Right now I'm reading a fossils text: Life History of a Fossil, Pat Shipman, Harvard University Press, 1981, supposedly for advanced undergraduates and professionals. (This isn't for a class. I just saw the book and picked it up.) All these fairy tales have interesting segments. So here's one from this book:
Both radiometric and paleomagnetic dating are widely used to date rocks older than 100,000 years. Radiometric dating depends on the fact that radioactive atoms in the original environment are captured as the rocks solidify. Such atoms degenerate at a steady rate by giving off particles from their nuclei. Over time these atoms become either a new isotope of the original element or a new element. The time elapsed since the rock has lithified can be determined by measuring the proportions of the original parent atoms and the new daughter atoms. Of course if the rocks are reheated to a new molten state after their original lithification, the proportion of atoms will reflect the most recent heating and cooling, not the original one.Well, silly me. Here, all along, I didn't think terrestrial heating or cooling could cause nuclear reactions. It just goes to show that all that Atomic and Nuclear Physics I took was a waste of time.
Still, I'd like to know about that 7000 mile diameter earth. To me the fact that no one even seems to want to guess indicates that they really don't know much about the 8000 mile diameter earth either.
ML/NJ