Have you heard about the Ishango bone? The ancient baboon bone covered in incisions was discovered in the 1960’s on the shore of a lake in the current Democratic Republic of the Congo. It has been dated to somewhere between 20,000 B.C. and 25,000 B.C. Similar bones have been found in other locations in Africa and in Europe, with the oldest known bone with similar incisions dating to 37,000 B.C.
The markings, done in intervals of 28 or 29, were “assumed” to be agricultural calendars or even calendars tracking the phases of the moon.