Measure isotopes for radiometric dating

04-Nov-2019 13:54

How can the formation of a rock be correlated with a particular ancient event?The answers to all of these questions lie in our understanding of the geologic processes that affect the deposition of radioactive elements.These zircon crystals are tiny — just a tenth of a millimeter long — but they are the key to uranium-lead dating.If these crystals were pure, they would contain just zirconium, silica, and oxygen; however, uranium happens to have a similar arrangement of outer electrons to zirconium, and so as zircons form, "mistakes" are sometimes made, and uranium is substituted for zirconium.And in the next 704 million years, it will decay leaving behind ¼ gram, and in the next 704 million years, it will decay leaving behind ⅛ gram and so on.At the same time, the amount of the element that it decays into (in this case lead-207), will increase accordingly, as shown below. At what point on the graph would you expect the ratio of uranium to lead to be about 39 to 61?

With modern techniques, these ranges have gotten narrower and narrower, and consequently, even very ancient rocks can be dated quite precisely.In other words, the chance that a given atom will decay is constant over time.