Problems with relative dating
Plus, get practice tests, quizzes, and personalized coaching to help you succeed.PART 1: Back to Basics PART 2: Problems with the Assumptions PART 3: Making Sense of the Patterns This three-part series will help you properly understand radiometric dating, the assumptions that lead to inaccurate dates, and the clues about what really happened in the past.Obviously, these eruptions took place very recently, after the Canyon’s layers were deposited ().These basalts yield ages of up to 1 million years based on the amounts of potassium and argon isotopes in the rocks.However, unlike the hourglass whose accuracy can be tested by turning it upside down and comparing it to trustworthy clocks, the reliability of the radioactive “clock” is subject to three unprovable assumptions.
To date a radioactive rock, geologists first measure the “sand grains” in the top glass bowl (the parent radioisotope, such as uranium-238 or potassium-40).But when we date the rocks using the rubidium and strontium isotopes, we get an age of 1.143 billion years.This is the same age that we get for the basalt layers deep below the walls of the eastern Grand Canyon.4 How could both lavas—one at the top and one at the bottom of the Canyon—be the same age based on these parent and daughter isotopes?Ngauruhoe, New Zealand (), yield a rubidium-strontium “age” of 133 million years, a samarium-neodymium “age” of 197 million years, and a uranium-lead “age” of 3.908 billion years!
8 Physicists have carefully measured the radioactive decay rates of parent radioisotopes in laboratories over the last 100 or so years and have found them to be essentially constant (within the measurement error margins).
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