Archeologists have discovered the earliest known drawing created by humans, scrawled on a rock at the shoreline of South Africa. Dating back some 73,000 years, the mysterious picture consists of three lines intersected by six angled lines, like a more complicated version of the hashtag (#).

The picture was unearthed at Blombos Cave, a site about 300 kilometers east of Cape Town. The cave was frequented by humans as early as 100,000 years ago and is packed with evidence of tool-making and symbolic designs. The find is described in new research published in Nature, led by archeologist Christopher Henshilwood at the University of Bergen, who has been leading excavations at Blombos Cave since 1991.

Image: D'Errico/Henshilwood/Nature

“This notable discovery predates the earliest previously known abstract and figurative drawings by at least 30,000 years,” Henshilwood and his co-authors note in the paper. “This drawing demonstrates the ability of early Homo sapiens in southern Africa to produce graphic designs on various media using different techniques.”

Among the previous record-holders for oldest human-made drawings are hand-stencils found in a cave on the Indonesian island Sulawesi, which date back over 40,000 years. Neanderthal artists may have also produced drawings in caves on the Iberian peninsula some 64,000 years ago.

Image: Cayho Ramadhani

To determine that this drawing was intentionally produced by humans, the team examined the pattern with both optical and electron microscopes, and RAMAN spectroscopy, which is an imaging technique for resolving precise molecular structures in samples. Those tests revealed that the lines were drawn with an artificial red ochre pigment, perhaps fashioned by the cave inhabitants from clay, sand, and iron oxide.

The researchers also reconstructed tools that could have been used to apply the pigment, and concluded that the stripes were made by a primitive crayon with a tip that measured about one to three millimeters in diameter.

While it’s encouraging that the team were able to discern so many details about the drawing, the most tantalizing mystery—what the image is supposed to represent—remains unsolved. The team is not sure if it is even a complete symbol, or if it is a fragment of a larger picture.

Blombos Cave interior. Image: Magnus M. Haaland

Francesco d'Errico, the study’s second author, says the team is pursuing multiple leads to narrow down what motivated early humans at Blombos Cave to draw this pattern.

“We work with neuroscientists and have created with them experimental protocols to investigate what area of the brain are activated during the perception of the earliest engravings,” d'Errico told me in an email. “We are also analysing unpublished evidence from South Africa and exploring how and when similar behavior emerged in East.”

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Regardless of what prompted the artist, or artists, to draw lines on a rock 73,000 years ago, the image is more proof that the human instinct to externalize abstract thoughts runs deep into our prehistory.