In addition to the crater in the Iraq Marshes, there are also meteor craters in Argentina that date to around that same 4,000 ya period. I believe they were separated by about 200 years which fits with other world crises. Given Russia’s recent air burst, imagine what a mess would be caused by meteors/asteroids leaving craters several miles in diameter. The chart earlier on this site shows a definite temperature drop about 4,000 ya or slightly earlier.
I didn’t repost anything about the Iraq crater, but should have at least linked a topic or two that pertain to it. Maybe tomorrow. (yawn, stretch)