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Radio dating rocks

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When we look at sand in an hourglass, we can estimate how much time has passed based on the amount of sand that has fallen to the bottom.

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Or inflowing water may have mixed isotopes into the rocks.Yet this view is based on a misunderstanding of how radiometric dating works.Part 1 (in the previous issue) explained how scientists observe unstable atoms changing into stable atoms in the present.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.Most people think that radioactive dating has proven the earth is billions of years old.We find places on the North Rim where volcanoes erupted after the Canyon was formed, sending lavas cascading over the walls and down into the Canyon.

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.

But when we date the rocks using the rubidium and strontium isotopes, we get an age of 1.143 billion years.

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).

They also measure the sand grains in the bottom bowl (the daughter isotope, such as lead-206 or argon-40, respectively).

Part 2 explains how scientists run into problems when they make assumptions about what happened .