A long time ago, two kids in Quesang, on the Tibetan Plateau, had a bit of fun. They left a set of handprints and footprints on a travertine boulder between 169,000 and 226,000 years ago. Researchers now believe that these fossilized impressions, apparently left intentionally, could be the world’s oldest known cave art.

A team of researchers led by Professor David Zhang from Guangzhou University found the hand and footprints in travertine formed around a hot spring. Travertine is freshwater limestone that when is first deposited it forms a sludgy mud that you can push your hands and feed into. When it’s cut off from water, the travertine hardens into stone, keeping the impression like a form of slow-acting cement.

“How footprints are made during normal activity such as walking, running, jumping is well understood, including things like slippage,” Thomas Urban, co-author of the new paper, told Gizmodo. “These prints, however, are more carefully made and have a specific arrangement—think more along the lines like how a child presses their handprint into fresh cement.”

Researchers used uranium, a naturally found radioactive element, to date the prints. They estimated that the impressions were left in the Pleistocene epoch – which occurred 2.6 million to 11,700 years ago. The marks were likely left by two children, one the size of a modern-day 12-year-old and the other the size of a 7-year-old. 

Still, the team couldn’t tell what species of archaic humans actually left the prints. Study co-author Matthew Bennett told Live Science that “Denisovans are a real possibility,” but also mentioned that Homo erectus was also known to inhabit the region. He said “there are lots of contenders” but that they don’t know at this point. 

Is this really art?

As the researchers explain in an article, hand shapes can be commonly found in prehistoric caves. The hand is usually used as a stencil, spreading pigment around the edge. The oldest known examples are the caves in El Castillo, Spain, and Sulawesi, Indonesia. Now, whether this is art or not, that’s a big debate.

Defining what is art depends on how you look at things. The ancient philosopher Aristotle, for instance, thought the Greek concept of mimesis (to mimic) provided us with a definition for what makes art. In this view, art is a copy of something else. The artist sees something and imitates it. Much of what is art fits this definition up until the early XX century when the idea of art became more debated. 

The hand and footprints meet the criterion of mimic art, the researchers argued. The artist, in this case, the two kids in the Tibetan Plateau, took a form already known through lived experience (having seen their own hands and feet) and took that form and reproduced it in a context and pattern in which it wouldn’t normally appear. 

“Whether such a behavior is artistic depends on the definition one applies—but it gets into a class of behaviors that is generally more complex that is seen with other animals,” Urban told Gizmodo. “Symbolic behaviors such as language, religion, and art must have simpler manifestations early in the human story.”

The study was published in the journal Science Bulletin.