Absolute dating radiocarbon dating. The development of accelerator mass spectrometry (AMS) dating, which allows a date to be obtained from a very small sample, has been very useful in this regard. Other radiometric dating techniques are available for earlier periods. One of the most widely used is potassium–argon dating (K–Ar dating). Potassium-40 is a radioactive isotope of potassium that decays into argon-40. The half-life of potassium-40 is 1.3 billion years, far longer than that of carbon-14, allowing much older samples to be dated. Potassium is common in rocks and minerals, allowing many samples of geochronological or archeological interest to be dated. Argon,
Index to Marine & Lacustrine Geological Samples JSP and an ArcIMS interface. Data selections can be downloaded in tab-delimited or shapefile form, depending on the interface used. Both WMS and WFS interfaces are also available. The Index was created in 1977 in response to a meeting of Curators of Marine Geological Samples, sponsored by the U.S. National Science Foundation. The Curators' group continues to meet every 2–3 years. Index to Marine & Lacustrine Geological Samples The Index to Marine & Lacustrine Geological Samples is a collaboration between twenty institutions and agencies that operate geological sample repositories. The purpose of the database is to help researchers locate sea