Radiometric dating rock types Free site chat hot ghana
In the case of carbon dating, it is not the initial quantity that is important, but the initial ratio of C, but the same principle otherwise applies.
Recognizing this problem, scientists try to focus on rocks that do not contain the decay product originally.
For example, in uranium-lead dating, they use rocks containing zircon (Zr Si O Zircon and baddeleyite incorporate uranium atoms into their crystalline structure as substitutes for zirconium, but strongly reject lead.
Zircon has a very high closure temperature, is very chemically inert, and is resistant to mechanical weathering.
Radiometric dating requires that the decay rates of the isotopes involved be accurately known, and that there is confidence that these decay rates are constant. The physical constants (nucleon masses, fine structure constant) involved in radioactive decay are well characterized, and the processes are well understood.
Careful astronomical observations show that the constants have not changed significantly in billions of years—spectral lines from distant galaxies would have shifted perceptibly if these constants had changed.
In fact, it is possible to shut down electron capture completely—simply ionize the substance so that there are no electrons nearby.
One assumption that can be made is that all the lead in the sample was once uranium, but if there was lead there to start with, this assumption is not valid, and any date based on that assumption will be incorrect (too old).
This is an example of the Weak force, and is fairly rare.
Electron capture requires that there be an electron in the vicinity of the nucleus, so its activity depends strongly on the configuration of the electron cloud, which depends on the chemical state.
There are a number of implausible assumptions involved in radiometric dating with respect to long time periods.
One key assumption is that the initial quantity of the parent element can be determined.
The effect of this on alpha decay, which is the most common decay mode in radiometric dating, is utterly insignificant.