Rubidium-strontium dating

Rubidium-strontium dating
Name	Rubidium–strontium dating
Type	Radiometric dating
Isotope	Rubidium-87 decaying to Strontium-87
Half-life	~4.88×10^10 years
Primary use	Geochronology, cosmochemistry

Rubidium-strontium dating is a radiometric dating method that exploits the beta decay of Rubidium-87 to Strontium-87 to determine the age of rocks, minerals, and meteorites. Developed and refined through collaborative work across institutions such as University of California, Berkeley, Carnegie Institution for Science, and Smithsonian Institution, the technique has been applied in studies linked to figures and events including Arthur Holmes, Alfred Wegener, Vine–Matthews–Morley hypothesis, Apollo 11, and Geochronology initiatives. Laboratories at Massachusetts Institute of Technology, Caltech, University of Cambridge, Max Planck Society, and NASA have advanced instrumentation and calibration standards used in this method.

Introduction

Rubidium-strontium dating uses the radioactive decay of Rubidium-87 (87Rb) to radiogenic Strontium-87 (87Sr) with a half-life comparable to geological time scales, providing ages for samples from contexts such as Precambrian, Phanerozoic, Cenozoic, and Mesozoic terrains as well as extraterrestrial materials returned by missions like Luna 16 and Apollo 11. The method is commonly applied in studies tied to institutions and persons such as United States Geological Survey, Geological Survey of Canada, Arthur Holmes, Clair Cameron Patterson, Harold Urey, and Victor Goldschmidt.

Principles and Theory

The theoretical basis rests on radioactive decay laws articulated by early workers associated with Royal Society, University of Oxford, University of Chicago, and researchers such as Ernest Rutherford and Bertram Boltwood. The decay equation N(t)=N0 e^{-λt} and the isochron approach were formalized in contexts involving collaborations among Columbia University, University of Göttingen, Scripps Institution of Oceanography, and researchers influenced by Alfred Wegener and James Hutton. Isochron theory employs samples with varying initial 87Sr/86Sr ratios so that a plot against 87Rb/86Sr yields a line whose slope corresponds to age, connecting to chronologies used in studies by Geological Society of America, American Geophysical Union, Royal Society of London, and geochronologists working with USGS mapping programs.

Methodology and Analytical Techniques

Sample selection, chemical separation, mass spectrometry, and data interpretation link laboratory workflows at Carnegie Institution for Science, Caltech, MIT, Max Planck Institute, and University of Tokyo with instrument vendors and standards endorsed by International Union of Geological Sciences and committees such as those from American Chemical Society and International Association of Geochemistry. Typical procedures include dissolution using acids in clean labs such as those at Lawrence Berkeley National Laboratory and ion-exchange chromatography to isolate strontium and rubidium; isotopic ratios 87Sr/86Sr and 87Rb/86Sr are measured by thermal ionization mass spectrometry (TIMS) or multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) in facilities like Vernadsky Institute and GEOMAR. Data reduction applies decay constants and calibration tied to standards developed through collaborations with National Institute of Standards and Technology, International Atomic Energy Agency, and researchers from Harvard University and University of California, Los Angeles.

Applications in Geology and Cosmochemistry

Rubidium-strontium dating has been applied to constrain ages of continental crust formation events, orogeny timings such as Himalayan orogeny studies, and to date metamorphic episodes in regions including the Canadian Shield, Shield of Brazil, and Scandinavian Shield. In sedimentary provenance and diagenesis work, laboratories affiliated with British Geological Survey and Geological Survey of India integrate Rb–Sr results with data from U-Pb dating, K–Ar dating, and Ar–Ar dating. Cosmochemical applications include absolute ages for lunar samples from Apollo program, meteorites such as the Allende meteorite, and constraints on solar system formation coordinated with institutions like NASA Johnson Space Center, European Space Agency, and researchers including Victor Goldschmidt and Clair Cameron Patterson.

Limitations and Sources of Error

Key limitations recognized by groups at USGS, British Geological Survey, Max Planck Society, and academic departments at University of Cambridge and ETH Zurich include open-system behavior, metamorphic resetting, metamorphic events tied to Plate tectonics and Wilson cycle processes, and inheritance of non-radiogenic strontium from crustal contamination. Analytical uncertainties can arise from mass fractionation in mass spectrometers produced by companies linked to Thermo Fisher Scientific and from inter-laboratory calibration differences addressed by committees at IAEA and NIST. Assumptions about initial 87Sr/86Sr are tested using isochron methods and cross-validated with other chronometers employed by teams at Caltech, MIT, Princeton University, and Yale University.

History and Development

The method traces conceptual roots to early 20th-century radioactive decay studies by Ernest Rutherford and to geochronological applications developed by Bertram Boltwood and advanced through the work of Arthur Holmes, Clair Cameron Patterson, and others at institutions like Carnegie Institution for Science and Caltech. The introduction of isochron techniques and improvements in mass spectrometry during the mid-20th century involved laboratories at University of Chicago, Harvard University, MIT, and Scripps Institution of Oceanography, and were influenced by large-scale scientific efforts such as postwar research funded by agencies like National Science Foundation and U.S. Office of Naval Research.

Notable Case Studies and Results

Notable applications include age determinations for the Allende meteorite and other chondrites analyzed at Smithsonian Institution and University of Arizona, Rb–Sr constraints on lunar basalts from the Apollo missions processed at NASA and Caltech, and crustal evolution studies of the Canadian Shield and Kaapvaal Craton undertaken by teams from Geological Survey of Canada and University of Witwatersrand. Integrative studies combining Rb–Sr with U–Pb geochronology, Sm–Nd dating, and Pb–Pb dating by consortia at GEOMAR, Max Planck Institute, University of Cambridge, and ETH Zurich have produced high-precision timelines relevant to debates involving Alfred Wegener-era continental reconstructions and modern tectonic syntheses presented at meetings of the Geological Society of America and American Geophysical Union.

Category:Geochronology