Using a microscope, a laser and a scanning electron microscope, they determined that the marks were on top of the rock and that they were made from red ocher, a type of natural pigment that was often used to make prehistoric cave paintings. In fact, ancient humans in the Blombos Cave were making ocher paint as far back as 100,000 years ago.

“Then we had to determine how did they make those lines?” Dr. van Niekerk said. “Were they painted or drawn on?”

They recreated ocher paint, then fashioned a wooden stick into a brush and made strokes on stone flakes comparable to the specimen. They also made an ocher crayon and drew lines. They then compared the paint markings and crayon markings with what they had seen on the artifact.

They determined that the ancient crisscross pattern was a drawing, not a painting, made with an ocher crayon tip that most likely measured only about 1 to 3 millimeters in thickness.

That distinction between a painting and drawing is important, according to Dr. Henshilwood, because ocher paint batches can dry. That makes it less useful than an ocher crayon used by an ancient human whenever she or he wanted to make symbols without going to the trouble of mixing up paint.

Dr. Henshilwood and his team also showed that the red lines were drawn onto a smooth surface. That indicated that the flake was once a part of a larger stone that the prehistoric humans may have used to grind ocher. They also showed that the original red lines most likely stretched past what was seen on the stone flake before the grindstone was broken.

They cannot say with certainty what the purpose of the drawing was and whether it was mere doodling or if it held some greater meaning. But they have their conjectures.