There is mention of marriage and divorce by the Sumerians, the oldest known civilization. A cuneiform tablet circa 2000BC translates: For his pleasure, marriage. On thinking it over, divorce. This seems to say marriage had rights and legal status. Going back further, before the oldest known writings we have the graves Eridu. Some of the excavated graves contained couples, apparently buried at different times. These were apparently couples, perhaps spouses. Hard to be sure without writing, but I don't think it's too big a jump to say they were married. I'm unsure when they were dated, I don't have the book right here. I know the predate the first Sumerian cities by quite a bit, though. I think 4000-5000BC. Hopefully a Near East/Mesopatamian scholar can provide more details.