Cultures and maybe even civilization are not limited to humans, even. Other smart species do seem to be able to transmit knowledge fr one generation to the next, sometimes for reasons not obvious to us. I am reminded of the habit of some West African chimpanzees to throw stones, almost ritualistically, at a particular tree. If we are talking about advanced civilizations, anything close to the industrial level, then the odds are quite good that they would have been found by now. Samples of ice accumulated over millennia in Greenland and Antarctica preserve records of atmospheric conditions, including man-made pollutants. Similarly, the scars made by industrial civilization in its extraction of resources are readily visible. Had there been even a civilization comparable to 18th century Europe, say, some time in human history, this civilization would have been revealed by now.