Earth

The term earths was historically applied to certain substances that were once thought to be elements, and this name was borrowed from one of the four classical elements of Plato^{[citation needed]} the other three being air, water, and fire. "Earths" were later found to be metallic oxides,^[1] and the corresponding metals were classified into the corresponding groups; rare earth metals and alkaline earth metals.^{[citation needed]}

References

↑ "Alkaline-earth metal". https://www.britannica.com/science/alkaline-earth-metal. ""By the early 1800s it became clear that the earths, formerly considered to be elements, were oxides, compounds of a metal and oxygen.""

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[1] "Alkaline-earth metal". https://www.britannica.com/science/alkaline-earth-metal. ""By the early 1800s it became clear that the earths, formerly considered to be elements, were oxides, compounds of a metal and oxygen.""