publiusPlutonium-244 has a long enough half-life that it has been found in cosmic dust, generally thought to be from supernova remnants. It's been used in attempts to determine the chronology of seabed sediment deposition. As far as practical chemistry is concerned, however, it's strictly a man-made element.
GNU social JP is a social network, courtesy of GNU social JP管理人. It runs on GNU social, version 2.0.2-dev, available under the GNU Affero General Public License.
All GNU social JP content and data are available under the Creative Commons Attribution 3.0 license.