It is thought by Old Earth Creationists and evolutionists that during the 6th millennium BC many environments shifted around the world, triggering a change in subsistence patterns. Some historians allege that Hunter-gatherers in the Middle East begin to shift towards sedentary horticulture and early intensive agriculture. Young Earth Creationists, believing that the Earth is approximately 6,000 years old, do not believe that the 6th millennium BC took place at all.