THERE is no doubt that Jinmium is an ancient place. At the physical heart of
the site, located just inside the western border of Australia’s wild Northern
Territory, is a stone monolith rising 40 metres above the sandy floodplain.
Surrounding this impressive hunk of sandstone are smaller, but still enormous
boulders, poised like patient attendants. The arrangement of the stones is
natural, but what has been carved and painted on them is not.
The layers of rock art covering the monolith and its companions betray
Jinmium as an ancient cultural centre. Recently painted spirits and other
mysterious figures lie over earlier images of kangaroos, goannas, and other
animals. And beneath all these weathered images are nearly ten thousand carved
circular engravings, known as cupules.
When Richard Fullagar, an archaeologist with the Australian Museum in Sydney,
first saw Jinmium he guessed that it would reveal important details about the
lives of some of Australia’s earliest settlers. Still, he could never have
predicted the media frenzy and scientific furore that erupted when he and his
colleagues first told the world of their discoveries. “I was staggered,” recalls
Fullagar, who says the response, both local and international, was swift and
negative. The cause of the hullabaloo was the estimate made by Fullagar and his
colleagues of just how long humans have been visiting Jinmium.
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Fullagar, David Price and Lesley Head of the University of Wollongong and
Paul Taçon of the Australian Museum say that stone tools at Jinmium could
date back 176 000 years and its rock art 75 000 years. If true, this means the
team has pushed back the date for the settlement of Australia by about 100 000
years, and added an extra dimension to the long-standing controversy over the
origin of modern humans. The researchers could also have identified the oldest
known art in the world. These dates are stunning and to some scientists,
outlandish. “The ideas were considered so outrageous that a few very silly
academics were even saying the paper shouldn’t be published,” says Fullagar. “I
find it utterly outrageous.”
There are at least two reasons why the team’s results raised the hackles of
their colleagues. First, the dates are controversial: a fact the team freely
admits. Secondly, is the way the results emerged: not at a scientific meeting or
in the journal Antiquity, where they finally appear this week, but in a
newspaper.
Fullagar and his colleagues had always intended to announce the results just
before they appeared in Antiquity, in deference to the Aboriginal community
around Jinmium. But a spate of bad luck forced them to bring their plans
forward. Without the researchers’ knowledge, the Australian Museum announced to
the media in September that “exciting finds from Australia’s oldest
archaeological deposits, rock art sites and cultural landscapes” would be
presented at a lecture in November.
For inquisitive news reporters, such an announcement is like a red rag to a
bull. The researchers soon realised they could not stop the story leaking out
bit by bit and that they were in danger of breaking their promise that an
Aboriginal spokesperson would announce the results. “If we’d let it out in dribs
and drabs, both we and the Aboriginal community would have lost control of the
information,” says Fullagar. To keep the initiative, and with the full knowledge
of the editor of Antiquity, Cambridge University archaeologist Christopher
Chippindale, they decided to run with a full story in the Sydney Morning
Herald.
Then the trouble really started. The researchers, not to mention Chippindale,
found themselves in a passion-packed dispute. Criticism ranged from charges that
they had breached scientific protocol to accusations that they were mere
publicity seekers. Competition between Australian newspapers helped to keep the
fur flying.
This week, with the paper finally published, the debate should return to
Jinmium itself where, since 1992, archaeologists have unearthed layers of
sediment containing tools, bone and charcoal. Fullagar, Head and Price dated the
sediments in which such artefacts were found at between 116 000 and 176 000
years old. They also conclude that people at Jinmium were engaged in artistic
activity early on. Ochre, the iron-oxide based pigment, first appears in
sediment dated to between 75 000 and 116 000 years of age.
Nearby, a sandstone fragment with characteristic pit marks was found in
sediments between 58 000 and 75 000 years old. Taçon, a rock art expert,
concludes that the fragment fell from the cupule-covered wall of a rock shelter
in the site’s central outcrop. And starch grains found in association with 60
000 year-old pounding tools suggest that around this time, inhabitants processed
plant food, probably tubers. All up, the findings indicate that people were
living a rich life at the site much longer ago than most archaeologists had
suspected.
