Sm nd isotopic dating
When combined with data on the precise concentration of samarium and neodymium in the rocks, this can reveal their age.The challenge comes from separating the three neodymium isotopes from the many other elements in the rocks, including samarium.Samarium-neodymium (Sm-Nd) dating is a process for determining the ages of rocks based on the radioactive decay of two samarium isotopes (Sm-147 and Sm-146) to two neodymium isotopes (Nd-143 and Nd-142 respectively).Sm-147 has a much longer half-life than Sm-146, but the concentration of both of them varies in different rock types, depending on exactly when the rocks crystallized from the parent magma.
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 various reservoirs within the solid earth will have different values of initial Nd ratios, especially with reference to the mantle.
The usefulness of Sm-Nd dating is the fact that these two elements are rare earths.
The production of radiogenic Sr can be expressed with respect to a reference isotope is the y-intercept ( which corresponds to Basalitc Achondrite Best Initial (or BABI) value for achondrite meteorites which gives an estimate of the initial Sr isotopic composition of the earth when it formed out of the solar nebula) and the slope of this line is proportional to the amount of time the rock has remained in a closed system with respect to Rb and Sr.
Sr will be higher in older crustal rocks and lower in younger rocks.
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.