Question

what was the natural changed that occurred around 9000 bc?

Answer 1

The 9th millennium BC marks the beginning  of the Neolithic period. [NP] Agriculture spread throughout the Fertile Crescent and use of pottery became more widespread. Larger settlements like Jericho arose along salt and flint trade routes. Northern Eurasia was resettled as the glaciers of the last glacial maximum retreated. World population was at a few million people, likely below 5 million..