Because of such contamination, the less than 50-year-old lava flows at Mt.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!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.
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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.
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.
Radioactive rocks offer a similar “clock.” Radioactive atoms, such as uranium (the parent isotopes), decay into stable atoms, such as lead (the daughter isotopes), at a measurable rate.
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?
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.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.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.The rate of uranium decay must have been at least 250,000 times faster than today’s measured rate! As this article has illustrated, rocks may have inherited parent and daughter isotopes from their sources, or they may have been contaminated when they moved through other rocks to their current locations.Or inflowing water may have mixed isotopes into the rocks.Yet the same uranium decay also produced abundant helium, but only 6,000 years worth of that helium was found to have leaked out of the tiny crystals. Not Billions (Master Books, Green Forest, Arkansas, 2005), pages 65–78.