A gallery’s worth of rock art decorating the inside of a cave in Argentina is several millennia older than once thought and contains hundreds of drawings that span 100 generations.

At one time, archaeologists dated the art — located in Patagonia, a region in South America’s southern tip — as being only several thousand years old. But a new analysis has revealed that some of the works actually date to as early as 8,200 years ago and were created during the late Holocene epoch (11,700 years ago to present), according to a study published Wednesday (Feb. 14) in the journal Science Advances.

“It turned out to be several millennia older than we expected,” study lead author Guadalupe Romero Villanueva, an archaeologist with the Argentine National Research Council (CONICET) and the National Institute of Anthropology and Latin American Thought (INAPL), told Live Science. “We got surprised.”