How do you think it would have occurred without composite materials?
I don't necessarily think that it would or could (
or wouldn't or couldn't) have, at all. No way for me to extend myself that far, and no way for me to assume that we could rely on recognizing potential evidence after unknown spans of time.
If such people existed, then was everyone on our planet similar in development? Or was it a closed society making use of resources only for themselves? Had they perhaps been in contact with others who'd lived here even earlier, before their own journey into space? Did they have space-developed technology that we (our current selves, today) couldn't begin to conceive of?
It becomes very difficult to make assumptions without tripping yourself up.
What do you think?