If the inhabitants of the earth of 30,000 years ago were the same as modern man where is their information they left for us to find?
Information on early humans is in the ground; such places are usually called 'archaeological sites'.
If they were not capable of leaving that iformation then they are not the same as modern man, we have planted the information.
This is of course silly. The fact that they did not leave information intended for later generations (as far as we can test) does not mean that they were incapable of doing so. It might just as well be that they felt that it was not necessary or that they in fact did leave time capsules but that they did not survive or that we do not recognize them. I for sure have no intention whatsoever to leave a time capsule; does that mean that I am not a 'modern man'?