Our site is using cookies to record anonymous visitor statistics and enhance your user experience.   OK | Find out more

Natural Environment Research Council Home
Skip to content

EFCHED

Shedding light on modern humans in Africa

Anatomically modern humans are thought to have emerged in southern or eastern Africa between 150ka and 200ka, though it is not until about 65ka years that they dispersed from Africa to other parts of the world, including Europe.

Excavations in the Kenyan Rift Valley. Image: G DullerThis EFCHED project used luminescence dating to extend the chronology of African archaeological sites back into this period between 200ka and 65ka. This is at the limit of current luminescence dating methods, so we needed to develop new measurement procedures.

We applied these new procedures to materials from a transect of sites from the Cape Coast of South Africa, through Zambia and into Kenya, following possible northward migration routes.

For the South African sites, which are found in caves along the coast, we measured luminescence signals from many thousands of individual sand grains to determine their age. These ages indicate that the occupation of these sites is influenced by global changes in sea level over the last 140ka.

Some of our major findings

It has been known for many years that archaeological sites in Africa contain records that are central to our understanding of the evolution of modern humans (Homo sapiens).

Because of the fragmentary nature and wide geographical spread of these records, methods for accurately dating them are essential.

Radiocarbon dating is limited to the last 40ka, too young to be useful for this study. Potassium-argon (K-Ar) or argon-argon (Ar-Ar) dating are only applicable to volcanic deposits, which occur in parts of eastern Africa, but are entirely absent from southern Africa. Luminescence dating is well suited to filling the gap between these two methods.

The technique uses the light emitted by minerals following exposure to radioactivity. This luminescence signal can be used as the basis for absolute dating.

In this project, luminescence was applied to the grains of quartz making up the sediments found at archaeological sites.

Excavation at Die Kelders, South Africa. Image: G Duller

At Blombos, in South Africa, the technique showed that the sedimentary sequence extends back to 140ka, though human occupation has been episodic, with long periods when the cave entrance appears to have been blocked by a large dune.

At this site, the use of luminescence measurements on single sand-sized grains has been essential in establishing an accurate chronology. This has shown that engraved ochre and shell beads at the site are over 70ka old, making them some of the earliest evidence for behavioural modernity in Homo sapiens.

In the Luangwa Valley of Zambia the archaeological finds occur in deposits laid down by the River Luangwa. These deposits have also been analysed using luminescence.

For young materials, the results demonstrate good agreement between radiocarbon and luminescence dates. However, the natural environmental radioactivity is approximately two to three times greater here than that in the South African cave sites. The effect is that the luminescence signal reaches its maximum level two to three times faster, reducing the time over which the method can be used.

Researchers at the University of Wales, Aberystwyth, have developed novel methods based on isothermal thermoluminescence signals from quartz to extend the age range over which the method can be applied, and this is being tested against independent chronological techniques.

The Kenyan Rift Valley also has high levels of natural radioactivity, as much as six times higher than those encountered in South Africa.

Additionally the luminescence properties of the quartz found here are unusual, as they are derived from the volcanic materials that are common in this part of East Africa. Our research has improved our understanding of the nature of this unusual quartz, and we developed methods for its analysis.

This project has successfully applied existing methods to yield accurate luminescence ages for some key Middle Stone Age archaeological sites. It has also spurred the development of novel luminescence methods that will be of value in future dating studies.

This summary was compiled by Geoff Duller. David Thomas (Oxford) is the PI for this project entitled "Chronology, adaptation and environment of the Middle Palaeolithic in Northern Africa: Implications for the dispersal of anatomically modern humans."

The research was led by Geoff Duller and undertaken at the University of Wales, Aberystwyth, in collaboration with:

Die Kelders and Blombos, South Africa - Graham Avery (Iziko South African Museum, Cape Town), Chris Henshilwood (University of Bergen), Zenobia Jacobs (University of Wollongong), Sumiko Tsukamoto and Ann Wintle (University of Wales, Aberystwyth).

Luangwa Valley, Zambia - Larry Barham (University of Liverpool), Mayank Jain (University of Wales, Aberystwyth and Risų National Laboratory), Sumiko Tsukamoto and Ann Wintle (University of Wales, Aberystwyth).

Rift Valley, Kenya - Stan Ambrose (University of Illinois), Jeong-Heon Choi (Korean Basic Science Institute).