Rb sr dating problems

However, it is with the interpretation of the chemical analyses of the radioactive parents and resultant daughters that the problems with radioactive dating of rocks begin.In order to interpret these chemical analyses, geochronologists must make three vital assumptions, otherwise the radioactive ‘clock’ cannot be made to ‘read’ the ‘age’ of the rocks.magazine has been continuously published since 1978, we are publishing some of the articles from the archives for historical interest, such as this.For teaching and sharing purposes, readers are advised to supplement these historic articles with more up-to-date ones available by searching Snelling Some types (technically known as ‘isotopes’) of ‘parent’ elements such as uranium, thorium, potassium and rubidium are said to be radioactive because the nuclei of the atoms are unstable, resulting in readjustments between the ‘particles’ (primarily neutrons and protons) in the nuclei with time.

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Furthermore, even if today’s scientists believe they have the methods, for example graphical and mathematical, for determining how much of the daughter isotope might have been present either at the origin of the earth or the origin of the rock being dated, no one can ever be sure that these ‘answers’ are correct, because there was no scientist present at the beginning to observe those initial conditions, even though the scientists’ calculations may be extremely logical.Similarly, if the system has not remained closed (for example, if sand were somehow added or subtracted), then the calculation of the elapsed time, based on comparing the amounts of sand in the two glass bowls, will again lead to an incorrect conclusion.And finally, if the rate at which the sand grains fall from the top glass bowl to the bottom one varies (for example, moisture causes some clogging of the sand in the constriction between the two glass bowls), then again the hourglass ‘clock’ will be inaccurate.Or, some uranium might have been deposited by groundwaters into the sample, thus making it appear younger than what it really is.Indeed, geochronologists often plot the chemical analyses of the isotopes, expressed as isotope ratios, on graphs, and these often show that the parent-daughter systems have not been closed, but open.Now this ‘clock’ works because the initial conditions are known—that is, all the sand grains are in the top glass bowl and none are in the bottom one.If there is already some sand in the bottom glass bowl, then unless this amount is known the hourglass ‘clock’ cannot ‘tell’ the time.At time t = 0, the hourglass is turned upside-down so that all the sand starts in the top bowl.By time t = 1 hour, all the sand is supposed to have fallen into the bottom glass bowl.In the case of the initial conditions, no scientist can ever be sure as to what they were, because no scientist was present here on the earth at its origin.Thus the amount of daughter isotope that has actually been derived from the parent isotope by radioactive decay is unknown, since some of the daughter isotope might have been present with its respective parent isotope at the time of the earth’s origin.


  1. Oct 19, 2016. Mineral dating with Rb/Sr-Isotope system. ▫ Principles of isochron dating. known unknown. General problem two unknown parameters. Age determination by 14C/12C ratio. Carbon Isotopes. 12C stable. 14C radioactive decay constantly reformed in atmosphere. Approximate dating. N. 0. ≈ constant.

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