About 9000 years ago, a group of people living in South America, near what is now the border between Chile and Peru, lived mainly by fishing. Many of them — including an unusually high number of babies and fetuses — died mysteriously.We know about these people, called the Chinchorro, because they uniquely mummified every member of their society — young or old, of high status or low. Archaeologists are unsure why the Chinchorro performed these rites ubiquitously, but the level of interest in the mummified remains is high. Unfortunately, the method used to create the mummies removed most of the organic matter, leaving little but teeth, hair and bones to study.Analytical chemist Dula Amarasiriwardena and a team of students from Hampshire College in Amherst, Mass., started with the hair.Last summer, Amarasiriwardena visited an ancient village near the Atacama Desert, a highly arid land through which a river carried drinking water from the Andes to the Chinchorro, and collected hair samples from several mummies. During a previous visit, in 2003, hair was collected from living residents because some of the minerals that people ingest relocate in minute amounts to the hair, leaving behind a record. After bringing the samples back to the lab, the team used a laser to ablate material from each strand, then searched the ablated sample for trace minerals using an inductively coupled mass spectrometry system.Perhaps surprisingly, the mass spectra indicated dangerously high levels of arsenic — in hair samples from both the mummies and the residents. The investigators cannot know with certainty whether the arsenic killed Chinchorro tribe members prematurely, but they do know that the level is about 11 times higher than normally found in human hair and is far from healthy.Amarasiriwardena’s group is continuing its investigation of the mummies by using similar techniques to probe the teeth. According to team member Cameron Peebles, teeth can help reveal the larger picture, including nutrition and migratory patterns.So, be careful what you eat and what you drink — unless you don’t care that a future archeologist might analyze you.