Before the significance of these findings can be properly gauged, however,
the teams’ dating expert, Price, must convince sceptics that the ages he
assigned to the sediments are solid (see Box). He used a comparatively new and
controversial method called thermoluminescence. Yet even advocates of the
technique, such as Bert Roberts, a geomorphologist at La Trobe University in
Melbourne, argue that the ancient bedrock at Jinmium crumbles easily and could
have contaminated layers of sediment, so giving them an older age than
expected.
“Jinmium has got a lot of decayed rubble in the ground,” says Roberts. “So my
concern with the Jinmium stuff is that the accuracy was woeful, regardless of
the precision [of Price’s work].” Roberts is about to begin dating samples from
the site using a luminescence method which he says will side-step this
difficulty and date the sediments much more accurately.
So what if Roberts finds that the Jinmium dates are accurate? What are the
implications? For one area of human capability—art—the implications
are revolutionary. For much of this century, the ability of humans to create
visual symbols was thought to have begun in Europe between 35 000 and 40 000
years ago. Both assumptions are now being challenged, according to Paul Bahn, a
freelance archaeologist based in Hull, England.
Recent finds in the Middle East, India and Australia show that Europe was not
the only place where art developed. And the date for the first art is also now
in question. “If the Jinmium dates are valid, and that’s a big `if’, it will
take rock art back to about 75 000 years ago,” says Bahn.
Ageing arrival
Jinmium could also have implications for the date humans first arrived in
Australia. Chippindale says that since March 1995 Antiquity has published three
papers that make good cases for the first settlement of the island at three
different dates: about 40 000 years ago, 60 000 years ago, and now well over 100
000 years ago. “All one can say is that for thirty years now, the credible dates
for the settlement of Australia have been getting older and older,” says
Chippindale.
Certainly, indirect evidence of human activity in the region so long ago has
been found in core samples taken from sediments around Australia and Indonesia.
Dating of charcoal and pollen in the cores suggests that people have been
setting fire to the landscape for more than 100 000 years.
In 1981, the late Gurdip Singh of the Australian National University (ANU) in
Canberra reported a dramatic change about 125 000 years ago, with a shift from
fire-sensitive conifers such as hoop pines and bunya pines to fire-resistant
trees including eucalypts. A decade later, palaeoecologist Peter Kershaw of
Monash University in Melbourne and colleagues at the University of Tasmania
found similar evidence in a core from the seabed off the Great Barrier Reef.
Recently, Kershaw and Patrick Moss refined that work to show a sharp increase
in the amount of charcoal in sediment and a pronounced change in vegetation 130
000 years ago. Kershaw says that palynologist Sander van der Kaars, now at
Monash, has unpublished evidence from a core taken off Lombok, Indonesia, of a
change from forest to grassland vegetation about 190 000 years ago, and a
telltale charcoal peak 200 000 years ago. Kershaw argues that human activity is
the only reasonable explanation for these changes.
Easy crossing
Mike Morwood, an archaeologist with the University of New England at Armidale
in New South Wales, is not surprised by these results. After all, skulls of
early humans, known as Homo erectus, found on Java have been dated to 1.8
million years ago (“Human origins: the challenge of Java’s skulls”, New
Scientist, 7 May 1994, p 36). And Morwood and Dutch colleagues have unpublished
dates for tools found on the east Indonesian island of Flores, which suggest
that H. erectus was busy there more than 700 000 years ago.
If such ancient people could reach Java and Flores, it seems reasonable that
hundreds of thousands of years later people could have found their way to
Australia. Fullagar and his colleagues point out that before 135 000 years ago,
the sea level fell dramatically, which could have made the sea voyage from
mainland Asia to Australia easier.
The date of arrival of the first Australians is important not just in itself,
but also for its impact on theories of human evolution. Until three years ago,
H. erectus was thought to have developed in Africa about 2 million years ago and
then spread across the globe. Dating of the Javan skulls at 1.8 million years
ago has placed a large question mark over that theory.
The origins of modern humans are equally contentious. Supporters of the “out
of Africa” theory argue that modern humans walked out of Africa about 100 000
years ago, and outcompeted their more ancient rivals wherever they went. In
contrast, promoters of the “multiregional” hypothesis believe that H. erectus
populations throughout Africa, Europe and Asia evolved simultaneously into
modern humans.
