Scientists working in Scotland have uncovered evidence of the biggest meteorite ever to hit the British Isles.
They believe the meteorite struck about 1.2 billion years ago near Ullapool.
They found what they believe to be ejected material from a meteorite crater beneath a layer of rock.
They said the material had scattered over a distance of about 30 miles.
It had previously been thought that the unusual rock formations in the area had been formed by volcanic activity.
But the volcanic origins of the rock have always been questioned because there are no volcanic vents or other volcanic sediments nearby.
The findings were made by scientists from Oxford and Aberdeen universities, and feature in the journal Geology.
Ken Amor of Oxford University's department of earth sciences, and co-author of the Geology paper, said chemical tests had shown signs of meteoritic material.
He said: "This is the most spectacular evidence for a meteorite impact within the British Isles found to date, and what we have discovered about this meteorite strike could help us to understand the ancient impacts that shaped the surface of other planets, such as Mars."
He added: "If there had been human observers in Scotland 1.2 billion years ago they would have seen quite a show."
Since the formation of the solar system, leftover space material has collided regularly with Earth, where there are about 174 known craters or their remnants.
Scott Thackrey, co-author of the report, said the meteorite would have measured more than half a mile (900 metres to one kilometre) in diameter.
A seven-mile-wide (12km) crater was created when it hit the Highlands, he believes.
The crater is thought to be the biggest in the UK but is dwarfed by the largest known example, the 186-mile wide (300km) Vredefort crater in South Africa, Mr Thackrey said.
The PhD student at Aberdeen University's geology department said: "The size of craters varies a lot.
"On Earth they get eroded away quite quickly so we were pleased to find this example."
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