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:
“High treason, when it is resistance to tyranny here below, has its origin in, and is first committed by, the power that makes and forever re-creates man.”
—Henry David Thoreau (1817–1862)
“There are certain books in the world which every searcher for truth must know: the Bible, the Critique of Pure Reason, the Origin of Species, and Karl Marx’s Capital.”
—W.E.B. (William Edward Burghardt)
“The essence of morality is a questioning about morality; and the decisive move of human life is to use ceaselessly all light to look for the origin of the opposition between good and evil.”
—Georges Bataille (1897–1962)