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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?An hourglass is a helpful analogy to explain how geologists calculate the ages of rocks.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.Once you find your worksheet, click on pop-out icon or print icon to worksheet to print or download. You can & download or print using the browser document reader options.
Part 2 explains how scientists run into problems when they make assumptions about what happened .
Similarly, as molten lava rises through a conduit from deep inside the earth to be erupted through a volcano, pieces of the conduit wallrocks and their isotopes can mix into the lava and contaminate it.
Because of such contamination, the less than 50-year-old lava flows at Mt.
To make matters even worse for the claimed reliability of these radiometric dating methods, these same basalts that flowed from the top of the Canyon yield a samarium-neodymium age of about 916 million years,5 and a uranium-lead age of about 2.6 billion years!
6 The problems with contamination, as with inheritance, are already well-documented in the textbooks on radioactive dating of rocks.7 Unlike the hourglass, where its two bowls are sealed, the radioactive “clock” in rocks is open to contamination by gain or loss of parent or daughter isotopes because of waters flowing in the ground from rainfall and from the molten rocks beneath volcanoes.
They also measure the sand grains in the bottom bowl (the daughter isotope, such as lead-206 or argon-40, respectively).