The extraordinary cache lies in a remote and sparsely populated region of north-central Australia. Known by the Aboriginal name of Djulirri (rhymes with "Hillary"), the site was until now almost completely unknown to science.
The rock walls of Djulirri bear images of kangaroos, the now-extinct Tasmanian tiger, sailing ships from the 1800s, humans performing a ritual with a snake, European missionaries, even a biplane. In some places there are 20 layers of artworks, one painted atop the other.
The oldest paintings at the site are 12,000 to 15,000 years old; the newest, roughly 50.
"I've been documenting and visiting rock art sites for about 30 years now," says Paul Tacon of Griffith University in Australia, one of the scientists leading the detailed study of the site. "And Djulirri is one of the most impressive and outstanding sites I've ever been to."
"This is art that is significant internationally, not only for its beauty but for the insights it gives into how humans adapt to change," Claire Smith, president of the World Archaeological Congress, says via e-mail.
The first scientific report based on in-depth study of the site is in the June issue of the journal Antiquity. Written by Tacon and others, the paper describes an image unique to Djulirri: a stencil of a bird, probably a species called the singing honeyeater. Scientists say the image may be more than 9,000 years old. The artist created it by holding a real bird against the rock wall and skillfully blowing red paint over it to create an outline.
In another paper to be published in June, the Djulirri scientific team will report that a depiction of a Southeast Asian boat was painted no later than the 1600s. That date overturns the widespread assumption that Aboriginal people lived in isolation until the arrival of British explorers in the 1700s.
One scientist visited the site in the 1970s, but after that it was lost to research. The first thorough study of Djulirri began in 2008.
Aboriginal artists probably relied on the rock images to pass on knowledge and to document their history, including contacts with visitors from different lands, Tacon says, adding that native Australians "refer to these sorts of sites as their libraries or their history books."
Unlike many of the most famous prehistoric rock paintings, this art was not made in caves. Instead it was created in a series of above-ground rock "shelters," roomlike spaces with rock walls and, in some cases, rock ceilings. The site would have made an ideal place for families to camp during their search for food because of its spaciousness and its natural spring, Tacon says.
Perhaps that's why artists chose Djulirri's rocks for their canvas again and again. No other site in Australia has so many paintings in so many different styles, Tacon says.
However, it's not unusual in other parts of the world to find rock art sites that have been used continuously for millennia, says rock art expert David Whitley of ASM Affiliates, a U.S.-based archaeological consulting group.
Djulirri is interesting and significant, he says, but North America alone boasts many examples of rock art sites that seem to have been used for 10,000 years. That's close to the age span for Djulirri.
Those who've seen Djulirri say it's also distinguished by the sheer quantity of art relating to the Aborigines' contacts with outsiders. That makes the spot a valuable window into the experience of people having their first encounters with foreign cultures, says Ines Domingo Sanz of the University of Barcelona.
"We usually reconstruct the contact period through the views and travel diaries of the Europeans," Sanz writes in an e-mail. "For me, these paintings are like the visual travel diaries of the indigenous people, who used the walls of this site complex to reflect their own views on this story."