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One solution is that both the recent and early lava flows inherited the same rubidium-strontium chemistry—not age—from the same source, deep in the earth’s upper mantle.
This source already had both rubidium and strontium.
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.
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.
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.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.No geologist was present when the rocks were formed to see their contents, and no geologist was present to measure how fast the radioactive “clock” has been running through the millions of years that supposedly passed after the rock was formed.Furthermore, they have not been able to significantly change these decay rates by heat, pressure, or electrical and magnetic fields.So geologists have assumed these radioactive decay rates have been constant for billions of years.
They also measure the sand grains in the bottom bowl (the daughter isotope, such as lead-206 or argon-40, respectively).