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Philip Lingard reports for BBC News
"The date is extraordinarily precise"
 real 28k

Alex Bayliss, English Heritage
"We used a new approach combining two techniques"
 real 28k

Wednesday, 1 December, 1999, 19:04 GMT
Seahenge dated to spring 2050 BC
Seahenge will be returned to the Norfolk area

Seahenge, the remarkable ring of oak timbers recently uncovered on a UK beach, is exactly 4,050 years old.

Scientists working with English Heritage have come up with the age by combining a number of techniques, including complex mathematics.

The researchers are so confident in their findings they are even prepared to say that the central stump of the wooden ring came from a tree which was felled or died between April and June 2050 BC. They believe the other trees used for the surrounding posts were cut down in the spring of the following year, 2049 BC.

The dating confirms the authenticity of Seahenge, which was almost certainly used as a ceremonial site in its day. Some will also regard it as further justification for the decision to remove the circle from the sands where they were found at Holme-next-the-Sea, Norfolk.

Although druid groups opposed the operation, subsequent examination of the posts has shown that the exposed wood was deteriorating much faster than anyone had suspected. If Seahenge had been left where it was built, the world would soon have lost what many now regard as the Bronze Age discovery of the decade.

Climate and growth rings

To date the central upturned stump, scientists at English Heritage resorted first to dendochronology, which matches the growth rings in wood to known historical climate data. This would normally have given a very accurate date for the tree's birth and death but this proved problematic in this case because the oak's ring patterns loosely fitted too many parts of Britain's past weather spectrum.

 From the BBC Archive: Seahenge is removed

The team also used radiocarbon analysis, which studies the decay of natural carbon isotopes to date organic material. For accuracy, six different samples were taken. These results showed that the tree died between 2200 BC and 2000 BC.

The timbers have been taken to Flag Fen to be studied The timbers have been taken to Flag Fen to be studied
"But we wanted an exact date," said Alex Bayliss, Scientific Dating Co-ordinator at English Heritage. It was then that she turned to the complex mathematics devised by an 18th Century vicar, Thomas Bayes.

The Bayesian mathematical model can calculate and recombine probabilities contained in different data sets to produce a very narrow range of outcomes. This work showed that the tree had died sometime between April and June 2050 BC."

The same type of analysis was applied to the data for the surrounding posts.

Human timescales

Alex Bayliss told BBC News Online: "This is the really important thing about this research: by using Bayesian mathematics we are bringing down pre-historic timescales, ranges that cover decades or hundreds of years, to within that of human experience - a lifetime."

 From the BBC Archive: Archaeologist Maisie Taylor describes the preservation work at Flag Fen

The dating fits with work done at the Flag Fen Bronze Age site and research centre at Peterborough where the timbers were taken after being removed from the beach. Archaeologists at Flag Fen say the type of axe marks left in the wood indicate a level of technology known to have existed around that time.

How Seahenge could have looked How Seahenge could have looked
"It is very unusual to pin a precise date to a major ceremonial site, but we've done that," said David Miles, Chief Archaeologist for English Heritage.

"We know that the circle was created at the very start of the Bronze Age, when metal tools and weapons replaced stone implements for the first time. These people were farmers who cleared much of Britain's forest land and now we have dated one of their religious temples. It is tremendously exciting."

The timbers of Seahenge will be returned to Norfolk when a future for the wooden circle has been decided.

Details of the dating are published in the scientific journal Nature.

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See also:
08 Jul 99 |  Sci/Tech
Seahenge gives up its secrets
26 May 99 |  Sci/Tech
'Seahenge' moves on
09 Nov 99 |  Sci/Tech
Facing up to the Stone Age

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