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Nature Communications published an article in May, 2013 that just now caught my eye. The paper’s title, “Development of Middle Stone Age innovation linked to rapid climate change,” lays down a solid understanding of what the authors found… The one line summary of the article is: the authors observed that very abrupt changes in rainfall in South Africa, about 40,000 – 80,000 years ago, correlated with the development of new technologies.

Stone tools known as bifacial points recovered from Blombos Cave, South Africa. They were made during the Middle Stone Age, about 75,000 years ago, by anatomically modern humans. Scale bar: 1 cm (0.4 inches). CREDIT: Courtesy of Christopher Henshilwood, University of the Witwatersrand

Stone tools known as bifacial points recovered from Blombos Cave, South Africa. They were made during the Middle Stone Age, about 75,000 years ago, by anatomically modern humans. Scale bar: 1 cm (0.4 inches).
CREDIT: Courtesy of Christopher Henshilwood, University of the Witwatersrand

The global climate of last million years varied between glacial and interglacial periods. These changes occurred about every 100,000 years. But within these long-term periods there have been shorter blips of climate changes, sometimes happening in the span of just a few decades. During these short blips, variations of up to 10ºC in the average temperature of the polar regions are caused by changes in the Atlantic ocean circulation, which ultimately affected rainfall in southern Africa.

Signs of modern human culture - symbolic artifacts from around 75,000 years ago unearthed from Still Bay at Blombos Cave, South Africa: a) bifacial foliate point, b) bone tool, c) engraved ochre, d) shell beads, e) engraved bone. Credit: Christopher Henshilwood

Signs of modern human culture – symbolic artifacts from around 75,000 years ago unearthed from Still Bay at Blombos Cave, South Africa: a) bifacial foliate point, b) bone tool, c) engraved ochre, d) shell beads, e) engraved bone. Credit: Christopher Henshilwood

By analyzing river delta deposits, the researchers of this paper have pieced together how rainfall patterns varied in southern Africa over the last 100,000 years. Every millimeter of sediment core corresponds to 25 years of sedimentation. The ratio of iron to potassium in the layers is a record of the sediment carried by rivers and of the rainfall throughout the period. With that the authors were able to see patterns in the climate… As the South African climate changed rapidly towards more humid conditions, the northern sub-Saharan Africa experienced widespread droughts, and the Northern Hemisphere entered phases of extreme cooling.

The reconstruction of the rainfall over 100,000 years shows a series of spikes that occurred between 40,000 and 80,000 years ago. These spikes show rainfall levels rising sharply over just a few decades, and falling off again soon afterwards, in a matter of centuries. The climate changes coincided with abrupt emergence of material culture and modern behaviour such as the beginnings of symbolic expression, the making of tools from stone and bone, jewellery and the first agricultural settlements. And in turn, the end of certain stone tool industries of the period coincides with the onset of a new, drier climate.

Climate change during the Middle Stone Age in Southeast Africa

Climate change during the Middle Stone Age in Southeast Africa

The findings confirm one of the principal models of Palaeolithic cultural evolution, which correlates technological innovation with the adoption of new refuges and with a resulting increase in population and social networks.

 

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