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:
“There is not much sense in suffering, since drugs can be given for pain, itching, and other discomforts. The belief has long died that suffering here on earth will be rewarded in heaven. Suffering has lost its meaning.”
—Elisabeth Kübler-Ross (b. 1926)