Around 5,500 years ago, a man living in a coastal settlement in northern Chile died and was buried in a round stone structure built atop a pile of discarded seashells.
He was not buried alone. The grave contained four people: two males, one woman and a baby. The four were laid to rest on the shore of the Atacama Desert, one of the most arid and harsh environs on the planet.
But he had drowned. It could even be inferred that the man had drowned in the sea not far from shore, Prof. Pedro Andrade of the University of Concepción in Chile, James Goff of Britain’s University of Southampton and colleagues report in the Journal of Archaeological Science.
Absent records, and there were none at the time, determining this man’s cause of death in Neolithic Chile could only be elucidated by forensic archaeology. Drowning is hard to determine as a cause of death in an ancient body, long bereft of flesh. It leaves no marks on the bones.
But the team could apply a technique used in modern cases where drowning is suspected: the "diatom test."
Diatoms are a vast group of spectacularly beautiful single-celled algae that have siliceous exoskeletons and if they’re found in a person’s bone marrow, then the person inhaled water.
Bone marrow? Not lungs? Well yes, lungs too, but this is the thing. When one drowns, the pulmonary alveoli in one’s lungs rupture. “Saltwater enters the bloodstream and can be transported throughout the entire body by the capillary network and into the ‘closed system’ of the bone marrow,” the team explains.
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Having silicon-based external skeletons, these microscopic plants survive this traumatic journey from peacefully floating in water to being breathed in and violently knocked about the system only to end inside a bone. They survive structurally at least, and in this case were identified around 5,500 years later in the person’s large bone marrow, after the drowning event.
Since the diatoms that live in freshwater and the sea are different species, identification of the inhaled species suffices to signal the environment of the fatal event.
Diatom testing had been used in another archaeological forensic investigation: of a child who fell down a well in Neolithic Sweden, the team says. In that case, just four diatoms, of the freshwater type, were found. But that sufficed, the team notes.
He died young
The prehistoric Chilean man had, as said, been found in a multiple burial with another man, a woman and a baby. His head was separated from his body, but present; his teeth indicate that he died age 35 to 45, the team writes. He had been 160 centimeters tall – about 5 feet, 2 inches, and he was not a healthy camper. Despite his relative youth, he had arthritis severe enough to scar his bones and, based on the condition of his eye sockets, is thought to have been severely iron-deficient – due to eating animals or fish infected with tapeworm. His teeth were terrible, too.
The skeleton of the baby was laid between his legs, the bones of which indicate that the man spent a lot of time squatting – possibly to collect shellfish. The condition of his arm bones suggest he had also done a lot of rowing and harpooning.
Radiocarbon dating indicated all four of the people buried in the round structure on the midden had died at about the same time, which is also indicated by their shared interment. One possible theory is that they were all killed by a tsunami, which is a reasonable enough theory for the region.
Chile is one of the more seismically active places on Earth. In May 1960, it suffered the most powerful earthquake in recorded history: 9.5 on the Richter scale (estimates range from 9.4 to 9.6). Striking southern Chile, the “Valdivia earthquake” lasted 10 minutes, according to historical records, and triggered massive tsunamis that devastated, among other areas, the islands of Hawaii.
The point is, among the risks the coastal hunter-gatherers of Neolithic Chile faced were earthquakes and tsunamis. Hence, the discovery of a prehistoric multiple burial suggested that as a possible cause.
Flooding from a vicious paleo-storm off the Atacama would also have been a plausible cause of drowning. Terrible storms are another feature of the Chilean coastline thanks to the El Niño-Southern Oscillation, aka ENSO, generator of both the El Niño and El Niña weather phenomena.
And indeed, this person may have died from tsunami or terrible storm, but people being buried together doesn’t necessarily mean they all died from the same cause, the team stresses – and in this case, apparently they didn’t.
This man died of drowning in the sea based on the diatom test, but two other persons they checked showed no evidence of drowning. Among other things, that indicates the diatoms in the bone marrow of the first body weren’t a side-effect of contamination, which had been a concern for the researchers.
Living by the Atacama is not easy, with no water source aside from small springs along the coast. Yet hunter-gatherers eked out a living along the coast for the last 12,000 years, if not consecutively – the evidence indicates that sometimes they left.
Over the millennia they ate chiefly fish, mollusks, birds and whatever mammals they could catch. The coastal population began to increase about 7,500 years ago, as they got cleverer in harvesting the bounty of the sea. The team notes shell fishhooks, harpoons, bone fishhook weights, knives and scrapers – as well as shell beads, which may speak of trade. The archaeologists even identified a special type of hook used to hunt octopi.
As of 5,500 years ago, social complexity may have increased, the archaeologists surmise, based on stone structures built atop their garbage piles of mollusk shells (middens) – which are thought to have perhaps served for funerary purposes.
One theory had been that the man who died wound up with diatoms in his bones from gorging on seafood, leading the microscopic algae to be absorbed in the gastrointestinal system and bandied about the body. The team notes that there is zero evidence for any such possibility, however.
Given all the above, the team surmises that the man with diatoms in his bones probably drowned by accident, likely in shallow water but possibly in open water.
Over a thousand years after his body was laid to rest with those of other people, something happened. Signs of stable communities along the Atacama coast disappear and are replaced with signals of intermittent occupation, the team writes. Changes in diet also support their theory that there were “extreme climatic and tectonic events” – storms and quakes. Separate research has identified a paleo-tsunami about 4,000 years ago. It still remains possible that the unfortunate man did die in such an event even if his grave-mates did not.