Radioactive isotopes used for dating
The late Francis Crick, the co-discoverer of DNA’s structure (along with James Watson and Maurice Wilkins), came to believe that aliens, and not God, were responsible for life on earth.‘There are some, again, who, though they do not suppose that this world is eternal, are of opinion either that this is not the only world, but that there are numberless worlds or that indeed it is the only one, but that it dies, and is born again at fixed intervals, and this times without number.’There is nothing new under the sun.
The first lesson, Isotopes of Pennies, introduces the idea of isotopes.
Games with manipulative or computer simulations should help them in getting the idea of how a constant proportional rate of decay is consistent with declining measures that only gradually approach zero.
The mathematics of inferring backwards from measurements to age is not appropriate for most students.
Radiocarbon dating uses isotopes of the element carbon. Cosmic rays – high-energy particles from beyond the solar system – bombard Earth’s upper atmosphere continually, in the process creating the unstable carbon-14. Because it’s unstable, carbon-14 will eventually decay back to carbon-12 isotopes.
Because the cosmic ray bombardment is fairly constant, there’s a near-constant level of carbon-14 to carbon-12 ratio in Earth’s atmosphere.