# Rubidium 87 radiometric dating

*09-Apr-2017 09:53*

However, usually it is not possible to apply this formula directly, because, for instance, in many cases we do not know the original amount of the radioactive isotope when the rock was solidified.

Also, such a calculation does not provide us with any statistical error margin to double-check the result.

The corresponding dates obtained from these isochrons (based on the slopes of the lines), together with statistical standard deviations, are: 4.396 ± 0.18, 3.673 ± 0.014, 2.991 ± 0.15, and 4.478 ± 0.034 (each figure is in billions of years). But with the advent of mass spectrometry beginning in the 1970s, even very small samples can now be accurately dated.

For example, the "SHRIMP" ion microprobe now in use in numerous laboratories around the world can reliably measure U-Pb and Pb-Pb ages from spots only 0.02 mm (i.e., 20 micrometers) in size within a zircon crystal [Dalrymple2004, pg. It should be emphasized, though, that even relatively unsophisticated equipment can perform radiometric measurements of dates fairly well.

Note how breathtakingly close these points are to the fitted lines (thus confirming with high statistical confidence the validity of the resulting dates): The data for the first graph (upper left) is a set of measurements of basaltic achondrites (meteorites) in [Basaltic1981, pg.

938]; the data for the second graph (upper right) is from early Archaean gneisses rocks near Isua, Greenland [Morbath1977]; the data for the third graph (lower left) is from ancient gneiss rocks in Swaziland [Carlson1983]; the data for the fourth graph (lower right) is from lunar dunite rocks gathered during Apollo 17 [Papanastassiou1975]. For many years, fairly large samples were required to produce statistically reliable results.

Note that this equation is in the simple form y = b m x, namely the formula for graph of a straight line with slope m and with y-intercept b: here y = (Sr87/Sr86).Some have said that young-earth creationists will not be convinced of the scientific ages of the earth and fossils until they can measure these dates with their own hands. As mentioned above, radiometric dating methods are the basis for the figures in the detailed charts of the geologic ages, an abbreviated version of which is shown above.But radiometric methods are also used heavily in day-to-day research in paleontology and evolutionary biology, in order to test certain hypotheses.This technique, which is used in virtually all disciplines of modern social science, physical science and engineering, is entirely straightforward, and computer software is widely available to do the requisite calculations and, in fact, is built in to most spreadsheet programs.