Bronze Age origin for Seahenge.

A nature warden walking along an isolated stretch of the eastern English coast in August 1998 came upon a startling, slightly eerie sight. With the tide drawn back, the huge, inverted stump of an oak tree appeared, inserted like a giant peg in the marshy soil. A ring of 55 oak posts surrounded the stump, forming a rough circle about 21 feet across.

The sea had gradually washed away a peat layer that had protected the mysterious wooden circle, exposing it to the damaging effects of saltwater and air. Local officials quickly contacted English Heritage, a London-based organization specializing in archaeological and historical matters. At that point, scientists recorded the site's layout and brought the threatened timber to a laboratory for study and preservation.

A new analysis shows that the timber circle--dubbed Seahenge, in a nod to England's famous Stonehenge site--dates to more than 4,000 years ago. The tree that provided the central stump either died or was felled in the spring of 2050 B.C., and the oaks for the surrounding posts were chopped down the next spring, according to a report in the Dec. 2 NATURE.

Thus, construction of the timber circle occurred at the start of Europe's Bronze Age, when metal tools and weapons debuted. "These people were farmers who cleared much of Britain's forest land, and now we've dated one of their religious temples," says David Miles, chief archaeologist of English Heritage.

Initial tree-ring analyses failed to yield a precise date for the timber circle. A tree adds a ring for each year of its life, and that ring achieves greater thickness when the climate favors growth. Comparisons of thickness patterns of tree rings with ice-core and other data on a region's past climate changes often can produce an age estimate for a tree. Researchers could not find clear links between the oak stump's rings and Britain's past weather swings, but all was not lost.

Radiocarbon analyses of the central oak indicated that it had died between 2200 B.C. and 2000 B.C., says Alex Bayliss of English Heritage. Bayliss' team then used a mathematical model to identify particularly strong consistencies between the tree-ring and radiocarbon findings. This allowed them to pinpoint the death dates for the stump and surrounding posts to a period of a few months in 2050 B.C. and 2049 B.C., respectively.

The central oak may have blown over in a storm, since it bears no ax marks, Miles says. Microscopic examination of the stump indicates that people hauled it into position with ropes made of honeysuckle. Broad gashes on the bark-covered outer posts resemble damage done by Early Bronze Age axes.