Jim McMahon/Mapman®

While out for a walk on a beach in western Australia, a woman made an unbelievable discovery. She stumbled across the oldest known message in a bottle—but it wasn’t an SOS or a treasure map.

The bottle, which had been tossed into the Indian Ocean more than 130 years ago, was part of a science experiment conducted by the German Naval Observatory to learn more about ocean currents. According to the scroll of paper inside the bottle, scientists threw it overboard from a ship called Paula on June 12, 1886, as the vessel made its way from Cardiff, Wales, to Makassar, Indonesia.

As part of a decades-long experiment—which ran from the 1860s to the 1930s—thousands of bottles were thrown from German ships as they sailed around the world. Each message asked that the finder send the note to the observatory in Hamburg, Germany. Only 662 were ever returned. 

The bottle represents some of scientists’ earliest work in trying to better understand the world’s oceans, says Ross Anderson, a museum curator in Australia.

“It’s a once-in-a-lifetime, once-in-a-century . . . find,” he told reporters.