The 4th millennium BC saw major changes in human culture. It marks the beginning of the Bronze Age and of writing.
The city states of Sumer and the kingdom of Egypt are established and grow to prominence. Agriculture spreads widely across Eurasia. World population in the course of the millennium doubles, approximately from 7 to 14 million people.
3600 BC — Construction of the Ġgantija megalithic temple complex on the Island of Gozo, Malta: the world's oldest extant free-standing structures, and the world's oldest religious structures. (Dubious: see Göbekli Tepe)
3600–3200 BC — Construction of the first temple within the Mnajdra solar temple complex on Malta, containing "furniture" such as stone benches and tables, that set it apart from other European megalith constructions.
3600–3000 BC — Construction of the Ta' Ħaġrat and Kordin III temples on Malta.
Neolithic Chinese settlements. They produced silk and pottery (chiefly the Yangshao and the Lungshan cultures), wore hemp clothing, and domesticated pigs and dogs.
Vietnamese Bronze Age culture. The Đồng Đậu Culture, 4000-2500 BC, produced many wealthy bronze objects.
c. 4000 – 3000 BC — Austronesian peoples reach Formosa (Taiwan) having crossed 150KM from China using advanced maritime technology.
The climate was altered suddenly with severe impacts.
Plants buried in the Quelccaya Ice Cap in the Peruvian Andes demonstrate the climate had shifted suddenly and severely to capture the plants and preserve them until now.
A man trapped in an Alpine glacier ("Ötzi the Iceman") is frozen until his discovery in 1991.
Tree rings from Ireland and England show this was their driest period.
Ice core records showing the ratio of two oxygen isotopes retrieved from the ice fields atop Africa’s Mount Kilimanjaro, a proxy for atmospheric temperature at the time snow fell.
Major changes in plant pollen uncovered from lakebed cores in South America.