How do people date in Saudi Arabia

Mysterious rock art can be dated using a new method

Images immortalized in rocks are among the oldest artistic representations of mankind. Such petroglyphs may reveal a lot about the world of their creators, but when they were scratched into the rock is of course difficult to date. For decades, scientists in the Hima region in southwest Saudi Arabia have been working on the corresponding rock art. Little is known about their origin, however.

To this day, archaeologists do not agree on how old these images are. Now, however, an international team headed by Meinrat O. Andreae from the Max Planck Institute for Chemistry has developed a method and presented it in the journal "The Holocene" with which the rock art can be dated more precisely.

Desert varnish as a dating aid

The researchers examined the so-called "desert varnish" in and around the images. Desert varnish is a dark coating that occurs on stones and rock walls. The wafer-thin, manganese-rich crust occurs on almost all types of rock. This dark surface offered the creators of the petroglyphs an ideal background: the freshly cut images stood out clearly against the black layer. From a geochemical point of view, petroglyphs are important because they can be used to study the formation of desert varnish over a period of several thousand years.

With the help of a handheld spectrometer based on X-ray fluorescence analysis, the scientists measured the chemical composition of the image surface and the surrounding rock directly on site. In addition, samples were examined in the laboratory using femtosecond laser ablation ICP mass spectrometry. The data were then compared with measurements on rock art, which could be dated more precisely based on the font used or engraved dates.

Up to 7,000 years old

With the help of the measured manganese and iron values, the MPIC researchers were able to precisely date the petroglyphs of previously unknown age in the Hima region. "We noticed that the pictures were taken almost throughout the entire Holocene," says Andreae. The oldest among them are around 7,000 years old, the youngest were created a few hundred years ago.

"Our dates correspond to the culturally or ecologically derived age of the animal and human figures depicted in the rock painting, as well as to the font styles used in different periods of time," explains Andreae. In a next step, the scientists want to use the new method to evaluate data that has already been collected from another region of Saudi Arabia. As a result, expeditions are planned in North America and China. (red, May 27, 2019)