Range of potassium argon dating
That is, a fresh mineral grain has its K-Ar "clock" set at zero.The method relies on satisfying some important assumptions: Given careful work in the field and in the lab, these assumptions can be met.These effects must be corrected, and the process is intricate enough to require computers.Ar-Ar analyses cost around 00 per sample and take several weeks.A variant of the K-Ar method gives better data by making the overall measurement process simpler.The key is to put the mineral sample in a neutron beam, which converts potassium-39 into argon-39.
But micas, plagioclase, hornblende, clays and other minerals can yield good data, as can whole-rock analyses.The Ar-Ar method is considered superior, but some of its problems are avoided in the older K-Ar method.Also, the cheaper K-Ar method can be used for screening or reconnaissance purposes, saving Ar-Ar for the most demanding or interesting problems.The rock samples are crushed, in clean equipment, to a size that preserves whole grains of the mineral to be dated, then sieved to help concentrate these grains of the target mineral.The selected size fraction is cleaned in ultrasound and acid baths, then gently oven-dried.With each increment in quality, more subtle sources of error have been found and taken into account.Whenever the worldview of evolution is questioned, this topic always comes up.The site also must be geologically meaningful, clearly related to fossil-bearing rocks or other features that need a good date to join the big story.Lava flows that lie above and below rock beds with ancient human fossils are a good—and true—example.Because Ar has a very short half-life, it is guaranteed to be absent in the sample beforehand, so it's a clean indicator of the potassium content.The advantage is that all the information needed for dating the sample comes from the same argon measurement. This method is commonly called "argon-argon dating."The physical procedure for K.