Simplify the following text for a Grade 10 native English-speaking person.
Original: The calendar circle correlation with Orion 's belt occurred between 6400 BC and 4900 BC , matching the radio-carbon dating of campfires around the circle .
Simplified: The last minimum of Orion 's belt occurred between 6400 BC and 4900 BC , matching the radio-carbon dating of campfires around the circle . .