Editing Rubidium–strontium dating (section)

==Uses==
===Geochronology===
The Rb–Sr dating method has been used extensively in dating terrestrial and lunar rocks, and meteorites. If the initial amount of Sr is known or can be extrapolated, the age can be determined by measurement of the Rb and Sr concentrations and the <sup>87</sup>Sr/<sup>86</sup>Sr ratio. The dates indicate the true age of the minerals only if the rocks have not been subsequently altered.

The important concept in isotopic tracing is that Sr derived from any mineral through weathering reactions will have the same <sup>87</sup>Sr/<sup>86</sup>Sr as the mineral. Although this is a potential source of error for terrestrial rocks, it is irrelevant for lunar rocks and meteorites, as there are no chemical weathering reactions in those environments.

===Isotope geochemistry===
Initial <sup>87</sup>Sr/<sup>86</sup>Sr ratios are a useful tool in [[archaeology]], [[Forensic science|forensics]] and [[paleontology]] because the <sup>87</sup>Sr/<sup>86</sup>Sr of a skeleton, sea shell or indeed a clay artefact is directly comparable to the source rocks upon which it was formed or upon which the organism lived. Thus, by measuring the current-day <sup>87</sup>Sr/<sup>86</sup>Sr ratio (and often the <sup>143</sup>Nd–<sup>144</sup>Nd ratios as well) the geological fingerprint of an object or skeleton can be measured, allowing migration patterns to be determined.

===Strontium isotope stratigraphy===
Strontium isotope stratigraphy relies on recognised variations in the <sup>87</sup>Sr/<sup>86</sup>Sr ratio of seawater over time.<ref>{{cite journal |last1=Elderfield |first1=H. |title=Strontium isotope stratigraphy |journal=Palaeogeography, Palaeoclimatology, Palaeoecology |date=October 1986 |volume=57 |issue=1 |pages=71–90 |doi=10.1016/0031-0182(86)90007-6 }}</ref> The application of Sr isotope stratigraphy is generally limited to carbonate samples for which the Sr seawater curve is well defined. This is well known for the Cenozoic time-scale but, due to poorer preservation of carbonate sequences in the Mesozoic and earlier, it is not completely understood for older sequences. In older sequences diagenetic alteration combined with greater uncertainties in estimating absolute ages due to lack of overlap between other geochronometers (for example [[uranium–thorium dating|U–Th]]) leads to greater uncertainties in the exact shape of the Sr isotope seawater curve.<ref>{{cite journal |last1=Veizer |first1=Ján |last2=Buhl |first2=Dieter |last3=Diener |first3=Andreas |last4=Ebneth |first4=Stefan |last5=Podlaha |first5=Olaf G |last6=Bruckschen |first6=Peter |last7=Jasper |first7=Torsten |last8=Korte |first8=Christoph |last9=Schaaf |first9=Michael |last10=Ala |first10=Davin |last11=Azmy |first11=Karem |title=Strontium isotope stratigraphy: potential resolution and event correlation |journal=Palaeogeography, Palaeoclimatology, Palaeoecology |date=August 1997 |volume=132 |issue=1–4 |pages=65–77 |doi=10.1016/S0031-0182(97)00054-0 |bibcode=1997PPP...132...65V }}</ref>