First Calendar Ever. The earliest evidence of astronomical activity is an ishango bone with markings, thought to be a lunar calendar which dates back to around 20, 000 bc. Archaeologists believe the warren field calendar was created by hunter gatherers around 8,000 bc, making it the world's oldest calendar discovered to date by a significant.
It consisted of 12 months with 29 or 30 days. Our ancestors used the sun, the moon, and the stars to measure time and form the very first calendars (meaning register).