Why are alkaline-earth metals called alkaline earths?

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A color-coded periodic table of the elements displays each element's symbol and atomic number, with categories such as alkali metals, noble gases, halogens, transition metals, and actinoid elements distinguished by different background colors. — alkaline-earth metal Modern version of the periodic table of the elements (printable).

Before the 19th century, the term "earths" was used to describe substances that were nonmetallic, insoluble in water, and resistant to heat. Among these, substances like lime (calcium oxide) were observed to resemble alkalies—such as soda ash and potash—in their chemical behavior. Consequently, these specific substances were designated as "alkaline earths" to distinguish them from other earths, such as alumina and the rare earths.1

By the early 1800s, it was discovered that these earths were not elements themselves but were actually oxides—compounds consisting of a metal and oxygen. The metals that formed these alkaline-earth oxides subsequently became known as the alkaline-earth metals, a classification that remains in Group 2 of the periodic table today.1