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... Scientists say they've cracked a secret of the 6-ton rock at the center of Stonehenge " a discovery that only deepens the site's mystery.

The ancient monument's "altar stone," a sandstone rock at its center, likely originated in present-day Scotland, according to a study published Wednesday in the journal Nature. That means it was hauled more than 450 miles to southern England " significantly farther than any other stone at Stonehenge with known origins.

The finding raises profound questions. The researchers suspect the altar stone was installed about 4,500 years ago, which means that Neolithic people were able to move the rock hundreds of miles " long before lightweight, spoked wheels were invented.

The revelation also suggests that cultural and social structures were more interwoven in the British Isles at the time than previously realized, and that Neolithic people were capable of executing complex projects with relatively simple tools.

The discovery was based on an analysis of the age of mineral grains within the sandstone rock. After profiling the grains' ages, the researchers were able to compare the altar stone's age "fingerprint" to a database of sandstone samples across Britain and in nearby locations like Brittany, France.

"With quite a high degree of statistical certainty, in fact, bigger than 95% confidence, we can associate the age spectra to a very specific area in northeast Scotland," said Chris Kirkland, a co-author of the study and a professor of Earth and planetary sciences at Curtin University in Australia. ...