It really doesn't have much to do with no presence of oxygen (directly). It's a fact that once certain heterotrophs learned how to produce its own food, then prokaryotic autotrophs were formed (big example is cyanobacteria). So if you remember that, I think that'll be sufficient enough for the DAT. I doubt they'll dig much deeper about theories of origin. I'd probably go as far as to say that it's safe to know the Oparin and Haldane Theory (that simple molecules were able to be formed without the presence of oxygen) and that Stanely Miller confirmed their findings. That's probably the worst of it, and it's not that bad...
