Here is a link with more info on it: http://en.wikipedia.org/wiki/Cucuteni-Trypillian_culture
* but then "comprehensive" means little more than "a thorough overview of basic Western European history starting with the ancient Greeks". It's not hard to imagine a history curriculum that spends more time on cultures before that.
As far as this specific culture is concerned, however, note the article says very little about it was known until 1972 and even after that, the knowledge was confined to Bulgaria and Romania, so it's at least somewhat understandable that it didn't make it into 5th grade curricula until after the Iron Curtain came down (by which time I was in 9th grade, btw).
I was being sneaky a little but the point was that when it come to "the oldest artifact...X", the "earliest...Y" it should be something that is taught and studied world-wide.
The downside is that we didn't study much American history, or at least not as much as I would have liked.
Edit: For benefit of our international readers: this is sort of like including a Golden Retriever (dog breed) in the lineup of 25 beautiful cats.
Certainly a Golden Retriever is never a cat - about that I am not confused.