Radiocarbon dating of bones from skeletons discovered at Machu Picchu in 1911 shows that the Inca citadel had been occupied by 1420 years earlier than anticipated. (Image credit: Courtesy Yale University)According to radiocarbon dating of human remains at the archaeological site, the Inca citadel on Machu Picchu in Peru's mountaintop was constructed and occupied decades before previously thought.It is possible to determine how early the Inca Empire came to power by learning that Machu Picchu was discovered to have been inhabited as early as 1420, if not earlier."Machu Picchu ranks among the most renowned archaeological sites in the world," said Richard Burger, Yale University's archaeologist, and anthropologist.Related: Image gallery for Inca Child MummiesThese historical accounts suggest that Machu Picchu was constructed between 1440-1450.Burger and his coauthors discovered that Machu Picchu was inhabited 20 years earlier than originally thought.Archaeologists believe Machu Picchu was built by the emperor Pachacuti in 1420. Pachacuti is the one who is credited for greatly expanding the Inca state through the conquest of neighboring areas. (Image credit: traumlichtfabrik via Getty Images)'Lost city'Machu Picchu can be found high up in the Andes at almost 8,000 feet (2.430 meters) above sea level on a mountain ridge of Peru's Eastern Cordillera mountain group.After the Spanish invasion in 1530s, it was abandoned. However, locals knew its exact location. Hiram Bingham, a Yale University professor, led two expeditions to the site between 1911 and 1912. It became an iconic symbol of Inca civilization over the years that followed.Archaeologists believe Machu Picchu was built to house the emperor Pachacuti. He was a hereditary ruler who was born in Cuzco (the Inca capital) in what is now southeastern Peru. A chronology that is based on Spanish documents after the conquest shows that the citadel was constructed around 1438. This was after Pachacuti rose to power and expanded the empire to the surrounding regions. .Burger and his team examined 26 remains from servants believed to have been found in Machu Picchu's three cemeteries.The new analysis used an sensitive technique called accelerator mass spectrometry to measure the ratio of certain versions or isotopes of carbon in bones. The radioactive isotope of carbon-14 is radioactive and decays at a specific rate. It stops accumulating after the death of living things. This can be used to determine how old organic materials are.Burger explained that AMS can be used to date bones in skeletons with very little organic material.These results prove that Machu Picchu was occupied between 1420 and 1530 years earlier than previously believed. Researchers wrote that this suggests that Pachacuti rose in power and conquered neighboring areas before then.Hiram Bingham, an American professor at Yale University, led expeditions to explore Machu Picchu's mountaintop Inca citadel. (Image credit: Burger et al / Antiquity)Inca chronologyThe historical records that were created after the Spanish conquest of Machu Picchu in 16 century by the Spanish rulers of this region provided previous estimates of Machu Picchu's age. However, new discoveries make it difficult to trust the historical records of colonial forces.Burger said that modern radiocarbon methods are a better foundation to understand Inca chronology, than contradictory historical records.Dennis Ogburn, an archaeologist and anthropologist at the University of North Carolina, Charlotte, was not involved in the research. He said that the discrepancy of several centuries in the rise of Pachacuti's power would have implications for understanding Inca history.Ogburn explained to Live Science that the Inca chronology "shows not only how quickly their empire expanded but also how long it took them to consolidate control over the territories they conquered."He stated, "As we can revise the chronology based radiocarbon dates, it is becoming clear that the Inca started expanding the Empire three to four decades before the [historical] chronology indicated."He said that prior to the advent of radiocarbon dating such as AMS, there was little chance of refining the chronology for the Inca Empire. This is because it was an archaic-only phenomenon. "Radiocarbon dates from previous research didn't have the same resolution as we now and allow us to fine-tune things."These findings were published in Antiquity on Tuesday, August 3, 2013.Original publication on Live Science
