1952: An analysis of the carbon-14 radioisotope in a piece of charred oak from an excavated pit at Stonehenge estimates that the mysterious structure on England’s Salisbury Plain is 3,800 years old, plus or minus 275 years.
The carbon-dating process that dated Stonehenge to about 1848 B.C. was conducted by the technique’s godfather, Willard Libby. The University of Chicago professor developed radiocarbon dating in the late 1940s and won the 1960 Nobel Prize in chemistry for it.
When plants or animals die, they no longer exchange their carbon with fresh atoms from their environment. Thus, as the radioactive carbon-14 in dead matter decays to the more plentiful isotope carbon-12, the proportion of C-14 to C-12 declines. Carbon-14 has a half-life of about 5,600 years, so measuring the proportion of C-14 that’s still present in dead organic matter, and comparing it to the known proportion of C-14 in living matter, will indicate the age of the sample.
To be sure, carbon dating has its skeptics. Libby assumed C-14 broke down at a constant rate. However, the Archeology Expert website notes, “experimental evidence indicates that C-14 decay is slowing down and that millennia ago it decayed much faster than is observed today.”
The site points out that live mollusk shells in Hawaii were dated as 2,000 years old and a “freshly killed seal” in Antarctica dated 1,300 years. Improved techniques now date the earliest stone structures at Stonehenge to about 2600 B.C.
Whatever its exact age, as Time magazine noted when reporting the 1952 dating, Stonehenge has been “credited, at one time or another, to the Phoenicians, Celts, Romans, Sumerians, Druids and early Christians.”
Sir Joseph Norman Lockyer, who co-discovered helium and founded the journal, Nature, wrote in 1901 that the Heel Stone section of Stonehenge “had been originally aligned with the summer solstice” and calculated that it was built in 1800 B.C.
Further investigations have suggested that Stonehenge was an astronomical observatory, a place of worship and healing or perhaps a cemetery. Whatever its exact history, origins or age, thousands each year flock to Stonehenge to welcome the sun on the summer solstice.
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