"A suddenly cold climate about 5,500 years ago coincided with the advent of ancient Chinese civilization, implying some relationship between the two events."

5,500 years ago is very close to the end of the previous Mayan age, and the beginning of this one (3114 BC).

Most archaeological news that catches my eye these days is associated with either 3000-3500 BC, or 10,000-12,000 BC. These were each eras of massive change.

"About 5,500 years ago, a global climate change occurred and the average temperature dropped by two to three degrees centigrade due to solar activity and the orbit of the earth... Weapons became popular funeral objects, which means that wars were common at that time. And then castles appeared. All of these are deemed as signs of emerging civilization, said archaeologists."