In re "earth mothers", I had forgotten at the time that I wrote my post above that "[the earth] our mother, who supports our feet" is a concept that occurs in the one example I have seen of the "Invitation to Thanksgiving", a form of recitation that is used in the Handsome Lake religion of the Longhouse. The Handsome Lake religion is a re-formulation for changed conditions of older Seneca religion, so the phrase or concept might (or might not) be a part of older Seneca religious terminology. It might (or, again, it might not) be significant for establishing the history of this concept that the earth is not one of the "four beings", sun, moon, wind, and Thunderers, who are said to have brought the Creator's message to Handsome Lake (died 1815).
The same difficulties apply to this Seneca motif as to the phrase "grandmother and mother, the earth" that occurs in the rituals of the Oglala (in the translation I have seen). The question of whether the phrase itself is ancient or recent must be separated from the question of how the phrase has been re-interpreted by succeeding generations, and what factors, internal and external, have influenced those re-interpretations. Beyond that, there is the question of whether, if some "mother earth" concept is traditional to one or more of the nations, the "mother" concept in (say) a Libana song is the trational concept, a nontraditional concept fortuitously using the same words, or another re-interpretation, combining old and new.
Marymac90, I never thanked you for the kind words. Thanks!