The only meteorite impact crater to be discovered anywhere in Britain or Ireland lies beneath a large area of Scotland, a scientist has suggested.
Dr Mike Simms, of Ulster Museum in Belfast, says has located the centre of the crater to be Lairg in Sutherland.
Patches of impact deposit, rock fragments thrown out when the meteorite hit, have been found elsewhere before.
But Dr Simms said he had now worked out the impact site and scale of the crater.
His findings have been published in the Proceedings of the Geologists' Association.
Evidence of the giant, ancient meteorite impact - deposits of green molten rock fragments mixed in with red sandstone "sandwiched" between sandstones almost 1.2 billion years old - was identified near Ullapool, in Wester Ross, in 2008 by geologists from Oxford and Aberdeen.
Dr Simms, a curator of palaeontology, studied geophysical maps of Scotland to find the impact site and to give a scale to the crater - it is at least 24 miles (40km) in diameter.
The centre at Lairg, a small community known for holding Europe's largest one-day sale of hill sheep, is buried under rock layers laid down after the impact.
Dr Simms said the impact released energy the equivalent to 1,500 billion tonnes of TNT explosives.
His research will be a feature of Channel 4 programme Walking Through Time, which is to be shown on 24 September.