Origin
Rare earth elements are heavier than iron and thus are produced by supernova nucleosynthesis or the s-process in asymptotic giant branch stars. In nature, spontaneous fission of uranium-238 produces trace amounts of radioactive promethium, but most promethium is synthetically produced in nuclear reactors.
Rare earth elements change through time in small quantities (ppm, parts per million), so their proportion can be used for geochronology and dating fossils.
Read more about this topic: Rare Earth Element
Famous quotes containing the word origin:
“All good poetry is the spontaneous overflow of powerful feelings: it takes its origin from emotion recollected in tranquillity.”
—William Wordsworth (1770–1850)
“For, though the origin of most of our words is forgotten, each word was at first a stroke of genius, and obtained currency, because for the moment it symbolized the world to the first speaker and to the hearer. The etymologist finds the deadest word to have been once a brilliant picture.”
—Ralph Waldo Emerson (1803–1882)
“Art is good when it springs from necessity. This kind of origin is the guarantee of its value; there is no other.”
—Neal Cassady (1926–1968)