Rubidium-strontium dating

The strontium isotope analysis uses include the analysis of ( pre) historic migration behavior of humans and animals. Strontium is added depending on the geographic location in different isotope ratios in the diet and stored in bones and teeth. The archeology has, ever since a few years more and more of this new method. The first projects came from the USA and Great Britain and first sought North and Central America. Current applications deal for example with the migration behavior in the Upper Paleolithic, Neolithic or Iron Age in Central Europe.

Newer applications use the effect of geographically - varying Sr isotopic composition, for food origin or authenticity - determination. For example, because certain regions are characterized by a characteristic Sr isotope signature, this signature is reflected among other things in various agricultural products. It should however be noted that there may be in the product by the entry of fertilizer and precipitation to the geological underground different Sr isotope signature. It is also called the " mobile Sr Group ". Further applications of the Sr - isotope analysis can be found for example in forensic medicine.

The radioactive rubidium - strontium -decay is suitable for the dating of rocks of Precambrian age.

Physical Basics

Strontium has four stable, naturally occurring isotopes: 84Sr (0.56 %), 86Sr ( 9.86% ), 87Sr (7.0%) and 88Sr ( 82.58 %). 87Sr is formed when β - decay of rubidium isotope 87Rb with a half-life of 4.81 · 1010 a Since the life of 86Rb is short, arises from already during the formation of the rock 86Sr. This is the isotopic ratio of 87Sr to 86Sr evidence of age of the rock. Depending on the region varies, the average 87Sr / 86Sr ratio of 0.71 up to 2%.

Deposition in bones and teeth

Strontium is an alkaline earth metal such as calcium. Therefore, it is used in the body as well as calcium for building bones and teeth. Since the development of the teeth is completed in adolescence, however, renew the bone constantly find themselves depending on where the person grew up and where she was in the last years, different isotope ratios. This will, for example, an analysis of migration movements sedentary populations made ​​possible if the strontium isotopes to fossil record can be used.

Benefits and drawbacks

Requirement for the application and a mapping of rocks. Inevitably provides a mapping of the strontium isotope ratios ambiguities. Therefore, the strontium isotope analysis alone is not sufficient. Therefore, further evidence must be consulted for the analysis of migration, such as foreign cultural artifacts in graves.

Other confounding factors are also the sales of food over long distances. This makes the isotopic analysis of cultures like ancient Rome more difficult, but also shows early knowledge of distribution on.

Rubidium - strontium dating

The half-life of 87Rb is about 10 times higher than the estimated age of the earth. Rubidium - strontium dating is based on the decay of rubidium into strontium. It can be used rocks from the Precambrian 4.5 billion years ago to the Cretaceous period about 50 million years classify time. For younger rocks other geochronological methods are preferable.

Thanks to the presence of stable reference isotope 86Sr, the Radiometric dating is based on the Isochronenmethode. This makes it less susceptible to estimating the initial concentration and reaches an accuracy of up to 5%.