Lore Fact:the collapse took a couple centuries (judging by not only the grimoire cards but also the dialogue overheard by the vendors at the tower) Lore fact :a group of awoken (early in post collapse) traveled back to Earth Lore fact: it has been several centuries since said collapse ,so any race starting in that location can be explained away ("you've been dead a long time ,"could cover a large time frame ,Bungie left it so vague on purpose.)