Skulls cremated at Stonehenge thousands of years ago have yielded stable isotopes, forensically answering some questions about the ancient peoples using the megalithic monument as a massive graveyard.

Despite total immolation some 5,000 years ago, the chemical traces were locked into the calcified bone structure itself—allowing 21st century scientists to place their point of origin in life, according to the new study in Scientific Reports.

“The recent discovery that some biological information survives the high temperatures reached during cremation (up to 1000 degrees Celsius) offered us the exciting possibility to finally study the origin of those buried at Stonehenge,” said Christophe Snoeck, lead author, who performed the work during his doctoral research at the University of Oxford’s School of Archaeology.

“The really remarkable thing about our study is the ability of new developments in archaeological science to extract so much new information—from such small and unpromising fragments of burnt bone,” added Rick Schulting, another of the Oxford authors.

The 31 pieces of bone came from 25 individuals, and had originally been unearthed in the 1920s from a network of 56 pits around the inner circumference of Stonehenge, known as Aubrey Holes. The bones had been reinterred, and were easily located about a century after their first discovery.

Radiocarbon dating placed them in two time frames: between 3180 B.C. and 2965 B.C., and 2565 B.C. and 2380 B.C., according to the paper.

The thick fragments of occipital bone were first assessed by infrared spectroscopy, to determine they were fully calcined.

Then they were cleaned, crushed with a mortar and pestle, and then analyzed by FTIR-ATR (through Agilent and Pike Technologies tools).

The proportion of Strontium-86 and Strontium-87 was calculated using a Multi-Collector Inductively-Coupled-Plasma Mass-Spectrometry procedure. Ultimately, the isotope ratios were measured on a Nu Plasma MC-ICP mass spectrometer at Universite Libre de Bruxelles. The statistical analyses were carried out comparing the chemical signatures, as compared with places around Britain.

They found 10 of the 25 deceased were not local. They had hailed from far western Britain, like modern-day Wales—and the same place where some of the bluestone at Stonehenge had been sourced. The region is far different than the chalky environment of Wessex around the megaliths, they conclude.

For those 10, they had spent the last decade of their lives living over the hills and far away.

“Those with the highest values point to a region with considerably older and more radiogenic lithologies, which would include parts of southwest England (Devon) and Wales (parsimony making locations further afield—including parts of Scotland, Ireland, and continental—less probable),” they write. “Since measurements on bone reflect a mixture of the foods consumed over the decade or so prior to death, there is also a temporal aspect to be considered … those moving later in life from west Wales to the vicinity of Stonehenge would present a signal increasingly attenuated by the consumption of local foods, while migrants arriving on the Wessex chalk more than a decade before death would effectively become ‘local’ in terms of their bone strontium isotope ratio.”

The conclusion opens up new interpretations of what the monument must have meant in its earliest phases, some 5000 years ago, they add. And it began with the discovery of the chemical isotope traces.

“This new development has come about as the serendipitous result of (Snoeck’s) interest in the effects of intense heat on bones, and our realization that that heating effectively ‘sealed in’ some isotopic signatures,” added Julia Lee-Thorp, head of Oxford’s School of Archaeology.

Previous studies have indicated that some isotope signatures can survive intense heat. For instance, expert Wolfram Meier-Augenstein of Robert Gordon University in Scotland, tackled some of the microscopic nuances of contemporary fire scenes in his milestone text, the second edition of Stable Isotope Forensics. Meier-Augenstein recounts how the very matchsticks used to ignite arson blazes can still be matched to source locations, based on the wood used from geographic locations.