Man has been on earth for millions of years. Recorded history has covered only a few thousands of these years. Archeologists can account for a few thousand more. If you think about it, that leaves time for numerous rises and falls of advanced cultures, sufficient time that no sign of their existence would be recognizable today. Some of these near extinctions were probably triggered by worldwide events. These events in a few hundred years, if remembered at all, were only myths and legends. I t