A scientist claims to have discovered exactly where the first meteorite to hit the British Isles landed.
Palaeontologist Dr Mike Simms believes he has found the 25 mile-wide impact crater under the small town of Lairg in northern Scotland.
For years scientists have been studying green rock fragments found sandwiched between 1.2 billion-year-old sandstone near Ullapool, 30 miles to the west of Lairg.
For decades this layer was thought to be a volcanic mudflow until, in 2008, geologists from Oxford and Aberdeen proved that it actually had been formed by a giant meteorite impact.
But the location of the impact itself remained a mystery.
"When I visited the area on holiday in 2011 I found clues that the source of this unique layer - the impact crater - actually lies to the east," Dr Simms said.
"That raised the possibility that the crater might still exist somewhere on the Scottish mainland."
Dr Simms said geophysics helped lead him eastward to Lairg, using the principle that the sediment that filled the crater, and the fractured rock beneath it, would have a weaker gravitational pull than denser rock around the crater.
He said geophysical maps of Scotland indicated a large gravity anomaly centred on the town.
The scientist, who is curator of Palaeontology at the Ulster Museum, Belfast, said its similarity to gravity anomalies associated with impact craters around the world suggested that a vast crater was buried several miles beneath Lairg.
Dr Simms estimates the size of the crater at 25 miles across, which would make it one of the 15 largest craters on the planet.
He said the meteorite would have been around two miles in diameter and 13 billion tonnes in weight and would have penetrated five miles into the earth when it struck at 40,000 mph.
The story behind the discovery will be told on Saturday in Walking Through Time at 8pm on Channel 4.