Isotope persisted down to the present because their rate of decay is so slow (e.g. uranium-238 and potassium-40). Post-primordial isotopes were created by cosmic ray bombardment as cosmogenic nuclides (e.g., tritium, carbon-14), or by the decay of a radioactive primordial isotope to a radioactive radiogenic nuclide daughter (e.g. uranium to radium). A few isotopes are naturally synthesized as nucleogenic nuclides, by some other natural nuclear reaction, such as when neutrons from natural nuclear fission are absorbed by another atom. As discussed above, only 80 elements have any stable isotopes, and 26 of these have only one stable isotope. Thus, about two-thirds
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