Academic Reading — Test 76

Reading passage

In the spring of 1998, shifting sands along the beach at Holme-next-the-Sea on the north Norfolk coast exposed an extraordinary prehistoric monument. Where peat and tidal mud had long kept it hidden, a ring of split oak posts emerged, encircling a single massive tree stump that had been set into the ground upside down, its spreading roots reaching towards the sky. The site, soon nicknamed Seahenge by the press, consisted of fifty-five closely spaced timbers forming an oval enclosure roughly seven metres across. Although the popular name suggested a link with the famous stone circle at Stonehenge, the Norfolk structure was made entirely of wood and served a quite different, though still uncertain, purpose. Many archaeologists believe it was associated with funerary or ceremonial rites, perhaps a place where the dead were exposed rather than buried. The survival of the timbers was itself remarkable. Wood normally decays within a few years of being cut, but the waterlogged, oxygen-poor peat at Holme had sealed the oak away from the bacteria and fungi that would otherwise have destroyed it. This anaerobic environment preserved not only the shape of the posts but also the fine detail of their surfaces, including the marks left by the tools that had shaped them. Such conditions are uncommon, and they gave researchers an opportunity that is rarely available for monuments of this antiquity: the chance to study the original worked wood rather than mere impressions or stains in the soil. To establish when Seahenge had been built, archaeologists turned to dendrochronology, the science of dating wood by counting and measuring its annual growth rings. Each year a living tree adds a new layer of wood beneath its bark, and the width of that layer depends largely on the weather of the growing season. A warm, wet year tends to produce a broad ring, while a cold or dry one produces a narrow one. Because all the oaks growing in a particular region experience the same sequence of good and poor years, they develop a shared and distinctive pattern of wide and narrow rings. By matching the ring pattern of an unknown timber against a master chronology built from samples whose dates are already known, a specialist can often pin down the exact calendar year in which a tree was felled. The accuracy of the method depends on certain conditions being met. A reliable date requires a sample with a sufficient number of rings, since a short sequence may match the master pattern by chance rather than by genuine correspondence. It is also essential that the outermost rings, those formed just before the tree died, are present; without them the felling year cannot be determined precisely. The Seahenge timbers were well suited to this analysis because the oaks used had been mature trees with many rings, and the waterlogged conditions had preserved the all-important sapwood at the edge of several posts. The bark itself, the final layer beneath which the very last ring forms, had survived on some pieces. When the ring patterns were measured and compared with established oak chronologies for England, the results were unusually precise. The analysis showed that the trees forming the outer circle had been felled in the spring or early summer of 2049 BC, placing the construction of the monument firmly in the early Bronze Age. The central inverted stump was found to have been cut in the same period, which strongly suggested that the whole structure had been raised as a single planned project rather than added to over many years. Studies of the tool marks supported this conclusion, indicating that the builders had used bronze axes, several of which left distinct signatures on the wood. By comparing these marks, researchers estimated that at least fifty different axes had been employed, hinting that a sizeable community had taken part in the work. The dating of Seahenge demonstrates how much can be recovered when wood is preserved and the right techniques are applied. A monument that might once have been described only in vague terms as belonging to "prehistory" could now be tied to a single season more than four thousand years ago. After excavation, the timbers were removed from the beach for conservation, a decision that provoked some local opposition from those who felt the circle should have been left where it lay. They were taken to be treated and eventually displayed in a museum, where the public could see the worked surfaces that the peat had protected for so long. The episode remains a striking illustration of the partnership between careful fieldwork and the patient reading of tree rings.