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If you have walked on a dune surface after windy conditions have settled, you may have been privileged to recognize one of Nature's wonders: scratch circles. These are structures formed when the end of a tethered object is passively rotated into the surrounding sediment. In other words, a flimsy frond or blade of grass that is attached to the ground will blow in the wind, and its loose end will inscribe a perfect circle or perfect arc, with the point at which it is attached becoming the center of the circle or arc.

The was in 1886. In 2018 a of their occurrences in the global geological record was published.

In our team's of trace fossils on the Cape coast of South Africa we realized that the and surfaces we were researching, dating back as much as 3 million years, provided substantial evidence of scratch circles and scratch arcs. This evidence included several phenomena that have not previously been observed.

After further investigation we've . We're particularly excited about two key takeaways.

Firstly, the time span in which scratch circles or scratch arcs have previously been identified ranges from about 600 million to 60 million years ago. The scratch circles we have found may be as little as 100,000 years old, making them the most recent examples yet identified in the geological record and substantially extending their age range.

In one case we could even identify the probable type of plant (a kind of sedge) that was responsible for creating the circular feature. We also documented the first cases of scratch arcs occurring in vertical cliff faces, perpendicular to bedding plane surfaces, as shown in by Andre van Tonder.

Secondly, there appear to be two possible explanations for circular patterns with central depressions in Pleistocene deposits on the Cape coast. One is the typical scratch circle or scratch arc as described above, made by a plant. The second is an ammoglyph, a pattern made by ancestral hominins in sand, that is now evident and interpretable in .

We speculate that the first type may have been the inspiration for the second, and that ancestral humans may have seen these perfect circular forms and found innovative ways to mimic them. If we are correct, then this would be among the oldest known evidence of palaeoart (really ancient, early forms of art).

Circles in the sand

We already know that the Cape south coast is one of the places in which some of the earliest known palaeoart was created, at sites like , and through the ammoglyphs we have .

The oldest purported ammoglyph that we have dated through a technique called is . It seems likely that sand formed the original canvas for the earliest artists, as drawing on it would have been much quicker and easier than engraving or drawing on rock walls, trees, bones, or shells.

There is a precedent for astute ancestral humans being acutely aware of their environment and mimicking what they encountered. It has that ochre (a pigmented type of earth) used in body decoration may have originated after people observed the bearded vulture (lammergeier) bathing in ochre and covering its feathers with . This would be an example of bio-mimicry—humans copying what they saw in the world around them.

Scratch circles in sand, with clear evidence of how they were formed, would have been present on those Pleistocene dune surfaces on what is today the Cape south coast. We hypothesize that ancestral humans noted these perfect circular forms, inferred their origin, and realized they could try to replicate them in sand. This can be done by anchoring one end of a forked stick in the sand and then twirling it, thus inscribing a circle with the other end. It's a behavior we've written about in previous research about ammoglyphs. This natural curiosity about and replication of circles has .

A human origin

Using sticks in the way we're describing is not the only method for drawing circles in sand. One can also kneel down, place one's elbow in the sand, and rotate one's forearm with one's finger inscribing an arc. This may not, however, result in a perfect arc—flexing or extending one's wrist would affect the symmetry.

We have found a pattern on the De Hoop Nature Reserve coastline (which we call the De Hoop ammoglyph) that suggests this mechanism of creation, subsequently bolstered by our team's experiments in sand. In fact, the arc being imperfect is one of the features that supports a human origin—scratch circles made by plants are much more perfect, as is the forked stick technique. We can estimate the length of the forearm of the artist of the De Hoop ammoglyph; it appears to be consistent with that of a child or adolescent (or very small adult) artist.

It is extremely fortunate that an area in which humans began thinking and behaving as we do (and creating art in sand) happens to be exactly where the beaches and dunes they inhabited have become cemented and preserve this record of palaeoart in stone. This provides us with a window into the activities of our ancestors that we might not be able to discern in any other way.

Scratch circles, it seems, are not just spectacular in their own right, but might have also set in motion a chain of events that led, for example to the splendors of in France 34,000 years ago and other subsequent masterpieces. The findings suggest that our capacity as a species for astute observation, followed by mimicking, perhaps allowed us to leap forward and develop the beginnings of what we now know as art.

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