Geoscience Reference
In-Depth Information
diatomite were living close to the lake about 0.8
0.3 Ma ago and that once the lake
dried up, some of the stone tools were washed onto the now dry surface of the lake
during occasional sheet-floods. Elsewhere in northern and eastern Africa, Acheulian
occupation sites are invariably associated with the presence of freshwater lakes, rivers
or springs (Clark,
1980
), suggesting a close dependence on permanent sources of
water.
±
17.7 Conclusion
Prehistoric evidence of a former human presence in areas that are now too arid to
support much life is generally associated with other evidence from lake and river
sediments, fossil pollen grains and macrofossil remains that show that conditions
were wetter at those times. The archaeological record has the double advantage of
providing skeletal remains (that can be dated and analysed using stable isotopes to
determine past diet in the case of Holocene remains), as well as associated stone
tool assemblages. Determining the functions of prehistoric tools is not always easy,
and current systems of stone tool classification are based on size, shape and overall
morphology, rather than function, although studies of microwear and residues left on
the cutting edges of certain tools are throwing some light on prehistoric tool-use and
function. In the absence of other means of dating, both stone tool assemblages and
skeletal remains can be used to provide a relative chronology of the deposits in which
they occur.
The late Miocene and Pliocene hominids are confined to Africa and are now well
dated. The oldest known stone tools come from the Gona tributary valley to the Middle
Awash Valley of the Ethiopian Afar Rift and date to around 2.5Ma. These pebble tools,
or Oldowan tools, were used for more than 1 million years before being succeeded by
Acheulian hand-axes and cleavers. The Oldowan and Acheulian together comprise
the Early Stone Age, or Lower Palaeolithic. Oldowan and Acheulian tools are found
across Eurasia, and indicate periodic movement out of Africa by
Homo erectus/Homo
ergaster
via the Levantine Corridor during times when the climate was wetter. The
Middle Palaeolithic/Middle Stone Age began about 500 ka in southern Africa but
may not have originated until 300 ka further north. One hallmark of the Middle Stone
Age was the use of hafting stone projectile points made from previously shaped cores.
Soon after 50 ka, the Middle Stone Age gave way to the Later Stone Age, or Upper
Palaeolithic. This was a time of great regional diversity in stone tool-making and of
the proliferation in certain localities of rock art, sculpture and the manufacture of
stone artefacts of great beauty, no doubt used for trade and for establishing social
networks.
A contentious and still unresolved issue concerns the possible role of prehistoric
humans in faunal extinctions, with some evidence pointing to climate change as a
key factor, some suggesting over-predation from hunting and some indicating habitat
