What are the 4 types of radiometric dating
By definition, D* = N-1) (2) Now we can calculate the age if we know the number of daughter atoms produced by decay, D* and the number of parent atoms now present, N.The only problem is that we only know the number of daughter atoms now present, and some of those may have been present prior to the start of our clock. The reason for this is that Rb has become distributed unequally through the Earth over time.We can see how do deal with this if we take a particular case. For example the amount of Rb in mantle rocks is generally low, i.e. The mantle thus has a low If these two independent dates are the same, we say they are concordant.We can also construct a Concordia diagram, which shows the values of Pb isotopes that would give concordant dates.This little bundle is called an "alpha particle." Remember we said a neutron is a proton with an electron attached? Gamma rays (remember that term from when we studied the EMS? Gamma decay does not change the mass or charge of the atom from which it originates.In beta decay a neutron sends its electron packing, literally ejecting it from the nucleus at high speed. Gamma is often emitted along with alpha or beta particle ejecton.Other minerals that also show these properties, but are less commonly used in radiometric dating are Apatite and sphene.If a zircon crystal originally crystallizes from a magma and remains a closed system (no loss or gain of U or Pb) from the time of crystallization to the present, then the Discordant dates will not fall on the Concordia curve.
Thus, if we start out with 1 gram of the parent isotope, after the passage of 1 half-life there will be 0.5 gram of the parent isotope left.
But, again, exptrapolation of the discordia back to the two points where it intersects the Concordia, would give two ages - t* representing the possible metamorphic event and t and solve for t . This argument tells when the elements were formed that make up the Earth, but does not really give us the age of the Earth. Thus, our best estimate of the age of the Earth is 4.55 billion years.