Oxides of group 2 were originally thought to be elements, not compounds.  These "elements" were called alkaline earths: "alkaline" because they're basic when added to water, and 'earth' because that's what they called oxides that they thought were elements.

The Group IA elements are called alkali because when they reacts with water they forms basic solutions like Na metal reacts with water and form NaOH a strong base.