Earth (historical chemistry)

These rare-earth oxides are used as tracers to determine which parts of a watershed are eroding. Clockwise from top center: praseodymium, cerium, lanthanum, neodymium, samarium, and gadolinium.

These rare-earth oxides are used as tracers to determine which parts of a watershed are eroding. Clockwise from top center: praseodymium, cerium, lanthanum, neodymium, samarium, and gadolinium.

Earths were defined by the Ancient Greeks as "materials that could not be changed further by the sources of heat then available".<ref name=":0">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Several oxides were thought to be earths, such as aluminum oxide and magnesium oxide.<ref name=":0" /> It was not discovered until 1808 that these weren't elements but metallic oxides.<ref name=":0" /><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

See also

• Rare earth metals
• Alkaline earth metals

References

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