Photo credit: phys.org
During the solstice events, people flock to Stonehenge on Salisbury Plain in England, where they mark the astronomical significance of this iconic monument. Central to their celebrations is the Altar Stone, a substantial sandstone slab weighing six tons that lies at the heart of Stonehenge.
This ancient structure was erected between 3,100 and 1,600 BCE by a society that left no written documentation. However, the megaliths that comprise Stonehenge can provide insights into its origins. The stone types are primarily categorized into two: sarsen stones and bluestones, with the Altar Stone being the most prominent bluestone.
It is believed that some bluestones originated from the Mynydd Preseli in Wales, located over 220 kilometers away, whereas the sarsen stones were sourced locally from the Salisbury Plain. However, the origin of the Altar Stone has remained a point of contention, as recent research has called into question the assumption that it, too, was Welsh in origin.
Through an analysis of the mineral grains that comprise the Altar Stone, researchers have published their findings in Nature, suggesting that this monument’s centerpiece actually comes from Scotland.
The Mineral DNA of Rocks
At dawn during the summer solstice, sunlight illuminates the Altar Stone, and during the winter solstice, the setting sun bathes it in a soft glow. This striking scene likely mirrors what ancient inhabitants experienced, using the stone to celebrate the return of longer days of light.
Despite the monument’s celestial significance, many questions remain regarding its construction and purpose. Just as human DNA can reveal information about lineage and experiences, the mineral makeup of the Altar Stone contains details about its geological history and formation.
In their study, scientists dated specific mineral grains, namely zircon, rutile, and apatite. As contemporary geologists cannot extract samples from the Altar Stone, they utilized thin sections collected from earlier archaeological excavations.
This mineral analysis allowed researchers to trace the source of the grains back to their origin, much like genealogical tests identify ancestral homelands. The findings pointed to sedimentary deposits in the Orcadian Basin of northeastern Scotland as the closest match for the stone’s constituents.
Detrital particles from the Grampian Mountains and Northern Highlands have washed into the Orcadian Basin for approximately 400 million years, embedding unique characteristics that trace back to their origin in sandstone chosen for the Altar Stone.
The Scottish Roots of Stonehenge
While today northeastern Scotland and the Orkney Islands have low population densities, archaeological evidence such as Skara Brae, Maeshowe, and the Ring of Brodgar indicate a vibrant Neolithic community filled with culture and trade.
The idea that the Altar Stone hails from Scotland raises intriguing questions about the connectivity and technological expertise of prehistoric societies in Britain. A network for trading quarried stone tools spanned Britain, Ireland, and parts of continental Europe, exemplified by the discovery of a saddle quern from Normandy in Dorset.
The Journey of the Altar Stone
While some theories suggest that glaciers may have moved the Welsh bluestones to Stonehenge, this does not appear plausible for the Altar Stone’s journey from Scotland.
During the Ice Ages, massive glaciers traveled south from the Scottish Highlands toward the Orcadian Basin, pushing rocks further from their destination at Salisbury Plain. The geography of Neolithic Britain, characterized by dense forests and challenging terrains, would have complicating overland transport.
It is more likely that the builders of Stonehenge utilized maritime routes to transport the Altar Stone, a method supported by historical evidence of similar practices. The remnants of the Hanson Log Boat demonstrate that shaped stone blocks were moved via waterways as early as 1500 BC.
However, the central question lingers: why was the Altar Stone chosen for relocation? What compelled the transport of this unassuming greenish-gray sandstone slab over a distance exceeding 650 kilometers?
Humankind’s affinity for selecting the ideal building stone is not new. This preference continues even today, as evidenced by socialite Kim Kardashian’s extravagant purchase of marble from Italy for her home. To us, such choices may seem extravagant, especially when local alternatives are available.
Perhaps ancient Britons viewed the Altar Stone with a similar lens, or perhaps more functional reasons influenced the decision, such as its ability to be easily quarried and shipped via accessible marine routes.
Source
phys.org