The grains of sand that solve Stonehenge mystery after 5,000 years: Scientists uncover new evidence the stones were moved by humans – and not glaciers

The 5,000–year–old mystery of Stonehenge may have finally been solved – with the help of a few tiny grains of sand.

While most scientists believe that Stonehenge’s massive stones were dragged from Wales and Scotland, a rival theory proposes that the builders had a helping hand.

According to the so–called glacial transport theory, the ice that once covered ancient Britain conveniently carried the stones to the Salisbury Plain.

However, scientists have now found concrete evidence that suggests the megaliths must have been moved by humans.

Using cutting–edge mineral fingerprinting techniques, geologists from Curtin University showed that no glacial material ever reached the Salisbury Plain.

If the rocks were indeed carried by ice, they would have left behind a breadcrumb trail containing millions of microscopic mineral grains.

But when the researchers looked at Wiltshire’s sand, they found that none had been moved there during the last ice age, 20,000 to 26,000 years ago.

Lead author Dr Anthony Clarke told the Daily Mail: ‘Our findings make glacial transport unlikely and align with existing views that the megaliths were brought from distant sources by Neolithic people using methods like sledges, rollers, and rivers.’

One of Stonehenge’s most baffling features is the fact that its stones appear to originate from the most far–flung reaches of the UK.

While the large standing stones, or sarsens, come from an area just 15 miles (24 km) north of the stone circle, the smaller bluestones and the singular altar stone aren’t local.

Geologists have traced the two to five–tonne bluestones back to the Preseli Hills in Wales, while the six–tonne altar stone came from a location at least 460 miles (750 km) away in northern Scotland.

This means that Neolithic people would have needed to transport specifically selected stones over hundreds of miles using nothing more than stone and wooden tools.

For some researchers, this idea seems so unlikely that the glacial transport theory seems like a more reasonable alternative.

If ice did cover the Salisbury Plain sometime in the distant past, it would have left traces that should be visible today.

Many of these big traces, like scratches on the bedrock or carved landforms, are either missing or inconclusive around Stonehenge.

But the ice would have also left behind a microscopic trace that scientists should be able to see.

Dr Clarke says: ‘If large ice sheets had carried bluestone from Wales or northern Britain to Stonehenge, they would also have delivered huge volumes of sand and gravel debris with very distinctive age fingerprints into the local rivers and soils.’

Importantly, this sand contains two minerals called zircon and apatite that can be used like a ‘tiny geological clock’.

When zircon and apatite form, crystallising out of magma, they trap tiny amounts of radioactive uranium that decays into lead at a known rate.

By looking at the ratio of uranium to lead, scientists can work out how long ago an individual grain of sand was formed.

Since some rocks, like the Stonehenge megaliths, are made up of lots of these dateable grains, scientists can use this technique to create a geological ‘fingerprint’.

‘Because Britain’s bedrock has very different ages from place to place, a mineral’s age can indicate its source,’ says Dr Clarke.

‘This means that if glaciers had carried stones to Stonehenge, the rivers of Salisbury Plain, which gather zircon and apatite from across a wide area, should still contain a clear mineral fingerprint of that glacial journey.’

The researchers looked at more than 700 zircon and apatite grains, gathered from the rivers near Stonehenge.

Despite covering half the age of the Earth from around 2.8 billion years ago to 300 million years ago, almost none matched the fingerprint of the bluestones’ source in Wales or the altar stone’s source in Scotland.

The majority of the zircon grains came in a tight band from 1.7 to 1.1 billion years ago, when a blanket of loosely compacted sand called the Thanet Formation covered much of southern England.

Meanwhile, all of the apatite grains were dated to around 60 million years ago, which doesn’t match any potential rock source in Britain.

This is because the same tectonic forces that built the European Alps squeezed fluids through the chalk and ‘reset’ the apatite’s uranium clock.

Co–author Professor Chris Kirkland told the Daily Mail: ‘Salisbury Plain’s sediment story looks like recycling and reworking over long timescales, plus a Paleogene “shake–up” recorded in apatite, rather than a landscape built from major glacial imports.’

If ice had carried the bluestones or altar stone to England, the sand should have a clear signal from those points of origin.

‘However, the material around Stonehenge doesn’t,’ says Professor Kirkland.

‘So, we conclude Salisbury Plain remained unglaciated during the Pleistocene, making direct glacial transport of the megaliths unlikely.’

This gives ‘strong, testable evidence’ that the enormous stones were, in fact, dragged all the way to the Salisbury Plain by hand.

And that might mean we have to give a bit more credit to the ingenuity and determination of our ancient ancestors.

Professor Kirkland says: ‘You could propose a coastal movement by boat for the long legs, then final overland hauling using sledges, rollers, prepared trackways, and coordinated labour, especially for the largest stones.

‘If you think about this, it supports the idea of an advanced connected society in the Neolithic.’