238$ to Pb-206 (the half-life for this process is 4.5 billion years) to determine the age of the oldest rocks on Earth and by implication the age of Earth itself. The oldest uraniumcontaining rocks on Earth contain approximately equal numbers of uranium atoms and lead atoms. Assuming the rocks were pure uranium when they were formed, how old are the rocks?
As a geologist, you're assessing the feasibility of determining the ages of Earth's earliest rocks using radioactive dating. You estimate the number of half-lives that have passed for three different isotopes during Earth's 4.5 -billion-year lifetime, and from that you determine the number of atoms remaining today from $10^{6}$ atoms present at Earth's formation. The isotopes you consider are carbon- $14,$ uranium-238, and potassium-40. What are your estimates, and which isotopes do you conclude are suitable for radioactive dating?
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