E's and o's get doubled in English regularly, but a's typically do not. The words aardvark and aardwolf are two exceptions. Both come from early Afrikaans (note the a's), in which aarde means "earth."
Afrikaans, one of the official languages of South Africa, is a language developed from 17th century Dutch. Afrikaans has changed over the centuries and the Afrikaans word that English aardvark is based on is no longer in use. In early Afrikaans there was competition between the standard Dutch aarde and the North/South Holland form erd(e), and in the creature's name the latter won out: the modern Afrikaans word for an aardvark is erdvark. Afrikaans still has both of those forms, though, as words with different senses: erd means "earth, clay," and aarde means "Earth"—the planet.