The Stonehenge altar stone will come from Scotland, 750 kilometres away from the site.

In popular science, the word “mystery” is sometimes overused, but it is still appropriate to use it in the context of Stonehenge. The reasons why Neolithic humans built this famous megalithic site in southern England five thousand years ago are still elusive. One of the mysteries concerns square 80, the so-called “altar” stone, which occupies the centre of the megalith circle. We have only a vague idea of ​​when it arrived at Stonehenge, probably around the middle of the Third^H Millennium BC. We also do not know whether this block, now broken and half-buried under two other large stones that fell on it, ever stood. Nor do we know its symbolism and function.

We also raised many questions about where it came from, the hypothesis of a Welsh origin – which has been proven for many other bluestones – which was recently ruled out by Richard Bivins and Nick Pearce, two researchers from Aberystwyth University (Wales), who have been working at Stonehenge for about fifteen years. Supported by colleagues from Curtin University (Perth, Australia), this duo surprised everyone – and themselves at the same time – certainly, In a study published by nature Wednesday, August 14The altar stone came from the far north-east of Scotland, 750 kilometers from Stonehenge! As Nick Pearce explained on August 13 during a press conference call, this result “It was completely unexpected. [Il] I never imagined[t] Not such a distant origin ».

Green Shades Sandstone

Before we ask how and why prehistoric humans went to such lengths to find a 6-ton block, it is necessary to explain how researchers came to this amazing discovery. This parallelepiped is 5 meters long, 1 meter wide and 50 centimeters thick, and is made of greenish-hued sandstone. Geology teaches that sandstone is what is called a clastic rock, meaning that the grains that form it come from the disintegration of other, older rocks. From different origins and ages, they were reconstituted to form sandstone.

Study authors nature They worked with several grains (zircon, apatite and rutile) from the altar stone, and determined their age using radiometric dating techniques. These work on the same principle as carbon-14 dating, which is used for organic materials. But while carbon-14 dating can only take you back fifty thousand years, the radioactive isotopes studied by geologists, such as uranium or lutetium, make it possible to trace minerals back billions of years. Thus the zircon grains from Stone 80 are dated to between one and two billion years ago.

You have 45.6% of this article left to read. The rest is reserved for subscribers.