March 3, 2012

Bantu expansion damaged the Central African rainforests

Some 3000 years ago the sediments of the Congo river's mouth were suddenly altered in an unexpected way: it is the signature of the first forest agriculture, which implied opening patches of the rainforest, allowing weathering of the soil.

The researchers analyzed the cores for elements like hydrogen that leave distinctive signatures in sediment. These geochemical markers correspond with past precipitation levels, which influence weathering. They also examined ratios of aluminum and potassium, which indicate weathering intensity, because potassium is a highly mobile element whereas aluminum is one of the most immobile. As expected, the weathering patterns closely followed precipitation levels—that is, until about 3000 years ago. At that point, Bayon says, the pattern became completely different. The sediment appeared to have undergone intense chemical weathering, which the climate alone could not explain. So the team began suspecting another factor was responsible. 

Hat tip to Stone Pages' Archaeonews.


  1. Innovative way to date Bantu expansion in a low preservation environment for traditional artifacts.

  2. It is not obvious that such was the goal of the study but certainly it is yet another support for the mainstream datings of c. 1000 BCE.

    I'm not too familiar with the relevant archaeology behind that date but I see that the "3000 years ago" date pops up once and again where Bantu expansion or Bantu languages are dealt with, so it's not any new notion.

  3. The study is a step up from the pollen studies my friend used to do. Same conclusions are possible though.

  4. Though Bayon e.a. did interesting research and analysis, their interpretation is not to be accepted based on two major points.
    a) a consensus exists with strong data from terrestrial sites from Cameroon, through Gabon and in both Congos the deforestation evident from 3000 bp onwards was due to climatic reasons (very dry conditions compared to the previous period), and this deforestation - to simplify slightly - is synchronous where palaeo-environmental research was conducted, this pointing to a regional, perhaps global climatic episode;
    b) when this deforestation started to be felt or witnessed by the earliest villagers, they were then only located in southern Cameroon -none yet in Congo or along the Congo river - a slow but regular migration had set forth southwards. It is only after 2500 BP villages were settled on some stretches of the Congo river.
    Bayon et al did not take into account the data from archaeology and palaeo-environmental studies.

    1. Potentially interesting, thanks.

      Do you have any reference that would support your viewpoint?


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