Final answer:
According to Alexander Marshack's studies, the world's oldest calendar may have existed between c. 1070-713 BCE, as evidenced by bone artifacts with markings corresponding to lunar cycles and celestial events.
Step-by-step explanation:
Alexander Marshack, an American archaeologist, studied ancient artifacts and proposed that the world's oldest calendar may have existed between c. 1070-713 BCE. Marshack's research focused on bone artifacts found in Europe and Africa, which had markings that corresponded to lunar cycles and celestial events. These findings suggest that early humans were capable of tracking time and possibly using calendars much earlier than previously believed, providing insights into ancient civilizations' understanding of time and astronomy.