In the initial state, the graph of daughter isotope to the third isotope versus parent isotope to the third isotope should result in a straight, horizontal line.The process of evaluating the daughter product as a ratio against another isotope of the same element is a valid method because, when a mineral or rock forms from a homogenous state, the elements that are assimilated into crystalline formation are very restricted.This initial ratio allows the non-daughter product isotope to be representative of the initial amount of the daughter product (Stassen 1998).As time progresses and decay occurs, the number of atoms of the parent isotope decreases, and the number of atoms of the daughter isotope increases accordingly.Indeed, the traces of uranium-238 in the star's atmosphere could have come from just one supernova.The uranium-238 absorption lines are relatively easy to detect in metal-poor stars because they are not obscured by the strong absorption lines of other metals.'In the next few years, we expect to find perhaps 10 or 20 of these stars.' Other methods of dating the universe - such as measuring how quickly galaxies recede from us - are less reliable because they are based on untested assumptions about the evolution of the universe.Radioactive decay has become one of the most useful methods for determining the age of formation of rocks.
Taking into account uncertainties about the initial abundance of elements, Cayrel's and co-workers have obtained an estimate of 12.5 billion - or 12.5 x 10 - years old, plus or minus just 3 billion years.
However, isochron dating bypasses this assumption, as explained below. The final condition is the number of atoms of parent and daughter isotopes remaining in the rock and can easily be measured in a lab.
Isochron dating bypasses the necessity of knowing the quantity of initial daughter product in the rock by not using that value in the computation.
The possible range of ages for the universe will also narrow as we learn more about the ratios in which elements are created in stars.
'We are already planning new surveys to discover other metal-poor stars in which we can measure the abundances of uranium and thorium,' said Timothy Beers, a member of the research team based at Michigan State University.