The world’s oldest drawing might be easy for a casual observer to miss: a 38.6mm (1.52 inch) long flake of silcrete (a fine-grained cement of sand and gravel) with a few faint reddish lines drawn on one smooth, curved face using an iron-rich pigment called ocher. The lines would have been bolder and brighter when the drawing was new, according to University of Bergen archaeologist Christopher Henshilwood and his colleagues, but over time they’ve lost pigment to rinsing and wear, leaving them faint and patchy. But an archaeologist working at Blombos Cave, about 300km (186 miles) east of Cape Town, South Africa, noticed the markings while analyzing stone flakes and debris excavated from a 73,000-year-old layer of the site.

The design features six nearly parallel lines, with three curved lines cutting across them at an oblique angle, but it hints at a more complex piece of work. All the lines cut off abruptly at the edges of the flake, which suggests that the pattern archaeologists see today is just a fragment of something originally drawn on a larger surface and later broken.

“The pattern was probably more complex and structured in its entirety than in this truncated form,” wrote Henshilwood and his colleague. Modern viewers will likely never know what the rest of the drawing looked like—or what it meant to people 73,000 years ago.

You’re never too old for crayons

Even if we can’t grasp the prehistoric artist’s meaning, we can still understand a surprising amount of detail about their technique. In part, archaeologists approached those questions the same way art students for centuries have tried to learn the techniques of the great masters: namely, by copying their work. Henshilwood and his colleagues marked up numerous pieces of smooth silcrete with ocher crayons and ocher-based paint, trying to replicate the look of the anonymous Stone Age artist’s cross-hatching. The best match came from a soft ocher crayon with a pointed tip about 1.3 to 3.3mm across.

On close inspection, the lines have a sort of patchy appearance, which comes from loose ochre powder falling into the low points and eventually washing or wearing away, while ochre stuck better to the higher, smoother bits of the rock; think about how a modern crayon leaves a patchy, uneven line if it’s drawing on a rough surface. Paint, on the other hand, left a much smoother line that didn’t match the ancient drawing.

Henshilwood and his colleagues also noticed that most of the lines seem to have been drawn in a single stroke, but one of them (line 5 on the diagram) is thicker than the others and shows evidence of strokes going in both directions, so the artist may have scribbled back and forth a few times to thicken the line. Modern viewers can only wonder why.

Meanwhile, the “canvas” the prehistoric artist chose is as interesting as the technique. This particular flake of silcrete appears to have once been part of a grindstone used to grind ocher into powder, based on the unusual smoothness of its curved face and the microscopic traces of ocher residue still clinging to its surface. And it seems that someone originally shaped that surface as a striking platform (a prepared, flat surface from which to strike smaller stone flakes). Later, grinding made it much smoother than similar surfaces on other silcrete flakes—a perfect place to draw with an ocher crayon.

We’ve been artists for a long time

It’s no real surprise that humans were drawing abstract designs 73,000 years ago. Ample evidence from Africa, Asia, and Europe shows that humans—and our hominin relatives—learned how to use symbols and make art early on. Archaeologists have found zigzag engravings on shells from Java, which were probably the work of Homo erectus 540,000 years ago. And Homo erectus probably also engraved more-or-less parallel lines on bones found at a 370,000-year-old German site.

At Blombos Cave itself, archaeologists have unearthed shell beads, along with engraved bones and pieces of ocher dating from 100,000 years ago to 72,000 years ago. They’ve also found a 100,000-year-old kit for creating pigmented liquid: ocher, heated seal bone, charcoal, and other processing materials. But this small silcrete flake is the oldest drawing (as opposed to engraving) ever found. It contains the same type of cross-hatched pattern as engraved artifacts from the site, so the crayon marks on the rock “demonstrates their ability to apply similar graphic designs on various media using different techniques,” wrote Henshilwood and his colleagues.

Most of the previous examples of prehistoric drawing date to at least 42,000 years ago, although recently dated Neanderthal cave paintings in Spain are probably around 65,000 years old.

Nature , 2018. DOI: 10.1038/s41586-018-0514-3 (About DOIs).