Isotope preferred dating very old rocks most intimidating college football chants
The pioneers of radiocarbon dating used this method because carbon-14, the radioactive isotope of carbon, is very active, decaying with a half-life of just 5730 years.The first radiocarbon laboratories were built underground, using antique materials from before the 1940s era of radioactive contamination, with the aim of keeping background radiation low.Consider this analogy: a barbecue grill full of burning charcoal.The charcoal burns at a known rate, and if you measure how much charcoal is left and how much ash has formed, you can tell how long ago the grill was lit.Counting a few million atoms (easy with just micrograms of rock) yields dates that are quite good.Isotopic dating has underlain the whole century of progress we have made on Earth's true history. That's enough time to fit all the geologic events we ever heard of, with billions left over.
The principle of using radioactive decay as a dating method is simple.No one knew even how much of Earth history was unknown!We needed a more precise tool, some sort of clock, to begin to measure it.For instance, the uranium-to-lead decay cascade is really two—uranium-235 decays to lead-207 and uranium-238 decays to lead-206, but the second process is nearly seven times slower.(That makes uranium-lead dating especially useful.) Some 200 other isotopes were discovered in the next decades; those that are radioactive then had their decay rates determined in painstaking lab experiments.