The chemical term earths was historically applied to certain chemical substances, once thought to be elements, and this name was borrowed from one of the four classical elements of Plato. "Earths" later turned out to be chemical compounds, albeit difficult to concentrate, such as rare earths and alkaline earths.
Earths are metallic oxides, and the corresponding metals were classified into the corresponding groups: rare earth metals and alkaline earth metals.
Famous quotes containing the word earth:
“Perhaps all artists were, in a sense, housewives: tenders of the earth household.”
—Erica Jong (b. 1942)