It has long been known that the so-called Bradshaw rock
paintings of the Kimberley region are more ancient than the Wandjina
art in the same area.
Most rock art specialists have come to consider them as being
of early to mid-Holocene age, although there is always the
possibility that these detailed and often very dynamic
red paintings belong to an art tradition that may have begun
in the late Pleistocene.
Scientific evidence has just been presented that Bradshaw figures
were already painted more than 17 000 years ago.
Robert (Bert) Roberts of La Trobe University, together with
eleven co-authors, has published new findings in the 12 June
1997 issue of Nature that seem to indicate a Pleistocene age
for at least some of this stunning rock art.
If correct, these results would make the Bradshaws the oldest
known detailed depictions of human figures in the world.
Dr Roberts, who has produced important archaeological data from
northern Australia before, used optically stimulated luminescence
(OSL) in an attempt to determine how long ago quartz grains
from wasp nests were last exposed to light.
He analysed samples from seven different wasp nests, some covering
paint residues, others occurring near paintings.
The theory is that mud-dauber wasps who occasionally construct
their nests over rock art exposed tiny sand grains to daylight
when they collected mud and carried it to the rockshelters.
This ‘resets’ the luminescence ‘clock’ in the quartz, allowing
the mineral to freshly accumulate electrons within crystal lattices,
which indicates the amount of radiation the quartz grains were
exposed to while enclosed in the wasp nest structures.
After determining background radiation at the site for
calibration, the energy trapped in the quartz grains is measured,
providing an indication of when the grains were supposedly
last subjected to light radiation.
Nine samples were analysed from successive layers of just one nest,
DR6, in order to compare the results.
The sample from the surface gave an age estimate of 110 years,
then followed five samples of between 250 and 310 years, and
the three innermost were 590 to 610 years.
Two of these samples were prepared as single-aliquot additive-dose,
the others as multiple-aliquot samples.
The former matched the results of the latter in both cases, and
the age estimates are in sequence.
They are interpreted as indicating that the nest was constructed
in two phases: the more recent structure was attached to the
remnants of an earlier nest, something the wasps are
commonly observed to do.
The core of a nest partly covering an anthropomorphous rock
painting produced an age estimate of c. 17 500 years, indicating
that the underlying human figure should be older than this date.
Another nest, not covering rock art, was dated at c. 23 800 years.
The results are interpreted as indicating that human figures
were painted at least 17 500 years ago in the Kimberley.
This announcement coincided with the publication of a paper in
the May 1997 issue of Rock Art Research, in which Dr Alan Watchman
and three colleagues reported radiocarbon dates obtained from several
‘Bradshaw’ paintings.
The carbon for these analyses was extracted from accretions directly
associated with paint residue layers.
A tassel-decorated anthropomorph yielded three very similar dates,
of about 1430-1490 years BP, a large ‘naturalistic’ animal figure
with infill produced one date of about 3140 years, and a ‘cane
Bradshaw’ figure seems to be about 3880 years old.
One of the dates from the first figure comes from under the
paint layer, and the close clustering of the three results
implies that these are fairly valid.
Bradshaws would therefore seem to be a Holocene phenomenon,
as had been widely assumed.
It is possible that this particular genre of painting human
figures extended well into the Pleistocene, but such a long
duration of so distinctive a style seems rather unlikely.
There are a number of possibilities to explain the very early date
Roberts et al. produced from just one anthropomorph: it
may not be a Bradshaw figure, but belong to some earlier
artistic convention; or the dating is simply wrong.
While this dating work is technically superior to the earlier
attempt at the infamous Jinmium site, there are still some
considerations regarding its reliability.
Reliance on a single ‘date’ is always risky, and more
such results would be most desirable.
One of the questions to consider is whether the wasps
necessarily exposed the quartz grains to adequate light to
re-set the clock, and how much light is actually required to do so.
It seems perfectly possible that wasps were working in the dusk,
and that the mud came from deep and dark soaks that experienced
very little exposure to light.
How did the wasps carry the mud in flight, and were the grains
in the core of each mud cargo exposed to sufficient light?
The answers may not be so clear-cut and further research into
these matters may still change perceptions about these results.
For the time being, Dr Robert’s result is spectacular but provisional,
and should certainly not be used further in the formation of all
sorts of derivative archaeological or art historical hypotheses.
Robert G. Bednarik