The 4th millennium BC saw major changes in human culture. It marked the beginning of the Bronze Age and the invention of writing, which played a major role in starting recorded history.
The city states of Sumer and the kingdom of Egypt were established and grew to prominence. Agriculture spread widely across Eurasia. World population in the course of the millennium doubled, 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 unburied free-standing structures, and the world's oldest religious structures. (See Göbekli Tepe for older, buried religious structures.)
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.
The cuneiform script proper emerges from pictographic proto-writing in the later 4th millennium. Mesopotamia's "proto-literate" period spans the 35th to 32nd centuries. The first documents unequivocally written in the Sumerian language date to the 31st century, found at Jemdet Nasr.
Naqada culture on the Nile, 4000 BC–3000 BC. First hieroglyphs appear thus far around 3500 BC as found on labels in a ruler's tomb at Abydos.
Mande Peoples start developing a series of agricultural and complex urbanized sites, establishing the foundations of the latter Ghana Empire as evident per Tichitt; Oualatta; and the supposed archaeological site of Koumbi-Saleh (However, there is dispute as to whether the site deemed 'Koumbi Saleh' is in fact the legendary city for it doesn't feature the palace complex, and carbon dating results point to the city being built at around the 9th century at the earliest).
Neolithic Chinese settlements. They produced silk and pottery (chiefly the Yangshao and the Lungshan cultures), wore hemp clothing, and domesticated pigs and dogs.
According to calculations of Aryabhata (6th century), the HinduKali Yuga began at midnight (00:00) on 18 February 3102 BC. Consequently, Aryabhata dates the events of the Mahabharata to around 3137 BC.
^Thompson, L. G.; Mosley-Thompson, E.; Brecher, H.; Davis, M.; León, B.; Les, D.; Lin, P. -N.; Mashiotta, T.; Mountain, K. (2006). "Inaugural Article: Abrupt tropical climate change: Past and present". Proceedings of the National Academy of Sciences103 (28): 10536. Bibcode:2006PNAS..10310536T. doi:10.1073/pnas.0603900103.edit