4th millennium BC

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Millennia: 5th millennium BC - 4th millennium BC - 3rd millennium BC

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.

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Based on studies by glaciologist Lonnie Thompson (professor at Ohio State University and researcher with the Byrd Polar Research Center) [1] a number of indicators shows there was a global change in climate 5,200 years ago:

  • 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.
  • Record lowest levels of methane retrieved from ice cores from Greenland and Antarctica.
  • End of the Neolithic Subpluvial, start of desertification of Sahara (35th century BC). North Africa shifts from a habitable region to a barren desert.
  • Disastrous floods in Mesopotamian region.

  1. ^ Roberts, J: "History of the World.". Penguin, 1994.
  2. ^ Roberts, J: "History of the World.". Penguin, 1994.
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