Sr isotope dating
Sometimes, by chance these creatures also incorporate the element strontium into their shells -- strontium is an element in seawater that is chemically similar to calcium but found in much lower concentrations.For every 1000 calcium atoms, seashells contain just a few atoms of strontium. When diffusive isotope fractionation of Sr isotopes is repeated a sufficient number of times by within-mantle processes on isotopically-anomalous mantle xenoliths (each of which originally had low Sr ratios.
So how can Rb-Sr ‘isochrons’ be explained in the context of a young Earth?
The possibility of isotopic fractionation as an explanation for differences in Sr has been proposed to both authors on many occasions.
It therefore seems worthwhile to point out that isotopic fractionation does occur during the mass spectrometric ratio measurement.
Millions of years later, researchers can determine the age of marine fossils by extracting the strontium and comparing the ratio of the two isotopes with ratios known to have occurred in seawater in the past.
The Pliomax team uses this method of dating in laboratories specifically built for measuring strontium isotopes. The researchers work in a clean room with air 1000 times more pure than that on nearby city streets.