Mastodon Mastodon Mastodons (Greek: μαστός "breast" and ὀδούς, "tooth") are any species of extinct proboscideans in the genus Mammut (family Mammutidae), distantly related to elephants, that inhabited North and Central America during the late Miocene or late Pliocene up to their extinction at the end of the Pleistocene 10,000 to 11,000 years ago. Mastodons lived in herds and were predominantly forest dwelling animals that fed on a mixed diet obtained by browsing and grazing with a seasonal preference for browsing, similar to living elephants. "M. americanum", the American mastodon, is the youngest and best-known species of the genus. They disappeared from
Extinct radionuclide long half-lives. A partial list of radionuclides not found on Earth, but for which decay products are present: Notable isotopes with shorter lives still being produced on Earth include: Radioisotopes with half-lives shorter than one million years are also produced: for example, carbon-14 by cosmic ray production in the atmosphere (half-life 5730 years). Extinct radionuclide An extinct radionuclide is a radionuclide that was formed by nucleosynthesis before the formation of the Solar System, about 4.6 billion years ago, and incorporated into it, but has since decayed to virtually zero abundance, due to having a half-life shorter than about 100 million