# What is one advantage of radioactive dating over relative dating

It has the same number of protons, otherwise it wouldn't be uranium.The number of protons in the nucleus of an atom is called its atomic number.Therefore the amount of argon formed provides a direct measurement of the amount of potassium-40 present in the specimen when it was originally formed.Because argon is an inert gas, it is not possible that it might have been in the mineral when it was first formed from molten magma.The amount of strontium-86 in a given mineral sample will not change.Therefore the relative amounts of rubidium-87 and strontium-87 can be determined by expressing their ratios to strontium-86: Rb-87/Sr-86 and Sr87/Sr-86 We measure the amounts of rubidium-87 and strontium-87 as ratios to an unchanging content of strontium-86.(Creationists claim that argon escape renders age determinations invalid.

The formula for the fraction remaining is one-half raised to the power given by the number of years divided by the half-life (in other words raised to a power equal to the number of half-lives).

(Do not confuse with the highly radioactive isotope, strontium-90.) Strontium occurs naturally as a mixture of several nuclides, including the stable isotope strontium-86.

If three different strontium-containing minerals form at the same time in the same magma, each strontium containing mineral will have the same ratios of the different strontium nuclides, since all strontium nuclides behave the same chemically.

It can be readily seen from the plots that when this procedure is followed with different amounts of Rb87 in different minerals, if the plotted half life points are connected, a straight line going through the origin is produced. The steeper the slope of the isochron, the more half lives it represents.

When the fraction of rubidium-87 is plotted against the fraction of strontium-87 for a number of different minerals from the same magma an isochron is obtained.