Island 35 Mastodon Island 35 Mastodon The Island 35 Mastodon was discovered on Island No. 35 of the Mississippi River in Tipton County, Tennessee, United States. In 1900, a Pleistocene mastodon skeleton was excavated approximately east of Reverie, Tennessee and southeast of Wilson, Arkansas. In 1957 the site was reported as destroyed. Mastodons are members of the prehistoric, extinct genus "Mammut". They resemble modern elephants. Native to North America, they are said to have lived on the North American continent from almost 4 million years ago, in the Pliocene Epoch, until their eventual disappearance about 10,000 years ago. In 1900, archaeologist James K.
Extinct radionuclide 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 years. Short-lived radioisotopes that are found in nature are continuously generated or replenished by natural processes, such as cosmic rays (cosmogenic nuclides), background radiation, or the decay chain or spontaneous fission of very long-lived isotopes such as uranium or thorium. Short-lived isotopes that are not generated or replenished by natural processes are not