The date at which humans arrived in Australia, and whether they were ancient
or modern, has big implications for these two competing theories, says Alan
Thorne, a palaeoanthropologist at the ANU and an advocate of the multiregional
hypothesis. “Any date beyond 120 000 years makes it difficult for the out of
Africa theorists,” he says. “Their dates would suggest that if modern humans
evolved in Africa they must have invented the bicycle at the same time so they
could cycle around to catch the first rafts to Australia.”
Conversely, if the first Australians were H. erectus, “they must have been
more technologically sophisticated than we thought”, says Chris Stringer,
principal researcher of the human origins group at the Natural History Museum in
London. An alternative notion is that modern humans left Africa before 100 000
years ago. Backing for this idea comes from physical anthropologist Colin Groves
of the ANU. He points out that “transitional” fossils—part-way between
ancient and modern humans—found at Florisbad, South Africa, have been
redated to 250 000 years ago. That work, by Rainer GrĂĽn also of the ANU,
suggests that modern humans developed earlier than first thought. “So we have
much more time to get people to Australia or wherever we want to get them,” says
Groves.
Groves, Stringer and just about every other toiler in the field would really
like to find human skeletal remains or teeth, which have been conspicuously
absent from early Australian sites. The next best thing would be to firm up the
Jinmium dates. Until then, all the implications of Fullagar and his team’s
research will be in doubt. As Stringer says: “I’m holding back to wait for these
dates to be confirmed by another lab.”
* * *
Dates from the forbidden zone
MINERALS such as quartz and feldspar are semiconductors, and their electrons
exist in energy bands called the valence and conduction bands. Between these two
is the band gap, a “forbidden zone” where electrons normally cannot exist. But
naturally occurring crystals have structural defects, and electrons that are
excited out of the valence band into the forbidden zone can lodge in them.
These electrons can stay in place for millions of years, until their refuges
are exposed to high temperature or light. At that point, all the electrons empty
from their traps and recombine with atoms in the crystal lattice, emitting their
stored energy as light. The intensity of this luminescence gives a measure of
how long since a sediment last saw the light, or since a piece of pottery was
last exposed to high temperature.
In sediment, for example, quartz and feldspar act like a stopwatch. Sunlight
sets the clock to zero. But once the crystals are buried by more sediment, they
begin to accumulate electrons in the forbidden zone—the necessary energy
coming from radiation released by surrounding rocks and soil.
So scientists wanting to date a sediment must first measure the radiation
level from the surroundings and work out the annual dose to a crystal. They also
expose some of the crystals to known doses of radiation to see how a given dose
changes the intensity of luminescence. They then heat up the sediment samples
and measure the thermoluminescence (TL) given off, or expose the samples to
light and measure the optically-stimulated luminescence (OSL). By
calculating backwards from light intensity to total radiation dose and dividing
it by annual radiation dose, researchers gauge the age of a sediment.
David Price of the University of Wollongong in New South Wales used TL to
date the Jinmium deposits. On relatively young sediments, he found that the
technique correlated well with ages produced by a second method, radiocarbon
dating. But it is the older sediments that have generated controversy. Bert
Roberts of La Trobe University in Melbourne is concerned that these sediments
may be contaminated with pieces of rubble from very old bedrock nearby. The
“clocks” in the bedrock could have been set to zero long before the sediments
into which they fell. And since TL is performed on about 1000 grains of sediment
at a time, these contaminants could skew the analysis, giving a much older age
for the entire sample.
“The only way to resolve the problem is to do dating of single grains,” says
Roberts. Only OSL is suitable for single-grain work. Along with Ann Wintle of
the University of Wales and Andrew Murray at Ris National Laboratory in
Denmark, Roberts has just finalised procedures to analyse single grains from
Jinmium with OSL. He claims this will settle the dispute once and for all, as
grains of different ages will be “cleanly separated from one another”. That
analysis will begin early next year and take several months to complete, so the
Jinmium thriller will remain a nail-biter for a good while yet.