The energy-level diagram below is based on data accumulated by McDougall and Harrison. Despite 40 Ca being the favored daughter nuclide, it is rarely useful in dating because calcium is so common in the crust, with 40 Ca being the most abundant isotope. It's a pretty good indicator, if you can assume that this soil hasn't been dug around and mixed, that this fossil is between million and million years old. There are also complications with the atomospheric argon content and various argon contamination scenarios. So it allows you, even though you're only directly dating the volcanic rock, it allows you, when you look at the layers, to relatively date things in between those layer. Now, we also know that not all of the atoms of a given element have the same number of neutrons.
When rocks are heated to the melting point, any Ar contained in them is released into the atmosphere.
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Video transcript We know that an element is defined by the number of protons it has. Ar—Ar dating is a similar technique which compares isotopic ratios from the same portion of the sample to avoid this problem. And when we talk about a given element, but we have different numbers of neutrons we call them isotopes of that element. Conversion to stable 40 Ar occurs via electron capture in the remaining And you dig enough and you see a volcanic eruption, you see some volcanic rock right over there, and then you dig even more. With 18 protons and 22 neutrons, the atom has become Argon Aran inert gas. Since potassium is a constituent of many common minerals and occurs with a tiny fraction of radioactive potassium, it finds wide application in the dating of mineral deposits.