With all respect, Piper, I think you’re overreacting.
What’s a little over-rection amongst friends? 
Teff (an uniquely Eritrean/Ethiopian grain) is a major staple for Eritreans/Ethiopians, but we also grow corn, wheat, etc… Mainly, we grow what can grow in our climate (rocky, high altitude, erratic rain patterns). I don’t know if this can help but a month ago it was discovered that the ‘Oldest’ African settlement was found in Eritrea. It was a agricultural community that was found close to the capital of Asmara.
Also here is crop zones for both countries listing what grows and where (maybe this can help): 1, 2.
It doesn’t look to me like any grain crop fits the pattern of “the Semitic language [spread] with the domestication of [that grain].” Notice that the maps in the pictures given by efrem are for the modern spread of these grains. Maize (i.e., corn) is a New World plant and thus didn’t reach Ethiopia and Eritrea until after the time of Columbus. Teff is the best known grain of Eritrea/Ethiopia (that’s what the injera you eat at Ethiopian restaurants is made of), but it doesn’t seem to have spread beyond those countries. I can’t think of any grain crop whose spread matches that of the Semites or of the Afro-Asiatics.
Well, I understood his POV in the OP restriction on “religious posters” to mean “I want to eliminate religion-based commentary on language origins” because "everybody knows that they originated with the descendants of Noah’s three sons…
Certainly I can spout off on what a literalist interpretation of Scripture would say, and it would be totally useless to the glottochronological question at hand. So I put on my “not a religious poster at the moment” hat* and answered as best I could from my knowledge in linguistics (which is not overly deep).
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