Some 5,000 years ago on the coast of Chile’s Atacama Desert, a fisherman drowned in the cold waters of the Pacific. It’s the life-and-death story of an individual who lived millennia ago, and one that researchers are now able to tell, thanks to a twist on a modern forensic technique.

The “diatom test,” used today to identify victims of drowning, relies on what happens to the human body during the event: Inhaled water ruptures the lungs and is pumped around the dying body, including along tiny capillaries that go through bones and into the marrow.

Forensic scientists examine the marrow of the dead to look for diatoms—microscopic algae with shells of silica—that are characteristically found in drowning victims. Now, researchers